Supporting information
Crystallographic Information File (CIF) https://doi.org/10.1107/S1600536802016689/dn6039sup1.cif | |
Structure factor file (CIF format) https://doi.org/10.1107/S1600536802016689/dn6039Isup2.hkl |
CCDC reference: 198965
To a suspension of activated magnesium turnings (3.25 mmol) in dry Et2O was added 1,2-dibromoethane (3.25 mmol). The resulting mixture was stirred until all magnesium turnings disappeared, and the solvent was evaporated under an N2 draught. After addition of dry CH2Cl2 (10 ml), (4S)-3-acryloyl-4-benzyl-1,3-oxazolidin-2-one (1.10 mmol) in anhydrous CH2Cl2 (3 ml) was added at 263 K. After stirring at 263 K for 15 min, dimethyl (2E)-[(dimethylamino)methylene]-3-thiosuccinate (1.10 mmol) was slowly added. The reaction mixture was then stirred at 263 K for 3 h. Saturated NaHCO3 (5 ml) was added and the organic layer was washed with saturated NaHCO3 (2 x 5 ml), water (5 ml) and brine (5 ml). The CH2Cl2 extract was then dried over anhydrous MgSO4, filtered and concentrated. The crude mixture was flash-chromatographed on silica (eluent: petroleum ether/AcOEt, 7:3) to afford (I) (285 mg, 57%) along with one other diastereoisomer (142 mg, 28%). Single crystals of (I) suitable for X-ray analysis were obtained by crystallization from AcOEt/petroleum ether.
All non-H atoms were refined with anisotropic atomic displacement parameters. Orientation of the CH3 groups was determined from difference Fourier syntheses and initially refined as rigid bodies. All H atoms were then fixed at calculated and/or refined positions. A riding isotropic displacement parameter was used for all hydrogen atoms. The absolute configuration was unambiguously determined by refining the Flack enantiopole parameter using 1994 Friedel pairs.
Data collection: Collect (Nonius, 1998); cell refinement: HKL SCALEPACK; data reduction: HKL DENZO and SCALEPACK (Otwinowski & Minor 1997); program(s) used to solve structure: SHELXTL (Sheldrick, 1995); program(s) used to refine structure: JANA2000 (Petricek & Dusek, 2000); molecular graphics: DIAMOND (Brandenburg & Berndt, 1999); software used to prepare material for publication: JANA2000.
Fig. 1. The molecular structure of (I), showing 50% probability displacement ellipsoids. H are omitted for clarity. |
C22H26N2O7S | F(000) = 976 |
Mr = 462.5 | Dx = 1.358 (1) Mg m−3 |
Orthorhombic, P212121 | Mo Kα radiation, λ = 0.71069 Å |
Hall symbol: P 2ac 2ab | Cell parameters from 14696 reflections |
a = 6.1205 (1) Å | θ = 2.9–26.7° |
b = 16.1195 (4) Å | µ = 0.19 mm−1 |
c = 22.9272 (6) Å | T = 150 K |
V = 2261.98 (9) Å3 | Needle, colourless |
Z = 4 | 0.4 × 0.03 × 0.03 mm |
