1H-Imidazol-1-yl 1,2,3,4-tetra­hydro­isoquinolin-2-yl ketone

In the crystal structure of the title compound, C₁₃H₁₃N₃O, the C—N_imidazole bond length of 1.431 (3) Å is shorter than that observed [1.466 (6) Å] in the corresponding carbamoyl­imidazolium salt 3-methyl-1-(1,2,3,4-tetra­hydro­isoquinolin-2-yl­carbonyl)­imidazolium iodide. A comparision of these compounds is used to highlight the structural differences that occur as a result of the imidazolium effect. Weak C—H...O hydrogen bonds link mol­ecules into extended tapes in the a direction.

S1. Comment

The increased reactivity of carbonylimidazolium salts, (II), over carbonylimidazoles, (I), has been demonstrated previously in several systems and is referred to as the imidazolium effect (Staab et al., 1998). In 1971, Oakenfull et al. established that acylimidazolium salts react with nucleophiles faster than acylimidazoles. These compounds have subsequently been of considerable synthetic interest as reactive acylating agents (Kamijo et al., 1982; Guibé-Jampel et al., 1973; Watkins & Rapoport, 1982). The higher reactivity of carbonylimidazolium salts can be attributed to the positive charge on the imidazole ring, which diminishes the electron density on the C atom of the carbonyl group, facilitating both the addition and elimination steps involved in an acyl transfer mechanism. \sch

Crystallographic analyses are known for compounds of type (I) (where R¹ is a C substituent), but a direct structural comparison between a carbonylimidazole and the corresponding carbonylimidazolium salt has not been reported. We have previously demonstrated the use of carbamoylimidazoles, (III), and carbamoylimidazolium salts, (IV), as carbamoyl transfer reagents, and used the salts (IV) for the formation of ureas, carbamates, thiocarbamates and amides (Batey et al., 1998, 2002; Batey Yoshina-Ishii et al., 1999; Grzyb & Batey, 2003). We have also previously reported the X-ray crystal structure analysis of (VI) (Batey Yoshina-Ishii & Lough, 1999). The carbamoylimidazolium salt, (VI), is prepared in two steps from 1,2,3,4-tetrahydroisoquinoline and N,N'-carbonyldiimidazole (CDI) in refluxing tetrahydrofuran to form the intermediate carbamoylimidazole, (V), in 79% yield. Methylation of (V) with iodomethane in acetonitrile at room temperature then furnishes the imidazolium salt, (VI), in 99% yield. We now report a crystal structure determination of the title carbamoylimidazole, (V), and make a direct structural comparison with the imidazolium salt, (VI), providing a structural basis of the imidazolium effect.

The C—N_isoquinoline and C—N_imidazole bond lengths in (V) are 1.344 (3) and 1.431 (3) Å, respectively. In (VI), these distances are 1.327 (6) and 1.466 (6) Å, respectively. The C—N_isoquinoline bond in both compounds is shorter than the C—N_imidazole bond, indicating that C—N_isoquinoline has more double-bond character. However, while the C—N_isoquinoline bond is longer in (V), the C—N_imidazole bond is shorter than in (VI).

The N_imidazole [atom N2 in (V)] electron pair participates in the aromatic π system of the imidazolium ring, and as a result, is not as available to contribute to the C1—N2 bond. This effect is not as strong in (V) as it is in (VI), so this bond is shorter, indicating a greater double-bond character. This stronger bond makes the imidazole in (V) a poorer leaving group.

The C═O bond length in (V) is 1.218 (3) Å, while in (VI) it is 1.211 (6) Å. While these distances are not statistically different, they correspond to the infra-red C═O stretch absorption frequencies, which are 1681 and 1711 cm⁻¹ for (V) and (VI), respectively, indicative of a stronger C═O bond in (VI) compared with (V). We have also calculated the extent of the pyramidalization of atom N1, which represents the extent of sp²/sp³ hybridization. We have defined the angle ε, which is the angle in (V) that the C—N_isoquinoline bond makes with the plane of atoms N1, C2, C10. For an ideally tetrahedral sp³ N atom, the value of ε is 35.3°, and for an sp²-hybridized N atom ε is 0°. In the case of (V), the value of ε is 5.9°, while for (VI), the value of ε is 16.2°.

