The two title 5-oxa-2,6-diazaspiro[3.4]octan-1-one adducts, 7-benzoyl-2-(4-methoxyphenyl)-6-phenyl-5-oxa-2,6-diazaspiro[3.4]octan-1-one, C25H22N2O4, (III), and 6-tert-butyl-2-(4-methylphenyl)-7-phenyl-5-oxa-2,6-diazaspiro[3.4]octan-1-one, C22H26N2O2, (IV), were obtained from a stereospecific [3+2] 1,3-cycloaddition of 3-methylene azetidin-2-ones as dipolarophiles with nitrones. The lactam ring is conjugated with the p-methoxyphenyl or p-methylphenyl moiety. The envelope conformations of the isoxazolidine rings in (III) and (IV) are different, leading the substituents to be pseudo-axial in (III) and pseudo-equatorial in (IV).
Supporting information
CCDC references: 144643; 144644
Compounds (III) and (IV) were obtained from dipolar cycloadditions of (I) and
(II) in toluene at 353 K. Crystals were isolated by recrystallization from
ethanol solutions.
The coordinates of the methyl H atoms on C17 in (III) were refined isotropically
(C—H distances ?.??-?.??Å). All other H atoms were treated as riding.
For both compounds, data collection: CAD-4 Software (Enraf-Nonius, 1987); cell refinement: CAD-4 Software; data reduction: NONIUS (Riche, 1989); program(s) used to solve structure: SHELXS86 (Sheldrick, 1990); program(s) used to refine structure: SHELXL93 (Sheldrick, 1993); molecular graphics: R3M (Riche, 1983) and ORTEP (Johnson, 1965).
(III) 7-benzoyl-2-(4-methoxyphenyl)-6-phenyl-5-oxa-2,6-diazaspiro[3.4]octan-1-one
top
Crystal data top
C25H22N2O4 | Dx = 1.322 Mg m−3 |
Mr = 414.45 | Melting point = 428–429 K |
Monoclinic, P21/n | Cu Kα radiation, λ = 1.54180 Å |
a = 9.368 (5) Å | Cell parameters from 25 reflections |
b = 19.776 (7) Å | θ = 9.6–18.2° |
c = 11.484 (8) Å | µ = 0.74 mm−1 |
β = 101.92 (4)° | T = 293 K |
V = 2082 (2) Å3 | Prism, colourless |
Z = 4 | 0.36 × 0.20 × 0.13 mm |
F(000) = 872 | |
Data collection top
Enraf-Nonius CAD4 diffractometer | Rint = 0.043 |
Radiation source: fine-focus sealed tube | θmax = 67.0°, θmin = 4.5° |
Graphite monochromator | h = −11→10 |
θ/2θ scans | k = −20→23 |
6167 measured reflections | l = 0→13 |
3711 independent reflections | 3 standard reflections every 120 min |
2276 reflections with I > 2σ(I) | intensity decay: 2% |
Refinement top
Refinement on F2 | Secondary atom site location: difference Fourier map |
Least-squares matrix: full | Hydrogen site location: inferred from neighbouring sites |
R[F2 > 2σ(F2)] = 0.050 | H atoms treated by a mixture of independent and constrained refinement |
wR(F2) = 0.120 | Calculated w = 1/[σ2(Fo2) + (0.0724P)2 + 0.164P] where P = (Fo2 + 2Fc2)/3 |
S = 1.01 | (Δ/σ)max = −0.013 |
3711 reflections | Δρmax = 0.21 e Å−3 |
282 parameters | Δρmin = −0.19 e Å−3 |
0 restraints | Extinction correction: SHELXL93 (Sheldrick, 1993), Fc*=kFc[1+0.001xFc2λ3/sin(2θ)]-1/4 |
Primary atom site location: structure-invariant direct methods | Extinction coefficient: 0.0026 (4) |
Crystal data top
C25H22N2O4 | V = 2082 (2) Å3 |
Mr = 414.45 | Z = 4 |
Monoclinic, P21/n | Cu Kα radiation |
a = 9.368 (5) Å | µ = 0.74 mm−1 |
b = 19.776 (7) Å | T = 293 K |
c = 11.484 (8) Å | 0.36 × 0.20 × 0.13 mm |
β = 101.92 (4)° | |
Data collection top
Enraf-Nonius CAD4 diffractometer | Rint = 0.043 |
6167 measured reflections | 3 standard reflections every 120 min |
3711 independent reflections | intensity decay: 2% |
2276 reflections with I > 2σ(I) | |
Refinement top
R[F2 > 2σ(F2)] = 0.050 | 0 restraints |
wR(F2) = 0.120 | H atoms treated by a mixture of independent and constrained refinement |
S = 1.01 | Δρmax = 0.21 e Å−3 |
3711 reflections | Δρmin = −0.19 e Å−3 |
282 parameters | |
Special details top
Geometry. All e.s.d.'s (except the e.s.d. in the dihedral angle between two l.s. planes)
are estimated using the full covariance matrix. The cell e.s.d.'s are taken
into account individually in the estimation of e.s.d.'s in distances, angles
and torsion angles; correlations between e.s.d.'s in cell parameters are only
used when they are defined by crystal symmetry. An approximate (isotropic)
treatment of cell e.s.d.'s is used for estimating e.s.d.'s involving l.s.
planes. |
Refinement. Refinement on F2 for ALL reflections except for 0 with very negative
F2 or flagged by the user for potential systematic errors. Weighted
R-factors wR and all goodnesses of fit S are based on
F2, conventional R-factors R are based on F,
with F set to zero for negative F2. The observed criterion of
F2 > σ(F2) is used only for calculating _R_factor_obs
etc. and is not relevant to the choice of reflections for refinement.