Nonius KappaCCD diffractometer | 3833 reflections with I > 2σ(I) |
Horizonally mounted graphite crystal monochromator | Rint = 0.063 |
Detector resolution: 9 pixels mm-1 | θmax = 26.7°, θmin = 3.0° |
ϕ and ω scans | h = −7→6 |
22365 measured reflections | k = −20→20 |
4753 independent reflections | l = −28→28 |
Refinement on F2 | (Δ/σ)max = 0.0003 |
R[F2 > 2σ(F2)] = 0.043 | Δρmax = 0.76 e Å−3 |
wR(F2) = 0.088 | Δρmin = −0.40 e Å−3 |
S = 1.23 | Extinction correction: B-C type 1 Lorentzian isotropic (Becker & Coppens, 1974) |
4753 reflections | Extinction coefficient: 1.5 (2) |
290 parameters | Absolute structure: Flack (1983) |
H-atom parameters not refined | Absolute structure parameter: 0.00 (8) |
Weighting scheme based on measured s.u.'s w = 1/[σ2(I) + 0.001296I2] |
C22H26N2O7S | V = 2261.98 (9) Å3 |
Mr = 462.5 | Z = 4 |
Orthorhombic, P212121 | Mo Kα radiation |
a = 6.1205 (1) Å | µ = 0.19 mm−1 |
b = 16.1195 (4) Å | T = 150 K |
c = 22.9272 (6) Å | 0.4 × 0.03 × 0.03 mm |
Nonius KappaCCD diffractometer | 3833 reflections with I > 2σ(I) |
22365 measured reflections | Rint = 0.063 |
4753 independent reflections |
R[F2 > 2σ(F2)] = 0.043 | H-atom parameters not refined |
wR(F2) = 0.088 | Δρmax = 0.76 e Å−3 |
S = 1.23 | Δρmin = −0.40 e Å−3 |
4753 reflections | Absolute structure: Flack (1983) |
290 parameters | Absolute structure parameter: 0.00 (8) |
x | y | z | Uiso*/Ueq | ||
S1 | 0.65977 (10) | 0.24954 (4) | 0.58687 (2) | 0.03101 (18) | |
O1 | 1.0275 (2) | 0.24942 (11) | 0.67157 (7) | 0.0330 (5) | |
O2 | 0.7764 (3) | 0.24146 (11) | 0.74256 (7) | 0.0419 (6) | |
O3 | 0.4552 (3) | 0.42098 (11) | 0.75962 (7) | 0.0416 (6) | |
O4 | 0.8120 (3) | 0.42069 (10) | 0.73764 (7) | 0.0346 (5) | |
O5 | 0.0474 (3) | 0.43346 (11) | 0.55260 (7) | 0.0331 (5) | |
O6 | 0.5974 (2) | 0.39058 (10) | 0.44840 (7) | 0.0288 (5) | |
O7 | 0.3752 (2) | 0.44087 (9) | 0.38016 (6) | 0.0300 (5) | |
N1 | 0.4240 (3) | 0.51056 (10) | 0.62651 (8) | 0.0266 (6) | |
N2 | 0.2516 (3) | 0.44179 (10) | 0.47143 (7) | 0.0211 (5) | |
C1 | 0.6838 (4) | 0.30598 (13) | 0.65181 (9) | 0.0232 (6) | |
C2 | 0.5706 (3) | 0.37440 (13) | 0.66589 (9) | 0.0215 (6) | |
C3 | 0.4053 (3) | 0.41930 (12) | 0.62726 (9) | 0.0221 (6) | |
C4 | 0.4179 (3) | 0.38923 (12) | 0.56409 (9) | 0.0211 (6) | |
C5 | 0.4115 (4) | 0.29436 (13) | 0.55889 (9) | 0.0268 (7) | |
C6 | 0.8311 (4) | 0.26296 (13) | 0.69466 (10) | 0.0259 (7) | |
C7 | 1.1805 (4) | 0.20477 (17) | 0.70814 (12) | 0.0442 (9) | |
C8 | 0.6004 (4) | 0.40785 (13) | 0.72597 (10) | 0.0264 (7) | |
C9 | 0.8661 (5) | 0.44372 (18) | 0.79658 (12) | 0.0503 (10) | |
C10 | 0.6446 (4) | 0.54365 (13) | 0.62428 (11) | 0.0357 (8) | |
C11 | 0.2850 (4) | 0.55502 (15) | 0.66718 (12) | 0.0397 (8) | |