Interestingly, the orientation of the imidazole rings with respect to the carbamoyl C═O group is different in (V) and (VI). Compound (V) has an s-trans relationship about the C—N_imidizole bond, whereas (VI) has an s-cis relationship. We were interested to see whether these conformational preferences were the thermodynamically preferred conformations (gas phase), and whether the same conformational preferences exist for compounds (I) and (II). Ab initio calculations (UHF/6–311G*) (SPARTAN02; Wavefunction, 2002) revealed almost identical energies (<0.1 kcal mol⁻¹; 1 kcal mol⁻¹ = 4.184 kJ mol⁻¹) for the s-cis and s-trans conformations of (I) (R¹ = CH₃). In the case of the corresponding imidazolium salt, (II) (R¹ and R² = CH₃), the s-cis conformation was 1.9 kcal mol⁻¹ lower in energy. Calculations on the carbamoylimidazole (III) [NR² = N(CH₃)₂] revealed the s-cis form to be only marginally lower in energy (0.2 kcal mol⁻¹) than the s-trans form. The solid state structure of (V) shows the compound to be in the s-trans form. However, the s-cis form is significantly lower in energy (2.1 kcal mol⁻¹) for the carbamoylimidazolium salt (IV) [NR² = N(CH₃)₂ and R² = CH₃]. This latter result correlates with the X-ray crystal structure of (VI).

In the isoquinoline group, an analysis of the puckering (Cremer & Pople, 1975) in the six-membered ring N1/C2/C3/C4/C9/C10 gives Q_T = 0.485 (3). The conformational analysis of that ring (Duax et al., 1976) shows that the conformation is half-chair, with a local psuedo-twofold axis running through the midpoints of the C2—C3 and C9—C10 bonds.

In the crystal structure of (V), molecules related by centres of symmetry are linked by C—H···O hydrogen bonds into pairs forming R₂²(10) rings (Bernstein et al., 1995). These pairs are, in turn, linked by futher C—H···O hydrogen bonds through 2₁ screw axes to form molecular tapes in the a direction. This secondary interaction involves the formation of R₄²(10) rings. Details of the hydrogen-bonding geometry and motif are given in Table 2 and Fig. 2.

S2. Experimental

The title compound was synthesized by treatment of a suspension of N,N'-carbonyldiimidazole (1.78 g, 11.0 mmol) in tetrahydrofuran (10.0 ml) with 1,2,3,4-tetrahydroisoquinoline (1.25 ml, 10.0 mmol). The mixture was refluxed for 16 h. Removal of the solvent under vacuum gave a viscous oil, which was dissolved in CH₂Cl₂ and washed twice with water. The organic layer was dried (MgSO₄), filtered and concentrated in vacuo. The crude product was recrystallized from hexane-EtOAc (Ratio?) to yield a white solid (79% yield; m.p. 355–356 K). Spectroscopic analysis: ¹H NMR (400 MHz, CDCl₃, δ, p.p.m.): 7.94 (1H, s), 7.26–7.08 (6H, m), 4.75 (2H, s), 3.82 (2H, t, J = 6.0 Hz), 3.04 (2H, t, J = 6.0 Hz); ¹³C NMR (100 MHz, CDCl₃, δ, p.p.m.): 150.8, 136.6, 133.4, 131.5, 129.5, 128.6, 127.0, 126.5, 126.0, 117.6, 48.1, 44.2, 28.3; IR (KBr pellet, ν, cm⁻¹): 3098, 2898, 1681, 1428, 1240, 1162, 1104, 1077, 1052, 933; MS (EI), m/z (relative intensity): 227 (69), 160 (100), 142 (49), 130 (10), 117 (36), 103 (14), 91 (12); high-resolution MS (EI), m/z calculated (M⁺): 227.1061; found: 227.1059.