R-factors based on F2 are statistically about twice as large
as those based on F, and R- factors based on ALL data will be
even larger. |
Fractional atomic coordinates and isotropic or equivalent isotropic displacement parameters (Å2) top | x | y | z | Uiso*/Ueq | |
C1 | −0.2160 (2) | 0.09152 (11) | 0.5334 (2) | 0.0530 (6) | |
N2 | −0.2516 (2) | 0.12935 (9) | 0.6222 (2) | 0.0546 (5) | |
C3 | −0.1230 (3) | 0.17395 (12) | 0.6373 (2) | 0.0606 (7) | |
H3A | −0.0600 | 0.17178 | 0.7157 | 0.073* | |
H3B | −0.1456 | 0.22039 | 0.6131 | 0.073* | |
C4 | −0.0710 (2) | 0.13078 (11) | 0.5434 (2) | 0.0532 (6) | |
O5 | −0.0531 (2) | 0.16853 (7) | 0.44033 (15) | 0.0577 (5) | |
N6 | 0.0715 (2) | 0.14217 (9) | 0.3979 (2) | 0.0521 (5) | |
C7 | 0.1703 (2) | 0.12119 (11) | 0.5092 (2) | 0.0516 (6) | |
H7 | 0.2416 | 0.08794 | 0.4935 | 0.062* | |
C8 | 0.0696 (2) | 0.09035 (12) | 0.5829 (2) | 0.0547 (6) | |
H8A | 0.1087 | 0.09596 | 0.6674 | 0.066* | |
H8B | 0.0537 | 0.04262 | 0.5655 | 0.066* | |
O9 | −0.2763 (2) | 0.04440 (8) | 0.4760 (2) | 0.0636 (5) | |
C10 | −0.3512 (2) | 0.12200 (11) | 0.6979 (2) | 0.0525 (6) | |
C11 | −0.3413 (3) | 0.16374 (14) | 0.7952 (3) | 0.0692 (7) | |
H11 | −0.2733 | 0.19865 | 0.8066 | 0.083* | |
C12 | −0.4291 (3) | 0.15501 (15) | 0.8753 (3) | 0.0791 (9) | |
H12 | −0.4204 | 0.18352 | 0.9408 | 0.095* | |
C13 | −0.5314 (3) | 0.10334 (15) | 0.8583 (3) | 0.0713 (8) | |
C14 | −0.5453 (3) | 0.06272 (13) | 0.7586 (2) | 0.0652 (7) | |
H14 | −0.6156 | 0.02881 | 0.7459 | 0.078* | |
C15 | −0.4574 (2) | 0.07158 (11) | 0.6782 (2) | 0.0558 (6) | |
H15 | −0.4684 | 0.04420 | 0.6110 | 0.067* | |
O16 | −0.6222 (2) | 0.08993 (13) | 0.9351 (2) | 0.1058 (8) | |
C17 | −0.5825 (4) | 0.1119 (2) | 1.0514 (3) | 0.1034 (11) | |
H17A | −0.6455 (17) | 0.0918 (10) | 1.0978 (6) | 0.145* | |
H17B | −0.591 (3) | 0.1602 (2) | 1.0538 (4) | 0.145* | |
H17C | −0.4834 (9) | 0.0989 (11) | 1.0835 (8) | 0.145* | |
C18 | 0.2463 (3) | 0.18565 (12) | 0.5645 (2) | 0.0561 (6) | |
O19 | 0.2044 (2) | 0.21298 (10) | 0.6458 (2) | 0.0880 (7) | |
C20 | 0.3685 (2) | 0.21479 (11) | 0.5151 (2) | 0.0535 (6) | |
C21 | 0.4331 (3) | 0.27318 (13) | 0.5663 (3) | 0.0743 (8) | |
H21 | 0.4003 | 0.29293 | 0.6294 | 0.089* | |
C22 | 0.5462 (3) | 0.3025 (2) | 0.5243 (3) | 0.0904 (10) | |
H22 | 0.5890 | 0.3419 | 0.5595 | 0.109* | |
C23 | 0.5956 (3) | 0.2745 (2) | 0.4326 (3) | 0.0834 (9) | |
H23 | 0.6712 | 0.2950 | 0.4044 | 0.100* | |
C24 | 0.5342 (3) | 0.21589 (15) | 0.3813 (3) | 0.0751 (8) | |
H24 | 0.5691 | 0.19606 | 0.3192 | 0.090* | |
C25 | 0.4193 (3) | 0.18628 (13) | 0.4225 (2) | 0.0647 (7) | |
H25 | 0.3766 | 0.14690 | 0.3871 | 0.078* | |
C26 | 0.0272 (3) | 0.09079 (11) | 0.3107 (2) | 0.0507 (6) | |
C27 | 0.1302 (3) | 0.04808 (12) | 0.2785 (2) | 0.0600 (6) | |
H27 | 0.2273 | 0.05118 | 0.3177 | 0.072* | |
C28 | 0.0899 (3) | 0.00099 (13) | 0.1887 (2) | 0.0669 (7) | |
H28 | 0.1599 | −0.02722 | 0.1677 | 0.080* | |
C29 | −0.0537 (3) | −0.00425 (14) | 0.1303 (2) | 0.0708 (8) | |
H29 | −0.0817 | −0.03684 | 0.0716 | 0.085* | |
C30 | −0.1546 (3) | 0.03891 (15) | 0.1594 (2) | 0.0698 (7) | |
H30 | −0.2510 | 0.03637 | 0.1182 | 0.084* | |
C31 | −0.1166 (3) | 0.08612 (13) | 0.2486 (2) | 0.0614 (7) | |
H31 | −0.1871 | 0.11490 | 0.2673 | 0.074* | |
Atomic displacement parameters (Å2) top | U11 | U22 | U33 | U12 | U13 | U23 |
C1 | 0.0511 (13) | 0.0473 (13) | 0.0591 (15) | −0.0004 (11) | 0.0083 (11) | 0.0014 (12) |
N2 | 0.0507 (11) | 0.0510 (11) | 0.0631 (12) | −0.0072 (9) | 0.0141 (10) | −0.0060 (10) |
C3 | 0.0577 (14) | 0.0543 (14) | 0.072 (2) | −0.0111 (12) | 0.0180 (13) | −0.0068 (12) |
C4 | 0.0532 (13) | 0.0487 (13) | 0.0585 (14) | −0.0052 (11) | 0.0136 (11) | 0.0021 (12) |
O5 | 0.0586 (10) | 0.0487 (9) | 0.0687 (11) | 0.0077 (7) | 0.0196 (8) | 0.0099 (8) |