C12 | 0.2254 (4) | 0.42336 (13) | 0.53065 (9) | 0.0222 (6) | |
C13 | 0.4264 (4) | 0.42150 (13) | 0.43551 (9) | 0.0230 (7) | |
C14 | 0.1481 (4) | 0.46520 (13) | 0.37559 (10) | 0.0296 (7) | |
C15 | 0.0686 (4) | 0.47803 (13) | 0.43826 (9) | 0.0264 (7) | |
C16 | 0.0247 (4) | 0.56882 (15) | 0.45392 (10) | 0.0311 (8) | |
C17 | 0.2129 (4) | 0.62708 (13) | 0.44358 (10) | 0.0293 (7) | |
C18 | 0.3805 (4) | 0.63447 (13) | 0.48435 (10) | 0.0293 (7) | |
C19 | 0.5533 (4) | 0.68855 (14) | 0.47556 (11) | 0.0344 (8) | |
C20 | 0.5623 (5) | 0.73578 (14) | 0.42505 (11) | 0.0397 (8) | |
C21 | 0.3983 (5) | 0.72937 (14) | 0.38425 (11) | 0.0426 (9) | |
C22 | 0.2249 (4) | 0.67556 (14) | 0.39350 (10) | 0.0344 (8) | |
H3 | 0.2637 | 0.4078 | 0.6454 | 0.026* | |
H4 | 0.5569 | 0.4089 | 0.5479 | 0.025* | |
H5a | 0.3896 | 0.2828 | 0.5174 | 0.032* | |
H5b | 0.282 | 0.2769 | 0.5809 | 0.032* | |
H7a | 1.2327 | 0.2403 | 0.7395 | 0.053* | |
H7b | 1.1156 | 0.1552 | 0.7246 | 0.053* | |
H7c | 1.3022 | 0.1896 | 0.6832 | 0.053* | |
H9a | 1.0225 | 0.4526 | 0.7973 | 0.06* | |
H9b | 0.7913 | 0.4947 | 0.8067 | 0.06* | |
H9c | 0.8277 | 0.4007 | 0.8245 | 0.06* | |
H10a | 0.7382 | 0.5107 | 0.5992 | 0.043* | |
H10b | 0.6362 | 0.5999 | 0.6094 | 0.053* | |
H10c | 0.7047 | 0.5446 | 0.6635 | 0.043* | |
H11a | 0.2753 | 0.612 | 0.6539 | 0.048* | |
H11b | 0.3407 | 0.5538 | 0.7068 | 0.048* | |
H11c | 0.141 | 0.5298 | 0.6662 | 0.048* | |
H14a | 0.0659 | 0.421 | 0.356 | 0.035* | |
H14b | 0.1376 | 0.5163 | 0.3528 | 0.035* | |
H15 | −0.0717 | 0.4514 | 0.4471 | 0.032* | |
H16a | −0.0989 | 0.5885 | 0.4306 | 0.037* | |
H16b | −0.0128 | 0.5718 | 0.4955 | 0.037* | |
H18 | 0.3768 | 0.6008 | 0.5198 | 0.035* | |
H19 | 0.6686 | 0.6934 | 0.505 | 0.041* | |
H20 | 0.6848 | 0.7737 | 0.4182 | 0.048* | |
H21 | 0.4044 | 0.7631 | 0.3488 | 0.051* | |
H22 | 0.11 | 0.6717 | 0.364 | 0.041* |
U11 | U22 | U33 | U12 | U13 | U23 | |
S1 | 0.0457 (4) | 0.0271 (3) | 0.0203 (3) | 0.0118 (3) | −0.0042 (3) | −0.0060 (2) |
O1 | 0.0281 (8) | 0.0411 (9) | 0.0299 (8) | 0.0105 (8) | 0.0025 (7) | 0.0078 (8) |
O2 | 0.0407 (10) | 0.0575 (11) | 0.0275 (9) | 0.0126 (9) | 0.0058 (8) | 0.0158 (8) |
O3 | 0.0392 (10) | 0.0620 (12) | 0.0236 (9) | 0.0157 (9) | −0.0013 (9) | −0.0138 (8) |
O4 | 0.0324 (9) | 0.0452 (10) | 0.0261 (9) | −0.0015 (8) | −0.0076 (7) | −0.0094 (7) |
O5 | 0.0240 (8) | 0.0487 (10) | 0.0265 (9) | 0.0014 (8) | 0.0031 (8) | 0.0048 (8) |
O6 | 0.0210 (8) | 0.0401 (9) | 0.0253 (9) | −0.0019 (7) | 0.0014 (7) | −0.0011 (7) |
O7 | 0.0318 (9) | 0.0380 (9) | 0.0202 (8) | −0.0039 (7) | −0.0005 (7) | 0.0063 (7) |
N1 | 0.0289 (10) | 0.0202 (9) | 0.0308 (11) | 0.0034 (8) | −0.0009 (9) | −0.0036 (8) |