S3. Refinement

All H atoms were placed in calculated positions, with C—H_methylene = 0.99 Å and C—H = 0.95 Å for all others. They were included in the refinement in the riding-model approximation, with U_iso(H) = 1.2U_eq(C). In the standard setting, the space group of the crystal structure is C2/c, with a β angle of 129.749 (4)°; the space group was converted to I2/a to reduce correlation among x- and z-related parameters.

Computing details

Data collection: COLLECT (Nonius, 1998); cell refinement: DENZO-SMN (Otwinowski & Minor, 1997); data reduction: DENZO-SMN; program(s) used to solve structure: SHELXTL/PC (Sheldrick, 2001); program(s) used to refine structure: SHELXTL/PC; molecular graphics: SHELXTL/PC; software used to prepare material for publication: SHELXTL/PC.

Figures

	Fig. 1. A view of the molecule of (V), with the atom-numbering scheme. Displacement ellipsoids are drawn at the 30% probability level and H atoms are shown as small spheres of arbitrary radii.
	Fig. 2. A partial packing diagram for (V), showing the C—H.·O hydrogen bonds as dashed lines.

1H-Imidazol-1-yl 1,2,3,4-tetrahydroisoquinolin-2-yl ketone

Crystal data

C13H13N3O	F(000) = 960
Mr = 227.26	Dx = 1.335 Mg m^−3
Monoclinic, I2/a	Mo Kα radiation, λ = 0.71073 Å
Hall symbol: -I 2ya	Cell parameters from 3967 reflections
a = 13.3571 (12) Å	θ = 2.6–27.5°
b = 10.7473 (10) Å	µ = 0.09 mm^−1
c = 15.7604 (15) Å	T = 150 K
β = 90.914 (4)°	Plate, colourless
V = 2262.2 (4) Å^3	0.10 × 0.10 × 0.02 mm
Z = 8

Data collection

Nonius KappaCCD area-detector diffractometer	1221 reflections with I > 2σ(I)
Radiation source: fine-focus sealed tube	Rint = 0.087
Graphite monochromator	θmax = 25.0°, θmin = 2.6°
Detector resolution: 9 pixels mm^-1	h = −15→15
ϕ scans and ω scans with κ offsets	k = −11→12
6905 measured reflections	l = −18→18
1992 independent reflections

Refinement

Refinement on F^2	Secondary atom site location: difference Fourier map
Least-squares matrix: full	Hydrogen site location: inferred from neighbouring sites
R[F^2 > 2σ(F^2)] = 0.049	H-atom parameters constrained
wR(F^2) = 0.122	w = 1/[σ^2(Fo^2) + (0.0463P)^2] where P = (Fo^2 + 2Fc^2)/3
S = 1.03	(Δ/σ)max < 0.001
1992 reflections	Δρmax = 0.21 e Å^−3
155 parameters	Δρmin = −0.27 e Å^−3
0 restraints	Extinction correction: SHELXL97 in SHELXTL/PC (Sheldrick, 2001), Fc^*=kFc[1+0.001xFc^2λ^3/sin(2θ)]^-1/4
Primary atom site location: structure-invariant direct methods	Extinction coefficient: 0.0026 (4)

Special details

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 of F² against ALL reflections. The weighted R-factor wR and goodness of fit S are based on F², conventional R-factors R are based on F, with F set to zero for negative F². The threshold expression of F² > σ(F²) is used only for calculating R-factors(gt) 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 (Ų)