N6 | 0.0511 (11) | 0.0475 (11) | 0.0595 (12) | 0.0023 (8) | 0.0154 (9) | 0.0051 (9) |
C7 | 0.0504 (12) | 0.0433 (12) | 0.0609 (14) | −0.0001 (10) | 0.0111 (11) | 0.0026 (11) |
C8 | 0.0517 (13) | 0.0501 (13) | 0.063 (2) | −0.0016 (10) | 0.0130 (12) | 0.0048 (11) |
O9 | 0.0638 (10) | 0.0549 (10) | 0.0719 (11) | −0.0096 (8) | 0.0138 (9) | −0.0126 (9) |
C10 | 0.0438 (12) | 0.0507 (13) | 0.063 (2) | −0.0003 (10) | 0.0101 (11) | −0.0039 (12) |
C11 | 0.061 (2) | 0.069 (2) | 0.082 (2) | −0.0172 (13) | 0.0240 (14) | −0.0241 (15) |
C12 | 0.077 (2) | 0.081 (2) | 0.087 (2) | −0.0182 (15) | 0.035 (2) | −0.032 (2) |
C13 | 0.059 (2) | 0.080 (2) | 0.080 (2) | −0.0068 (14) | 0.0268 (15) | −0.013 (2) |
C14 | 0.0490 (14) | 0.066 (2) | 0.082 (2) | −0.0098 (12) | 0.0165 (13) | −0.0068 (14) |
C15 | 0.0482 (13) | 0.0540 (13) | 0.064 (2) | −0.0021 (11) | 0.0093 (12) | −0.0073 (12) |
O16 | 0.093 (2) | 0.135 (2) | 0.105 (2) | −0.0396 (14) | 0.0555 (14) | −0.037 (2) |
C17 | 0.082 (2) | 0.143 (3) | 0.094 (3) | 0.018 (2) | 0.038 (2) | 0.006 (2) |
C18 | 0.0552 (14) | 0.0514 (13) | 0.064 (2) | −0.0035 (11) | 0.0169 (12) | −0.0047 (12) |
O19 | 0.0893 (14) | 0.0847 (14) | 0.101 (2) | −0.0267 (11) | 0.0450 (13) | −0.0371 (12) |
C20 | 0.0490 (13) | 0.0449 (13) | 0.064 (2) | −0.0012 (10) | 0.0061 (11) | 0.0028 (11) |
C21 | 0.068 (2) | 0.058 (2) | 0.097 (2) | −0.0155 (13) | 0.017 (2) | −0.009 (2) |
C22 | 0.082 (2) | 0.077 (2) | 0.111 (3) | −0.031 (2) | 0.018 (2) | −0.009 (2) |
C23 | 0.059 (2) | 0.089 (2) | 0.098 (2) | −0.020 (2) | 0.006 (2) | 0.023 (2) |
C24 | 0.066 (2) | 0.083 (2) | 0.080 (2) | 0.000 (2) | 0.0228 (15) | 0.011 (2) |
C25 | 0.063 (2) | 0.0585 (15) | 0.074 (2) | −0.0074 (12) | 0.0190 (14) | 0.0013 (13) |
C26 | 0.0585 (14) | 0.0461 (12) | 0.0491 (13) | −0.0045 (10) | 0.0149 (11) | 0.0095 (11) |
C27 | 0.065 (2) | 0.0574 (14) | 0.058 (2) | 0.0031 (12) | 0.0123 (13) | 0.0036 (13) |
C28 | 0.080 (2) | 0.066 (2) | 0.057 (2) | 0.0066 (14) | 0.0200 (14) | 0.0022 (14) |
C29 | 0.088 (2) | 0.073 (2) | 0.054 (2) | −0.015 (2) | 0.0191 (15) | 0.0004 (14) |
C30 | 0.064 (2) | 0.087 (2) | 0.058 (2) | −0.0194 (15) | 0.0113 (14) | 0.003 (2) |
C31 | 0.0570 (15) | 0.068 (2) | 0.060 (2) | −0.0025 (12) | 0.0146 (12) | 0.0085 (13) |
Geometric parameters (Å, º) top
C1—O9 | 1.212 (3) | C13—C14 | 1.382 (4) |
C1—N2 | 1.361 (3) | C14—C15 | 1.370 (4) |
C1—C4 | 1.548 (3) | O16—C17 | 1.380 (4) |
N2—C10 | 1.408 (3) | C18—O19 | 1.212 (3) |
N2—C3 | 1.475 (3) | C18—C20 | 1.494 (3) |
C3—C4 | 1.532 (3) | C20—C25 | 1.373 (4) |
C4—O5 | 1.438 (3) | C20—C21 | 1.378 (3) |
O5—N6 | 1.452 (2) | C21—C22 | 1.378 (4) |
N6—C7 | 1.474 (3) | C22—C23 | 1.354 (5) |
C7—C8 | 1.520 (3) | C23—C24 | 1.372 (4) |
C4—C8 | 1.527 (3) | C24—C25 | 1.391 (4) |
N6—C26 | 1.427 (3) | C26—C27 | 1.389 (3) |
C7—C18 | 1.532 (3) | C26—C31 | 1.391 (3) |
C10—C11 | 1.377 (3) | C27—C28 | 1.383 (4) |
C10—C15 | 1.394 (3) | C28—C29 | 1.378 (4) |
C11—C12 | 1.366 (4) | C29—C30 | 1.365 (4) |
C12—C13 | 1.387 (4) | C30—C31 | 1.377 (4) |
C13—O16 | 1.372 (3) | | |
| | | |
O9—C1—N2 | 132.2 (2) | O16—C13—C14 | 117.1 (2) |
O9—C1—C4 | 136.9 (2) | O16—C13—C12 | 123.6 (3) |
N2—C1—C4 | 90.9 (2) | C14—C13—C12 | 119.3 (3) |
C1—N2—C10 | 134.6 (2) | C15—C14—C13 | 121.1 (2) |
C1—N2—C3 | 95.5 (2) | C14—C15—C10 | 119.4 (2) |
C10—N2—C3 | 128.2 (2) | C13—O16—C17 | 118.8 (2) |
N2—C3—C4 | 87.4 (2) | O19—C18—C20 | 121.0 (2) |
O5—C4—C8 | 106.1 (2) | O19—C18—C7 | 119.6 (2) |
O5—C4—C3 | 113.5 (2) | C20—C18—C7 | 119.4 (2) |
C8—C4—C3 | 117.5 (2) | C25—C20—C21 | 118.9 (2) |
O5—C4—C1 | 116.7 (2) | C25—C20—C18 | 123.4 (2) |
C8—C4—C1 | 116.7 (2) | C21—C20—C18 | 117.7 (2) |
C1—C4—C3 | 86.0 (2) | C20—C21—C22 | 120.3 (3) |
C4—O5—N6 | 109.2 (2) | C23—C22—C21 | 120.8 (3) |
O5—N6—C26 | 110.7 (2) | C22—C23—C24 | 119.9 (3) |