N2 | 0.0199 (9) | 0.0239 (10) | 0.0195 (9) | −0.0017 (8) | −0.0014 (8) | 0.0020 (7) |
C1 | 0.0259 (11) | 0.0259 (11) | 0.0178 (11) | −0.0005 (10) | 0.0030 (10) | 0.0000 (9) |
C2 | 0.0225 (11) | 0.0244 (11) | 0.0176 (11) | 0.0001 (9) | 0.0011 (10) | −0.0006 (9) |
C3 | 0.0234 (11) | 0.0215 (11) | 0.0214 (11) | 0.0004 (9) | 0.0013 (10) | −0.0001 (9) |
C4 | 0.0198 (10) | 0.0225 (11) | 0.0209 (11) | −0.0006 (9) | −0.0005 (9) | 0.0023 (9) |
C5 | 0.0376 (13) | 0.0263 (11) | 0.0166 (11) | −0.0006 (10) | −0.0041 (11) | −0.0015 (9) |
C6 | 0.0311 (12) | 0.0201 (11) | 0.0265 (12) | 0.0014 (10) | −0.0032 (10) | −0.0010 (9) |
C7 | 0.0340 (14) | 0.0545 (16) | 0.0441 (16) | 0.0144 (13) | 0.0005 (13) | 0.0111 (13) |
C8 | 0.0302 (13) | 0.0293 (12) | 0.0196 (12) | 0.0054 (10) | −0.0016 (11) | −0.0014 (9) |
C9 | 0.0493 (17) | 0.0656 (19) | 0.0362 (15) | 0.0046 (15) | −0.0146 (14) | −0.0199 (13) |
C10 | 0.0360 (13) | 0.0279 (12) | 0.0432 (15) | −0.0036 (11) | −0.0017 (12) | 0.0007 (11) |
C11 | 0.0447 (15) | 0.0319 (13) | 0.0427 (15) | 0.0108 (12) | −0.0018 (13) | −0.0093 (11) |
C12 | 0.0224 (12) | 0.0225 (11) | 0.0218 (11) | −0.0027 (9) | 0.0003 (10) | −0.0006 (9) |
C13 | 0.0250 (12) | 0.0223 (11) | 0.0218 (12) | −0.0079 (10) | −0.0001 (10) | 0.0000 (9) |
C14 | 0.0351 (13) | 0.0259 (11) | 0.0277 (13) | −0.0040 (10) | −0.0101 (11) | 0.0032 (9) |
C15 | 0.0201 (11) | 0.0337 (12) | 0.0256 (12) | −0.0027 (10) | −0.0052 (10) | 0.0070 (10) |
C16 | 0.0250 (12) | 0.0364 (13) | 0.0320 (14) | 0.0082 (11) | −0.0017 (10) | 0.0044 (11) |
C17 | 0.0330 (13) | 0.0253 (11) | 0.0297 (13) | 0.0085 (10) | 0.0030 (11) | −0.0044 (10) |
C18 | 0.0384 (14) | 0.0195 (11) | 0.0299 (13) | 0.0072 (10) | −0.0007 (11) | −0.0022 (9) |
C19 | 0.0401 (13) | 0.0237 (12) | 0.0395 (15) | 0.0036 (11) | −0.0059 (12) | −0.0082 (11) |
C20 | 0.0483 (15) | 0.0288 (13) | 0.0421 (15) | −0.0048 (12) | 0.0075 (13) | −0.0054 (11) |
C21 | 0.0641 (18) | 0.0308 (13) | 0.0330 (14) | −0.0044 (13) | 0.0044 (14) | 0.0049 (10) |
C22 | 0.0478 (15) | 0.0269 (12) | 0.0286 (13) | 0.0028 (11) | −0.0075 (12) | 0.0002 (10) |
S1—C1 | 1.751 (2) | C7—H7b | 0.969 |
S1—C5 | 1.801 (2) | C7—H7c | 0.970 |
O1—C6 | 1.332 (3) | C9—H9a | 0.968 |
O1—C7 | 1.449 (3) | C9—H9b | 0.969 |
O2—C6 | 1.199 (3) | C9—H9c | 0.973 |
O3—C8 | 1.196 (3) | C10—H10a | 0.970 |
O4—C8 | 1.339 (3) | C10—H10b | 0.970 |
O4—C9 | 1.440 (3) | C10—H10c | 0.971 |
O5—C12 | 1.211 (3) | C11—H11a | 0.969 |
O6—C13 | 1.196 (3) | C11—H11b | 0.970 |
O7—C13 | 1.344 (3) | C11—H11c | 0.971 |
O7—C14 | 1.448 (3) | C14—C15 | 1.531 (3) |
N1—C3 | 1.476 (3) | C14—H14a | 0.981 |
N1—C10 | 1.453 (3) | C14—H14b | 0.978 |
N1—C11 | 1.452 (3) | C15—C16 | 1.531 (3) |