	x	y	z	Uiso*/Ueq
O1	0.43786 (12)	0.10981 (15)	0.08628 (11)	0.0370 (5)
N1	0.47254 (13)	0.29472 (17)	0.15051 (12)	0.0294 (5)
N2	0.59483 (14)	0.13736 (17)	0.14241 (12)	0.0287 (5)
N3	0.73458 (15)	0.08464 (19)	0.21183 (14)	0.0396 (6)
C1	0.49508 (17)	0.1793 (2)	0.12413 (15)	0.0292 (6)
C2	0.36853 (17)	0.3374 (2)	0.14250 (17)	0.0357 (6)
H2A	0.3456	0.3687	0.1980	0.043*
H2B	0.3249	0.2669	0.1254	0.043*
C3	0.36041 (18)	0.4398 (2)	0.07702 (16)	0.0380 (7)
H3A	0.3738	0.4054	0.0201	0.046*
H3B	0.2916	0.4741	0.0763	0.046*
C4	0.43397 (18)	0.5417 (2)	0.09696 (15)	0.0323 (6)
C5	0.4179 (2)	0.6643 (2)	0.06884 (16)	0.0403 (7)
H5A	0.3602	0.6827	0.0351	0.048*
C6	0.4840 (2)	0.7580 (2)	0.08913 (17)	0.0420 (7)
H6A	0.4714	0.8404	0.0699	0.050*
C7	0.5688 (2)	0.7325 (2)	0.13751 (16)	0.0402 (7)
H7A	0.6150	0.7971	0.1510	0.048*
C8	0.58628 (19)	0.6125 (2)	0.16627 (16)	0.0349 (6)
H8A	0.6441	0.5951	0.2001	0.042*
C9	0.51916 (18)	0.5171 (2)	0.14575 (15)	0.0305 (6)
C10	0.54335 (17)	0.3891 (2)	0.18083 (16)	0.0322 (6)
H10A	0.6118	0.3653	0.1639	0.039*
H10B	0.5422	0.3920	0.2436	0.039*
C11	0.64579 (19)	0.0554 (2)	0.09105 (16)	0.0340 (6)
H11A	0.6250	0.0255	0.0368	0.041*
C12	0.73080 (19)	0.0266 (2)	0.13346 (17)	0.0384 (7)
H12A	0.7815	−0.0266	0.1124	0.046*
C13	0.65196 (18)	0.1497 (2)	0.21454 (16)	0.0331 (6)
H13A	0.6337	0.1999	0.2614	0.040*

Atomic displacement parameters (Ų)

	U^11	U^22	U^33	U^12	U^13	U^23
O1	0.0293 (10)	0.0374 (10)	0.0441 (11)	−0.0062 (8)	−0.0048 (9)	−0.0058 (9)
N1	0.0209 (11)	0.0286 (11)	0.0385 (13)	0.0003 (9)	−0.0068 (9)	−0.0016 (10)
N2	0.0274 (11)	0.0280 (11)	0.0308 (11)	0.0013 (9)	−0.0017 (9)	0.0006 (9)
N3	0.0323 (13)	0.0352 (12)	0.0509 (15)	0.0053 (10)	−0.0070 (11)	0.0022 (11)
C1	0.0231 (13)	0.0329 (14)	0.0316 (14)	−0.0002 (11)	0.0002 (11)	0.0025 (12)
C2	0.0229 (13)	0.0381 (15)	0.0461 (16)	0.0029 (11)	−0.0048 (12)	−0.0016 (13)
C3	0.0287 (14)	0.0454 (16)	0.0395 (15)	0.0065 (12)	−0.0088 (12)	−0.0047 (13)
C4	0.0339 (15)	0.0353 (14)	0.0277 (13)	0.0049 (12)	−0.0027 (12)	−0.0021 (12)
C5	0.0453 (17)	0.0435 (16)	0.0320 (15)	0.0101 (14)	−0.0047 (13)	0.0042 (13)
C6	0.0566 (19)	0.0327 (15)	0.0367 (16)	0.0032 (13)	0.0011 (14)	0.0057 (13)
C7	0.0501 (19)	0.0321 (14)	0.0385 (16)	−0.0032 (13)	0.0012 (14)	0.0002 (13)
C8	0.0362 (15)	0.0339 (14)	0.0345 (15)	−0.0019 (12)	−0.0013 (12)	−0.0009 (12)
C9	0.0330 (15)	0.0304 (13)	0.0280 (13)	0.0012 (11)	−0.0001 (12)	−0.0024 (11)
C10	0.0275 (14)	0.0270 (13)	0.0419 (15)	−0.0021 (11)	−0.0080 (12)	−0.0011 (12)
C11	0.0357 (15)	0.0306 (14)	0.0355 (14)	0.0030 (12)	0.0003 (12)	−0.0059 (12)
C12	0.0334 (16)	0.0332 (14)	0.0487 (17)	0.0069 (12)	0.0052 (13)	0.0015 (13)
C13	0.0321 (14)	0.0299 (13)	0.0371 (15)	0.0012 (12)	−0.0067 (12)	0.0014 (12)