C26—N6—C7 | 116.6 (2) | C23—C24—C25 | 119.7 (3) |
O5—N6—C7 | 102.4 (2) | C20—C25—C24 | 120.5 (3) |
N6—C7—C8 | 104.2 (2) | C27—C26—C31 | 118.4 (2) |
N6—C7—C18 | 106.3 (2) | C27—C26—N6 | 120.2 (2) |
C8—C7—C18 | 113.0 (2) | C31—C26—N6 | 121.2 (2) |
C4—C8—C7 | 102.7 (2) | C28—C27—C26 | 120.7 (2) |
C11—C10—C15 | 119.2 (2) | C29—C28—C27 | 120.2 (3) |
C11—C10—N2 | 119.8 (2) | C30—C29—C28 | 119.3 (3) |
C15—C10—N2 | 121.0 (2) | C29—C30—C31 | 121.4 (3) |
C12—C11—C10 | 121.5 (2) | C30—C31—C26 | 120.0 (3) |
C11—C12—C13 | 119.5 (3) | | |
| | | |
O9—C1—N2—C10 | 15.1 (4) | C11—C12—C13—C14 | −1.8 (4) |
C4—C1—N2—C10 | −162.3 (2) | O16—C13—C14—C15 | −178.7 (2) |
O9—C1—N2—C3 | −179.3 (3) | C12—C13—C14—C15 | 1.7 (4) |
C4—C1—N2—C3 | 3.3 (2) | C13—C14—C15—C10 | 0.6 (4) |
C1—N2—C3—C4 | −3.4 (2) | C11—C10—C15—C14 | −2.8 (4) |
C10—N2—C3—C4 | 163.6 (2) | N2—C10—C15—C14 | 175.2 (2) |
N2—C3—C4—O5 | 120.4 (2) | C14—C13—O16—C17 | 158.4 (3) |
N2—C3—C4—C8 | −115.1 (2) | C12—C13—O16—C17 | −22.1 (5) |
N2—C3—C4—C1 | 3.0 (2) | N6—C7—C18—O19 | 101.0 (3) |
O9—C1—C4—O5 | 65.3 (4) | C8—C7—C18—O19 | −12.7 (3) |
N2—C1—C4—O5 | −117.5 (2) | N6—C7—C18—C20 | −77.4 (2) |
O9—C1—C4—C8 | −61.5 (4) | C8—C7—C18—C20 | 168.9 (2) |
N2—C1—C4—C8 | 115.7 (2) | O19—C18—C20—C25 | −179.4 (3) |
O9—C1—C4—C3 | 179.6 (3) | C7—C18—C20—C25 | −1.0 (3) |
N2—C1—C4—C3 | −3.2 (2) | O19—C18—C20—C21 | 0.9 (4) |
C8—C4—O5—N6 | 13.5 (2) | C7—C18—C20—C21 | 179.3 (2) |
C3—C4—O5—N6 | 144.0 (2) | C25—C20—C21—C22 | 0.4 (4) |
C1—C4—O5—N6 | −118.4 (2) | C18—C20—C21—C22 | −179.9 (3) |
C4—O5—N6—C26 | 91.6 (2) | C20—C21—C22—C23 | −0.1 (5) |
C4—O5—N6—C7 | −33.3 (2) | C21—C22—C23—C24 | −0.8 (5) |
O5—N6—C7—C8 | 39.5 (2) | C22—C23—C24—C25 | 1.2 (4) |
C26—N6—C7—C8 | −81.5 (2) | C21—C20—C25—C24 | 0.1 (4) |
C26—N6—C7—C18 | 158.9 (2) | C18—C20—C25—C24 | −179.6 (2) |
O5—N6—C7—C18 | −80.1 (2) | C23—C24—C25—C20 | −0.9 (4) |
N6—C7—C8—C4 | −31.3 (2) | O5—N6—C26—C27 | −165.0 (2) |
C18—C7—C8—C4 | 83.6 (2) | C7—N6—C26—C27 | −48.6 (3) |
O5—C4—C8—C7 | 11.2 (2) | O5—N6—C26—C31 | 20.8 (3) |
C3—C4—C8—C7 | −116.9 (2) | C7—N6—C26—C31 | 137.3 (2) |
C1—C4—C8—C7 | 143.1 (2) | C31—C26—C27—C28 | −1.5 (3) |
C1—N2—C10—C11 | 167.5 (3) | N6—C26—C27—C28 | −175.8 (2) |
C3—N2—C10—C11 | 5.8 (4) | C26—C27—C28—C29 | −0.3 (4) |
C1—N2—C10—C15 | −10.5 (4) | C27—C28—C29—C30 | 2.1 (4) |
C3—N2—C10—C15 | −172.2 (2) | C28—C29—C30—C31 | −2.1 (4) |
C15—C10—C11—C12 | 2.8 (4) | C29—C30—C31—C26 | 0.3 (4) |
N2—C10—C11—C12 | −175.3 (2) | C27—C26—C31—C30 | 1.5 (3) |
C10—C11—C12—C13 | −0.5 (5) | N6—C26—C31—C30 | 175.7 (2) |
C11—C12—C13—O16 | 178.7 (3) | | |
(IV) 6-
tert-butyl-2-(4-methylphenyl)-7-phenyl-5-oxa-2,6-diazaspiro[3.4]octan-1-one
top
Crystal data top
C22H26N2O2 | F(000) = 376 |
Mr = 350.45 | Dx = 1.170 Mg m−3 |
Triclinic, P1 | Melting point = 413–414 K |
a = 6.272 (2) Å | Cu Kα radiation, λ = 1.54180 Å |
b = 10.687 (3) Å | Cell parameters from 25 reflections |
c = 15.327 (4) Å | θ = 9.2–19.1° |
α = 103.39 (2)° | µ = 0.59 mm−1 |
β = 87.79 (3)° | T = 293 K |
γ = 95.62 (2)° | Prism, colourless |
V = 994.5 (5) Å3 | 0.20 × 0.20 × 0.06 mm |
Z = 2 | |
Data collection top
Enraf-Nonius CAD4 diffractometer | Rint = 0.096 |
Radiation source: fine-focus sealed tube | θmax = 67.1°, θmin = 3.0° |
Graphite monochromator | h = −7→7 |
θ/2θ scans | k = −12→12 |
7202 measured reflections | l = −18→18 |
3554 independent reflections | 3 standard reflections every 120 min |
1374 reflections with I > 2σ(I) | intensity decay: 6% |
Refinement top
Refinement on F2 | Secondary atom site location: difference Fourier map |
Least-squares matrix: full | Hydrogen site location: inferred from neighbouring sites |
R[F2 > 2σ(F2)] = 0.083 | H-atom parameters constrained |
wR(F2) = 0.218 | Calculated w = 1/[σ2(Fo2) + (0.1516P)2] where P = (Fo2 + 2Fc2)/3 |