N2—C12 | 1.399 (3) | C15—H15 | 0.981 |
N2—C13 | 1.389 (3) | C16—C17 | 1.505 (3) |
N2—C15 | 1.474 (3) | C16—H16a | 0.979 |
C1—C2 | 1.342 (3) | C16—H16b | 0.981 |
C1—C6 | 1.503 (3) | C17—C18 | 1.393 (3) |
C2—C3 | 1.527 (3) | C17—C22 | 1.391 (3) |
C2—C8 | 1.490 (3) | C18—C19 | 1.385 (3) |
C3—C4 | 1.529 (3) | C18—H18 | 0.977 |
C3—H3 | 0.979 | C19—C20 | 1.387 (4) |
C4—C5 | 1.534 (3) | C19—H19 | 0.980 |
C4—C12 | 1.510 (3) | C20—C21 | 1.376 (4) |
C4—H4 | 0.981 | C20—H20 | 0.980 |
C5—H5a | 0.979 | C21—C22 | 1.387 (4) |
C5—H5b | 0.981 | C21—H21 | 0.979 |
C7—H7a | 0.972 | C22—H22 | 0.978 |
C1—S1—C5 | 99.52 (10) | N1—C10—H10b | 107.8 |
C6—O1—C7 | 115.78 (18) | N1—C10—H10c | 109.0 |
C8—O4—C9 | 116.72 (18) | H10a—C10—H10b | 109.5 |
C13—O7—C14 | 110.81 (17) | H10a—C10—H10c | 109.5 |
C3—N1—C10 | 116.00 (17) | H10b—C10—H10c | 109.4 |
C3—N1—C11 | 116.06 (17) | N1—C11—H11a | 107.6 |
C10—N1—C11 | 112.71 (18) | N1—C11—H11b | 112.7 |
C12—N2—C13 | 127.85 (17) | N1—C11—H11c | 108.0 |
C12—N2—C15 | 119.84 (17) | H11a—C11—H11b | 109.6 |
C13—N2—C15 | 111.87 (17) | H11a—C11—H11c | 109.5 |
S1—C1—C2 | 126.02 (17) | H11b—C11—H11c | 109.4 |
S1—C1—C6 | 111.50 (15) | O5—C12—N2 | 118.55 (19) |
C2—C1—C6 | 122.12 (19) | O5—C12—C4 | 122.69 (19) |
C1—C2—C3 | 126.31 (19) | N2—C12—C4 | 118.73 (18) |
C1—C2—C8 | 117.16 (19) | O6—C13—O7 | 122.3 (2) |
C3—C2—C8 | 116.46 (18) | O6—C13—N2 | 128.7 (2) |
N1—C3—C2 | 115.35 (17) | O7—C13—N2 | 108.99 (18) |
N1—C3—C4 | 107.51 (16) | O7—C14—C15 | 105.89 (17) |
N1—C3—H3 | 105.18 | O7—C14—H14a | 109.18 |
C2—C3—C4 | 111.46 (17) | O7—C14—H14b | 109.3 |
C2—C3—H3 | 104.49 | C15—C14—H14a | 111.3 |
C4—C3—H3 | 112.80 | C15—C14—H14b | 111.50 |
C3—C4—C5 | 112.84 (17) | H14a—C14—H14b | 109.5 |
C3—C4—C12 | 109.04 (17) | N2—C15—C14 | 100.89 (17) |
C3—C4—H4 | 107.39 | N2—C15—C16 | 113.02 (18) |
C5—C4—C12 | 107.70 (17) | N2—C15—H15 | 112.66 |
C5—C4—H4 | 108.35 | C14—C15—C16 | 113.90 (18) |
C12—C4—H4 | 111.57 | C14—C15—H15 | 114.4 |
S1—C5—C4 | 110.54 (15) | C16—C15—H15 | 102.50 |
S1—C5—H5a | 112.69 | C15—C16—C17 | 115.18 (19) |
S1—C5—H5b | 112.57 | C15—C16—H16a | 108.5 |
C4—C5—H5a | 105.60 | C15—C16—H16b | 108.4 |
C4—C5—H5b | 105.44 | C17—C16—H16a | 107.6 |
H5a—C5—H5b | 109.5 | C17—C16—H16b | 107.5 |
O1—C6—O2 | 124.6 (2) | H16a—C16—H16b | 109.4 |
O1—C6—C1 | 110.93 (18) | C16—C17—C18 | 120.7 (2) |
O2—C6—C1 | 124.4 (2) | C16—C17—C22 | 121.4 (2) |
O1—C7—H7a | 110.4 | C18—C17—C22 | 117.9 (2) |
O1—C7—H7b | 111.7 | C17—C18—C19 | 121.2 (2) |
O1—C7—H7c | 106.3 | C17—C18—H18 | 119.5 |
H7a—C7—H7b | 109.4 | C19—C18—H18 | 119.2 |
H7a—C7—H7c | 109.3 | C18—C19—C20 | 119.8 (2) |
H7b—C7—H7c | 109.6 | C18—C19—H19 | 120.0 |
O3—C8—O4 | 124.3 (2) | C20—C19—H19 | 120.2 |