Geometric parameters (Å, º)

O1—C1	1.218 (3)	C4—C5	1.406 (3)
N1—C1	1.344 (3)	C5—C6	1.374 (3)
N1—C10	1.462 (3)	C5—H5A	0.9500
N1—C2	1.467 (3)	C6—C7	1.383 (4)
N2—C13	1.365 (3)	C6—H6A	0.9500
N2—C11	1.383 (3)	C7—C8	1.385 (3)
N2—C1	1.431 (3)	C7—H7A	0.9500
N3—C13	1.308 (3)	C8—C9	1.396 (3)
N3—C12	1.384 (3)	C8—H8A	0.9500
C2—C3	1.511 (3)	C9—C10	1.516 (3)
C2—H2A	0.9900	C10—H10A	0.9900
C2—H2B	0.9900	C10—H10B	0.9900
C3—C4	1.501 (3)	C11—C12	1.345 (3)
C3—H3A	0.9900	C11—H11A	0.9500
C3—H3B	0.9900	C12—H12A	0.9500
C4—C9	1.388 (3)	C13—H13A	0.9500
C1—N1—C10	126.47 (18)	C5—C6—C7	120.1 (2)
C1—N1—C2	118.61 (19)	C5—C6—H6A	120.0
C10—N1—C2	114.72 (18)	C7—C6—H6A	120.0
C13—N2—C11	105.99 (19)	C6—C7—C8	119.8 (2)
C13—N2—C1	130.0 (2)	C6—C7—H7A	120.1
C11—N2—C1	123.2 (2)	C8—C7—H7A	120.1
C13—N3—C12	104.6 (2)	C7—C8—C9	120.2 (2)
O1—C1—N1	125.1 (2)	C7—C8—H8A	119.9
O1—C1—N2	118.7 (2)	C9—C8—H8A	119.9
N1—C1—N2	116.1 (2)	C4—C9—C8	120.4 (2)
N1—C2—C3	110.1 (2)	C4—C9—C10	122.8 (2)
N1—C2—H2A	109.6	C8—C9—C10	116.7 (2)
C3—C2—H2A	109.6	N1—C10—C9	112.19 (18)
N1—C2—H2B	109.6	N1—C10—H10A	109.2
C3—C2—H2B	109.6	C9—C10—H10A	109.2
H2A—C2—H2B	108.1	N1—C10—H10B	109.2
C4—C3—C2	110.39 (19)	C9—C10—H10B	109.2
C4—C3—H3A	109.6	H10A—C10—H10B	107.9
C2—C3—H3A	109.6	C12—C11—N2	106.0 (2)
C4—C3—H3B	109.6	C12—C11—H11A	127.0
C2—C3—H3B	109.6	N2—C11—H11A	127.0
H3A—C3—H3B	108.1	C11—C12—N3	111.0 (2)
C9—C4—C5	118.2 (2)	C11—C12—H12A	124.5
C9—C4—C3	120.4 (2)	N3—C12—H12A	124.5
C5—C4—C3	121.4 (2)	N3—C13—N2	112.4 (2)
C6—C5—C4	121.3 (2)	N3—C13—H13A	123.8
C6—C5—H5A	119.4	N2—C13—H13A	123.8
C4—C5—H5A	119.4

Hydrogen-bond geometry (Å, º)

D—H···A	D—H	H···A	D···A	D—H···A
C11—H11A···O1^i	0.95	2.56	3.480 (3)	164
C12—H12A···O1^ii	0.95	2.31	3.227 (3)	161

Symmetry codes: (i) −x+1, −y, −z; (ii) x+1/2, −y, z.