S = 0.97 | (Δ/σ)max = 0.005 |
3548 reflections | Δρmax = 0.23 e Å−3 |
236 parameters | Δρmin = −0.27 e Å−3 |
0 restraints | Extinction correction: SHELXL93 (Sheldrick, 1993), Fc*=kFc[1+0.001xFc2λ3/sin(2θ)]-1/4 |
Primary atom site location: structure-invariant direct methods | Extinction coefficient: 0.0005 (9) |
Crystal data top
C22H26N2O2 | γ = 95.62 (2)° |
Mr = 350.45 | V = 994.5 (5) Å3 |
Triclinic, P1 | Z = 2 |
a = 6.272 (2) Å | Cu Kα radiation |
b = 10.687 (3) Å | µ = 0.59 mm−1 |
c = 15.327 (4) Å | T = 293 K |
α = 103.39 (2)° | 0.20 × 0.20 × 0.06 mm |
β = 87.79 (3)° | |
Data collection top
Enraf-Nonius CAD4 diffractometer | Rint = 0.096 |
7202 measured reflections | 3 standard reflections every 120 min |
3554 independent reflections | intensity decay: 6% |
1374 reflections with I > 2σ(I) | |
Refinement top
R[F2 > 2σ(F2)] = 0.083 | 0 restraints |
wR(F2) = 0.218 | H-atom parameters constrained |
S = 0.97 | Δρmax = 0.23 e Å−3 |
3548 reflections | Δρmin = −0.27 e Å−3 |
236 parameters | |
Special details top
Geometry. All e.s.d.'s (except the e.s.d. in the dihedral angle between two l.s. planes)
are estimated using the full covariance matrix. The cell e.s.d.'s are taken
into account individually in the estimation of e.s.d.'s in distances, angles
and torsion angles; correlations between e.s.d.'s in cell parameters are only
used when they are defined by crystal symmetry. An approximate (isotropic)
treatment of cell e.s.d.'s is used for estimating e.s.d.'s involving l.s.
planes. |
Refinement. Refinement on F2 for ALL reflections except for 6 with very negative
F2 or flagged by the user for potential systematic errors. Weighted
R-factors wR and all goodnesses of fit S are based on
F2, conventional R-factors R are based on F,
with F set to zero for negative F2. The observed criterion of
F2 > σ(F2) is used only for calculating _R_factor_obs
etc. and is not relevant to the choice of reflections for refinement.
R-factors based on F2 are statistically about twice as large
as those based on F, and R- factors based on ALL data will be
even larger. |
Fractional atomic coordinates and isotropic or equivalent isotropic displacement parameters (Å2) top | x | y | z | Uiso*/Ueq | |
C1 | −0.1994 (8) | 0.4347 (5) | 0.2131 (4) | 0.0619 (15) | |
N2 | −0.0159 (6) | 0.4667 (4) | 0.1686 (3) | 0.0542 (11) | |
C3 | 0.1080 (8) | 0.3741 (5) | 0.1980 (4) | 0.0601 (14) | |
H3A | 0.2347 | 0.4136 | 0.2317 | 0.072* | |
H3B | 0.1414 | 0.3012 | 0.1504 | 0.072* | |
C4 | −0.0863 (7) | 0.3453 (5) | 0.2568 (4) | 0.0580 (14) | |
O5 | −0.1724 (6) | 0.2143 (3) | 0.2375 (2) | 0.0768 (12) | |
N6 | −0.2273 (7) | 0.1752 (4) | 0.3217 (3) | 0.0590 (12) | |
C7 | −0.2437 (8) | 0.2973 (5) | 0.3904 (4) | 0.0607 (15) | |
H7 | −0.3840 | 0.3290 | 0.3873 | 0.073* | |
C8 | −0.0689 (9) | 0.3857 (5) | 0.3569 (4) | 0.069 (2) | |
H8A | −0.0944 | 0.4757 | 0.3787 | 0.083* | |
H8B | 0.0714 | 0.3727 | 0.3760 | 0.083* | |
O9 | −0.3749 (6) | 0.4733 (4) | 0.2176 (3) | 0.098 (2) | |
C10 | 0.0466 (8) | 0.5618 (5) | 0.1223 (3) | 0.0502 (12) | |
C11 | 0.2539 (8) | 0.5742 (5) | 0.0904 (3) | 0.0611 (14) | |
H11 | 0.3499 | 0.5163 | 0.0972 | 0.073* | |
C12 | 0.3184 (9) | 0.6717 (6) | 0.0488 (4) | 0.070 (2) | |
H12 | 0.4599 | 0.6793 | 0.0287 | 0.084* | |
C13 | 0.1829 (10) | 0.7597 (5) | 0.0351 (4) | 0.068 (2) | |
C14 | −0.0235 (9) | 0.7441 (5) | 0.0671 (4) | 0.068 (2) | |
H14 | −0.1196 | 0.8017 | 0.0597 | 0.082* | |
C15 | −0.0939 (9) | 0.6480 (5) | 0.1094 (4) | 0.0637 (15) | |
H15 | −0.2354 | 0.6405 | 0.1294 | 0.076* | |
C16 | 0.2563 (12) | 0.8674 (6) | −0.0087 (5) | 0.104 (2) | |
H16A | 0.4043 | 0.8621 | −0.0264 | 0.156* | |
H16B | 0.2404 | 0.9485 | 0.0327 | 0.156* | |
H16C | 0.1716 | 0.8611 | −0.0607 | 0.156* | |