O3—C8—C2 | 124.7 (2) | C19—C20—C21 | 119.8 (2) |
O4—C8—C2 | 111.02 (18) | C19—C20—H20 | 120.5 |
O4—C9—H9a | 106.3 | C21—C20—H20 | 119.7 |
O4—C9—H9b | 109.6 | C20—C21—C22 | 120.1 (2) |
O4—C9—H9c | 112.3 | C20—C21—H21 | 119.7 |
H9a—C9—H9b | 109.8 | C22—C21—H21 | 120.2 |
H9a—C9—H9c | 109.4 | C17—C22—C21 | 121.2 (2) |
H9b—C9—H9c | 109.4 | C17—C22—H22 | 119.8 |
N1—C10—H10a | 111.7 | C21—C22—H22 | 119.0 |
Experimental details
Crystal data | |
Chemical formula | C22H26N2O7S |
Mr | 462.5 |
Crystal system, space group | Orthorhombic, P212121 |
Temperature (K) | 150 |
a, b, c (Å) | 6.1205 (1), 16.1195 (4), 22.9272 (6) |
V (Å3) | 2261.98 (9) |
Z | 4 |
Radiation type | Mo Kα |
µ (mm−1) | 0.19 |
Crystal size (mm) | 0.4 × 0.03 × 0.03 |
Data collection | |
Diffractometer | Nonius KappaCCD diffractometer |
Absorption correction | – |
No. of measured, independent and observed [I > 2σ(I)] reflections | 22365, 4753, 3833 |
Rint | 0.063 |
(sin θ/λ)max (Å−1) | 0.633 |
Refinement | |
R[F2 > 2σ(F2)], wR(F2), S | 0.043, 0.088, 1.23 |
No. of reflections | 4753 |
No. of parameters | 290 |
No. of restraints | ? |
H-atom treatment | H-atom parameters not refined |
Δρmax, Δρmin (e Å−3) | 0.76, −0.40 |
Absolute structure | Flack (1983) |
Absolute structure parameter | 0.00 (8) |
Computer programs: Collect (Nonius, 1998), HKL SCALEPACK, HKL DENZO and SCALEPACK (Otwinowski & Minor 1997), SHELXTL (Sheldrick, 1995), JANA2000 (Petricek & Dusek, 2000), DIAMOND (Brandenburg & Berndt, 1999), JANA2000.
Asymmetric hetero Diels-Alder reaction appears to be the method of choice for the highly efficient regio- and stereoselective synthesis of various heterocycles in enantiomerically pure form (Waldmann, 1994). In the course of an ongoing project (Trippé et al., 2002) and regarding previous results obtained in our laboratory (Marchand et al., 1995), we have isolated the substituted dihydro-2H-thiopyran resulting from the [4 + 2] cycloaddition reaction of dimethyl (2E)-[(dimethylamino)methylene]-3-thiosuccinate (Tea Gokou et al., 1985) and (4S)-3-acryloyl-4-benzyl-1,3-oxazolidin-2-one (Evans et al., 1984) in the presence of MgBr2 as catalyst. Only two diastereoisomers, in a 7/3 ratio, were obtained at the end of the reaction and separated by chromatography on SiO2. The major component is the title compound, (I), and is the result of an exo transition-state topography in the cycloaddition transition state, whereas the minor component is presumed to come from an endo approach. A full report on the synthesis as well as structural and mechanistic studies will be reported separately. Atoms O5, C12, N2, C13 and O6 are planar within less than 0.09 Å.