C17 | −0.2068 (9) | 0.2848 (5) | 0.4837 (4) | 0.0616 (15) | |
C18 | −0.0380 (11) | 0.2271 (6) | 0.5033 (5) | 0.085 (2) | |
H18 | 0.0546 | 0.1917 | 0.4573 | 0.102* | |
C19 | −0.0003 (14) | 0.2197 (8) | 0.5889 (6) | 0.107 (2) | |
H19 | 0.1201 | 0.1825 | 0.6007 | 0.128* | |
C20 | −0.1362 (18) | 0.2657 (8) | 0.6565 (5) | 0.111 (3) | |
H20 | −0.1110 | 0.2584 | 0.7144 | 0.133* | |
C21 | −0.3094 (15) | 0.3227 (7) | 0.6399 (5) | 0.100 (3) | |
H21 | −0.4027 | 0.3545 | 0.6867 | 0.120* | |
C22 | −0.3485 (10) | 0.3340 (5) | 0.5527 (5) | 0.083 (2) | |
H22 | −0.4666 | 0.3736 | 0.5411 | 0.099* | |
C23 | −0.4174 (9) | 0.0828 (5) | 0.3031 (4) | 0.064 (2) | |
C24 | −0.4862 (12) | 0.0422 (6) | 0.3885 (4) | 0.106 (3) | |
H24A | −0.3691 | 0.0079 | 0.4108 | 0.159* | |
H24B | −0.6051 | −0.0228 | 0.3766 | 0.159* | |
H24C | −0.5284 | 0.1156 | 0.4324 | 0.159* | |
C25 | −0.3510 (12) | −0.0330 (6) | 0.2315 (4) | 0.107 (3) | |
H25A | −0.3077 | −0.0055 | 0.1776 | 0.160* | |
H25B | −0.4700 | −0.0978 | 0.2191 | 0.160* | |
H25C | −0.2336 | −0.0683 | 0.2529 | 0.160* | |
C26 | −0.6016 (11) | 0.1379 (8) | 0.2661 (5) | 0.113 (3) | |
H26A | −0.5553 | 0.1633 | 0.2118 | 0.169* | |
H26B | −0.6442 | 0.2117 | 0.3095 | 0.169* | |
H26C | −0.7209 | 0.0733 | 0.2538 | 0.169* | |
Atomic displacement parameters (Å2) top | U11 | U22 | U33 | U12 | U13 | U23 |
C1 | 0.042 (3) | 0.071 (4) | 0.072 (4) | −0.002 (3) | 0.005 (3) | 0.020 (3) |
N2 | 0.041 (2) | 0.061 (3) | 0.065 (3) | 0.006 (2) | 0.007 (2) | 0.025 (2) |
C3 | 0.050 (3) | 0.067 (3) | 0.074 (4) | 0.004 (3) | 0.000 (3) | 0.037 (3) |
C4 | 0.049 (3) | 0.053 (3) | 0.074 (4) | −0.012 (2) | 0.004 (3) | 0.026 (3) |
O5 | 0.091 (3) | 0.064 (2) | 0.068 (3) | −0.027 (2) | 0.010 (2) | 0.017 (2) |
N6 | 0.061 (3) | 0.051 (2) | 0.064 (3) | 0.000 (2) | 0.016 (2) | 0.016 (2) |
C7 | 0.061 (3) | 0.046 (3) | 0.074 (4) | 0.001 (2) | 0.004 (3) | 0.016 (3) |
C8 | 0.069 (4) | 0.059 (3) | 0.077 (4) | −0.011 (3) | −0.001 (3) | 0.018 (3) |
O9 | 0.046 (2) | 0.115 (3) | 0.145 (4) | 0.015 (2) | 0.021 (2) | 0.054 (3) |
C10 | 0.049 (3) | 0.052 (3) | 0.052 (3) | −0.002 (2) | 0.005 (2) | 0.021 (3) |
C11 | 0.053 (3) | 0.064 (3) | 0.068 (4) | 0.003 (3) | 0.012 (3) | 0.021 (3) |
C12 | 0.055 (3) | 0.090 (4) | 0.067 (4) | −0.014 (3) | 0.002 (3) | 0.029 (3) |
C13 | 0.084 (4) | 0.062 (3) | 0.058 (4) | −0.016 (3) | −0.011 (3) | 0.022 (3) |
C14 | 0.079 (4) | 0.057 (3) | 0.072 (4) | 0.009 (3) | −0.006 (3) | 0.021 (3) |
C15 | 0.055 (3) | 0.070 (4) | 0.070 (4) | 0.007 (3) | 0.003 (3) | 0.023 (3) |
C16 | 0.138 (6) | 0.083 (4) | 0.099 (5) | −0.018 (4) | 0.005 (5) | 0.052 (4) |
C17 | 0.067 (4) | 0.053 (3) | 0.061 (4) | −0.010 (3) | 0.005 (3) | 0.013 (3) |
C18 | 0.083 (5) | 0.100 (5) | 0.075 (5) | 0.009 (4) | −0.004 (4) | 0.024 (4) |
C19 | 0.125 (7) | 0.116 (6) | 0.086 (6) | 0.001 (5) | −0.031 (5) | 0.032 (5) |
C20 | 0.170 (9) | 0.086 (6) | 0.064 (5) | −0.049 (6) | −0.011 (6) | 0.015 (4) |
C21 | 0.140 (7) | 0.063 (4) | 0.074 (5) | −0.034 (4) | 0.038 (5) | −0.005 (4) |
C22 | 0.087 (4) | 0.061 (4) | 0.091 (5) | −0.012 (3) | 0.026 (4) | 0.012 (4) |
C23 | 0.078 (4) | 0.041 (3) | 0.072 (4) | −0.005 (3) | 0.010 (3) | 0.016 (3) |
C24 | 0.144 (6) | 0.072 (4) | 0.088 (5) | −0.049 (4) | 0.023 (4) | 0.020 (4) |
C25 | 0.151 (7) | 0.057 (4) | 0.100 (6) | −0.004 (4) | 0.014 (5) | 0.003 (4) |
C26 | 0.082 (5) | 0.116 (6) | 0.131 (7) | −0.012 (4) | −0.015 (5) | 0.016 (5) |
Geometric parameters (Å, º) top
C1—O9 | 1.207 (6) | C11—C12 | 1.364 (7) |
C1—N2 | 1.370 (6) | C12—C13 | 1.383 (8) |
C1—C4 | 1.527 (7) | C13—C14 | 1.376 (7) |
N2—C10 | 1.388 (6) | C13—C16 | 1.489 (7) |
N2—C3 | 1.473 (6) | C14—C15 | 1.366 (7) |
C3—C4 | 1.537 (6) | C17—C18 | 1.353 (8) |
C4—O5 | 1.418 (5) | C17—C22 | 1.395 (7) |
C4—C8 | 1.500 (7) | C18—C19 | 1.363 (9) |
O5—N6 | 1.465 (5) | C19—C20 | 1.349 (10) |
N6—C23 | 1.464 (6) | C20—C21 | 1.355 (10) |
N6—C7 | 1.485 (6) | C21—C22 | 1.404 (10) |
C7—C8 | 1.528 (6) | C23—C24 | 1.507 (7) |
C7—C17 | 1.495 (7) | C23—C26 | 1.530 (9) |
C10—C11 | 1.376 (6) | C23—C25 | 1.532 (8) |
C10—C15 | 1.386 (7) | | |
| | | |
O9—C1—N2 | 131.3 (5) | C15—C10—N2 | 121.4 (4) |
O9—C1—C4 | 136.4 (5) | C12—C11—C10 | 119.9 (5) |
N2—C1—C4 | 92.1 (4) | C11—C12—C13 | 123.0 (5) |
C1—N2—C10 | 134.4 (4) | C14—C13—C12 | 115.7 (5) |
C1—N2—C3 | 94.0 (4) | C14—C13—C16 | 121.8 (6) |
C10—N2—C3 | 131.1 (4) | C12—C13—C16 | 122.5 (6) |
N2—C3—C4 | 87.9 (4) | C15—C14—C13 | 123.0 (5) |
O5—C4—C8 | 106.0 (4) | C14—C15—C10 | 119.7 (5) |
C8—C4—C3 | 119.1 (4) | C18—C17—C22 | 118.8 (6) |
O5—C4—C1 | 115.5 (4) | C18—C17—C7 | 121.6 (6) |
C1—C4—C3 | 85.5 (4) | C22—C17—C7 | 119.6 (6) |
C8—C4—C1 | 115.6 (4) | C17—C18—C19 | 121.6 (7) |
O5—C4—C3 | 114.6 (4) | C20—C19—C18 | 120.6 (8) |
C4—O5—N6 | 109.3 (4) | C19—C20—C21 | 120.0 (8) |
O5—N6—C23 | 105.8 (4) | C20—C21—C22 | 120.3 (8) |
C23—N6—C7 | 118.7 (4) | C17—C22—C21 | 118.7 (7) |
O5—N6—C7 | 105.5 (4) | N6—C23—C24 | 108.3 (5) |
N6—C7—C17 | 113.3 (4) | N6—C23—C26 | 112.6 (5) |
N6—C7—C8 | 100.7 (4) | C24—C23—C26 | 110.5 (6) |
C8—C7—C17 | 112.8 (4) | N6—C23—C25 | 106.8 (5) |
C4—C8—C7 | 103.6 (4) | C24—C23—C25 | 110.6 (5) |
C11—C10—C15 | 118.7 (5) | C26—C23—C25 | 108.0 (6) |
C11—C10—N2 | 119.9 (5) | | |
| | | |
O9—C1—N2—C10 | 8.9 (11) | C1—N2—C10—C15 | −3.3 (9) |
C4—C1—N2—C10 | −166.8 (6) | C3—N2—C10—C15 | −173.2 (5) |
O9—C1—N2—C3 | −178.7 (7) | C15—C10—C11—C12 | 1.4 (8) |
C4—C1—N2—C3 | 5.6 (4) | N2—C10—C11—C12 | −176.7 (5) |
C1—N2—C3—C4 | −5.5 (4) | C10—C11—C12—C13 | −1.2 (9) |
C10—N2—C3—C4 | 167.2 (5) | C11—C12—C13—C14 | 0.7 (9) |
O9—C1—C4—O5 | 64.1 (9) | C11—C12—C13—C16 | 178.7 (6) |
N2—C1—C4—O5 | −120.5 (4) | C12—C13—C14—C15 | −0.5 (9) |
O9—C1—C4—C8 | −60.4 (9) | C16—C13—C14—C15 | −178.4 (6) |
N2—C1—C4—C8 | 115.0 (4) | C13—C14—C15—C10 | 0.7 (9) |
O9—C1—C4—C3 | 179.3 (7) | C11—C10—C15—C14 | −1.2 (8) |
N2—C1—C4—C3 | −5.3 (4) | N2—C10—C15—C14 | 176.9 (5) |
N2—C3—C4—O5 | 121.0 (5) | N6—C7—C17—C18 | 47.8 (7) |
N2—C3—C4—C8 | −112.0 (5) | C8—C7—C17—C18 | −65.7 (7) |
N2—C3—C4—C1 | 5.0 (4) | N6—C7—C17—C22 | −132.5 (5) |
C8—C4—O5—N6 | 5.0 (5) | C8—C7—C17—C22 | 113.9 (5) |
C1—C4—O5—N6 | −124.4 (5) | C22—C17—C18—C19 | −2.0 (10) |
C3—C4—O5—N6 | 138.5 (4) | C7—C17—C18—C19 | 177.7 (6) |
C4—O5—N6—C23 | 146.3 (4) | C17—C18—C19—C20 | 2.5 (12) |
C4—O5—N6—C7 | 19.6 (5) | C18—C19—C20—C21 | −1.5 (12) |
O5—N6—C7—C17 | −155.6 (4) | C19—C20—C21—C22 | 0.1 (11) |
O5—N6—C7—C8 | −34.9 (5) | C18—C17—C22—C21 | 0.5 (8) |
C23—N6—C7—C17 | 86.0 (6) | C7—C17—C22—C21 | −179.2 (5) |
C23—N6—C7—C8 | −153.2 (5) | C20—C21—C22—C17 | 0.4 (9) |
O5—C4—C8—C7 | −26.9 (5) | O5—N6—C23—C24 | −178.1 (4) |
C1—C4—C8—C7 | 102.4 (5) | C7—N6—C23—C24 | −60.0 (6) |
C3—C4—C8—C7 | −157.9 (4) | O5—N6—C23—C26 | −55.6 (6) |
N6—C7—C8—C4 | 37.7 (5) | C7—N6—C23—C26 | 62.5 (7) |
C17—C7—C8—C4 | 158.8 (5) | O5—N6—C23—C25 | 62.8 (5) |
C1—N2—C10—C11 | 174.8 (5) | C7—N6—C23—C25 | −179.1 (5) |
C3—N2—C10—C11 | 4.9 (8) | | |
Experimental details
| (III) | (IV) |
Crystal data |
Chemical formula | C25H22N2O4 | C22H26N2O2 |
Mr | 414.45 | 350.45 |
Crystal system, space group | Monoclinic, P21/n | Triclinic, P1 |
Temperature (K) | 293 | 293 |
a, b, c (Å) | 9.368 (5), 19.776 (7), 11.484 (8) | 6.272 (2), 10.687 (3), 15.327 (4) |
α, β, γ (°) | 90, 101.92 (4), 90 | 103.39 (2), 87.79 (3), 95.62 (2) |
V (Å3) | 2082 (2) | 994.5 (5) |
Z | 4 | 2 |
Radiation type | Cu Kα | Cu Kα |
µ (mm−1) | 0.74 | 0.59 |
Crystal size (mm) | 0.36 × 0.20 × 0.13 | 0.20 × 0.20 × 0.06 |
|
Data collection |
Diffractometer | Enraf-Nonius CAD4 diffractometer | Enraf-Nonius CAD4 diffractometer |
Absorption correction | – | – |
No. of measured, independent and observed [I > 2σ(I)] reflections | 6167, 3711, 2276 | 7202, 3554, 1374 |
Rint | 0.043 | 0.096 |
(sin θ/λ)max (Å−1) | 0.597 | 0.598 |
|
Refinement |
R[F2 > 2σ(F2)], wR(F2), S | 0.050, 0.120, 1.01 | 0.083, 0.218, 0.97 |
No. of reflections | 3711 | 3548 |
No. of parameters | 282 | 236 |
H-atom treatment | H atoms treated by a mixture of independent and constrained refinement | H-atom parameters constrained |
Δρmax, Δρmin (e Å−3) | 0.21, −0.19 | 0.23, −0.27 |
Selected geometric parameters (Å, º) for (III) topC1—O9 | 1.212 (3) | C4—O5 | 1.438 (3) |
C1—N2 | 1.361 (3) | O5—N6 | 1.452 (2) |
C1—C4 | 1.548 (3) | N6—C7 | 1.474 (3) |
N2—C10 | 1.408 (3) | C7—C8 | 1.520 (3) |
N2—C3 | 1.475 (3) | C4—C8 | 1.527 (3) |
C3—C4 | 1.532 (3) | | |
| | | |
N2—C1—C4 | 90.9 (2) | N2—C3—C4 | 87.4 (2) |
C1—N2—C3 | 95.5 (2) | C1—C4—C3 | 86.0 (2) |
| | | |
O9—C1—N2—C10 | 15.1 (4) | O5—C4—C8—C7 | 11.2 (2) |
N2—C3—C4—O5 | 120.4 (2) | C3—N2—C10—C11 | 5.8 (4) |
N2—C3—C4—C8 | −115.1 (2) | C1—N2—C10—C15 | −10.5 (4) |
C8—C4—O5—N6 | 13.5 (2) | C12—C13—O16—C17 | −22.1 (5) |
C4—O5—N6—C26 | 91.6 (2) | C8—C7—C18—O19 | −12.7 (3) |
C4—O5—N6—C7 | −33.3 (2) | O19—C18—C20—C21 | 0.9 (4) |
O5—N6—C7—C8 | 39.5 (2) | O5—N6—C26—C27 | −165.0 (2) |
N6—C7—C8—C4 | −31.3 (2) | | |
Selected geometric parameters (Å, º) for (IV) topC1—O9 | 1.207 (6) | C4—O5 | 1.418 (5) |
C1—N2 | 1.370 (6) | C4—C8 | 1.500 (7) |
C1—C4 | 1.527 (7) | O5—N6 | 1.465 (5) |
N2—C10 | 1.388 (6) | N6—C7 | 1.485 (6) |
N2—C3 | 1.473 (6) | C7—C8 | 1.528 (6) |
C3—C4 | 1.537 (6) | | |
| | | |
N2—C1—C4 | 92.1 (4) | N2—C3—C4 | 87.9 (4) |
C1—N2—C3 | 94.0 (4) | C1—C4—C3 | 85.5 (4) |
| | | |
O9—C1—N2—C10 | 8.9 (11) | O5—N6—C7—C8 | −34.9 (5) |
N2—C3—C4—O5 | 121.0 (5) | N6—C7—C8—C4 | 37.7 (5) |
N2—C3—C4—C8 | −112.0 (5) | C3—N2—C10—C11 | 4.9 (8) |
C8—C4—O5—N6 | 5.0 (5) | C1—N2—C10—C15 | −3.3 (9) |
C4—O5—N6—C23 | 146.3 (4) | C8—C7—C17—C18 | −65.7 (7) |
C4—O5—N6—C7 | 19.6 (5) | O5—N6—C23—C24 | −178.1 (4) |
Spirocompounds which incorporate highly strained methylenelactam moieties were unknown compounds at the begining of our work. In a preliminary communication (Rigolet et al., 1998), it was shown that 1,3-dipolar cycloaddition of nitrones and 3-methylene isoindolones proceeded with low stereoselectivity. Nevertheless, complete stereospecificity was possible when 3-methylene azetidin-2-ones, (I), were reacted as dipolarophiles. The present X-ray study was undertaken to elucidate the geometry of the title bicyclic adducts, (III) and (IV). The structures are depicted with the atom-labelling schemes in Fig. 1 and Fig. 2, respectively. \scheme
In both (III) and (IV), the lactam ring (2-azetidinone) is planar [maximum deviation 0.027 (2) Å for (III) and 0.045 (3) Å for (IV)] and is conjugated with the p-methoxyphenyl or p-methylphenyl substituent at N2. The dihedral angle between the two best mean planes (phenyl/azetidinone) is 16.7 (2)° in (III) and 12.2 (4)° in (IV). The folding occurs at atom N2 which appears slightly tetrahedral, being 0.101 (2) Å and 0.054 (5) Å out of the plane of atoms C3, C1 and C10 in (III) and (IV), respectively.
The conformations of the two molecules differ essentially by the conformations of the isoxazolidine rings. These five-membered rings adopt a different envelope conformation, where C7 is displaced by -0.542 (3) Å in (III) and 0.580 (8) Å in (IV) out of the best mean plane passing through atoms O5, C4, C8 and N6, the sign of the displacement being correlated with the positive distance of O9 from the mean plane. The substituents at N6 and C7 are pseudo-axial in (III) and pseudo-equatorial in (IV). The possible transition state of the cycloaddition process may be clearly depicted from this structure.