(Z)-1,3,4a-Trimethyl-5,5-diphenyl-6-oxa-1,3-diaza­bicyclo­[4.2.0]octane-2,4-dione

Zhi-Cai Lin; Jing-Bo Shi; Wen-Jian Tang; Jun Li

doi:10.1107/S1600536808006557

. 2008 Apr 4;64(Pt 5):o796. doi: 10.1107/S1600536808006557

(Z)-1,3,4a-Trimethyl-5,5-diphenyl-6-oxa-1,3-diazabicyclo[4.2.0]octane-2,4-dione

Zhi-Cai Lin ^a, Jing-Bo Shi ^a, Wen-Jian Tang ^a,^*, Jun Li ^a

PMCID: PMC2961230 PMID: 21202288

Abstract

The title compound, C₂₀H₂₀N₂O₃, is a head-to-tail oxetane, one of the regioisomers obtained by the the Paternó–Büchi reaction of 1,3-dimethylthymine with benzophenone. The oxetane ring is folded, the dihedral angle between the C—O—C and C—C—C planes being 14.4 (2)°. The dihedral angle between the two phenyl rings is 64.3 (2)°. The pyrimidine ring adopts a boat conformation. The crystal structure involves weak C—H⋯O hydrogen bonds.

Related literature

For related literature, see: Hei et al. (2005 ▶); Prakash et al. (1997 ▶).

Experimental

Crystal data

C₂₀H₂₀N₂O₃
M _r = 336.38
Monoclinic,
a = 8.1341 (7) Å
b = 9.1004 (13) Å
c = 23.485 (2) Å
β = 97.334 (2)°
V = 1724.2 (3) Å³
Z = 4
Mo Kα radiation
μ = 0.09 mm⁻¹
T = 298 (2) K
0.45 × 0.41 × 0.18 mm

Data collection

Bruker SMART diffractometer
Absorption correction: multi-scan (SADABS; Sheldrick, 1996 ▶) T _min = 0.962, T _max = 0.984
8774 measured reflections
3039 independent reflections
1818 reflections with I > 2σ(I)
R _int = 0.036

Refinement

R[F ² > 2σ(F ²)] = 0.044
wR(F ²) = 0.117
S = 1.01
3039 reflections
226 parameters
H-atom parameters constrained
Δρ_max = 0.20 e Å⁻³
Δρ_min = −0.18 e Å⁻³

Data collection: SMART (Siemens, 1996 ▶); cell refinement: SAINT (Siemens, 1996 ▶); data reduction: SAINT; program(s) used to solve structure: SHELXS97 (Sheldrick, 2008 ▶); program(s) used to refine structure: SHELXL97 (Sheldrick, 2008 ▶); molecular graphics: SHELXTL (Sheldrick, 2008 ▶); software used to prepare material for publication: SHELXTL.

Supplementary Material

Crystal structure: contains datablocks I, global. DOI: 10.1107/S1600536808006557/wn2239sup1.cif

e-64-0o796-sup1.cif^{(20.1KB, cif)}

Structure factors: contains datablocks I. DOI: 10.1107/S1600536808006557/wn2239Isup2.hkl

e-64-0o796-Isup2.hkl^{(149.2KB, hkl)}

Additional supplementary materials: crystallographic information; 3D view; checkCIF report

Table 1. Hydrogen-bond geometry (Å, °).

D—H⋯A	D—H	H⋯A	D⋯A	D—H⋯A
C3—H3⋯O2ⁱ	0.98	2.53	3.431 (3)	153
C7—H7⋯O1	0.93	2.37	2.745 (3)	104
C8—H8⋯O1ⁱⁱ	0.93	2.59	3.513 (3)	171
C13—H13⋯O1	0.93	2.41	2.752 (3)	101
C17—H17⋯O3	0.93	2.55	3.040 (3)	113
C20—H20B⋯O2	0.96	2.29	2.682 (4)	104

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Symmetry codes: (i) Inline graphic ; (ii) .

Acknowledgments

This work was supported by the Grants for Scientific Research of BSKY (grant No. XJ200712) from Anhui Medical University.

supplementary crystallographic information

Comment

A [2 + 2] photocycloaddition (Paternò-Büchi reaction) of the 5–6 double bond of 1,3-dimethylthymine (DMT) with the carbonyl of benzophenone generates two regioisomers, head-to-head and head-to-tail oxetanes (Fig. 1). We have observed the temperature dependence of the regioselectivity (Hei et al., 2005). The crystal structure of the head-to-head oxetane has already been published (Prakash et al., 1997). In the present study, an X-ray crystallographic analysis of the head-to-tail oxetane has been undertaken to establish its structure and configuration.

The structure is similar to that observed in the head-to-head oxetane (Prakash et al., 1997). The bond lengths and angles in the title compound are in good agreement with expected values. The oxetane ring is folded and the dihedral angle between the C1—O1—C3 and C1—C2—C3 planes is 14.4 (2)° (Fig. 2). The dihedral angle between the two phenyl rings is 64.3 (2)° and the pyrimidine ring adopts a boat conformation. The crystal structure involves weak C—H···O hydrogen bonds.

Experimental

The title compound was prepared by first dissolving DMT (0.77 g, 5.0 mmol) and benzophenone (1.82 g, 10.0 mmol) in CH₃CN (100 ml). The resulting solution was placed in a photochemical apparatus (Pyrex), purged with nitrogen, degassed for 30 min, and irradiated with a 300 W mercury high-pressure lamp for 10 h. The solvent was then rotary evaporated and the oxetane was purified by silica gel chromatography using a 4:1 petroleum ether/ethyl acetate solvent mixture. The fractions containing the h-t oxetane were combined, and the solvent removed by rotary evaporation. The purified oxetane was subsequently crystallized by dissolving the residue in 10 ml of ethyl acetate and adding n-hexane to the solution until it turned cloudy. Upon standing at room temperature, a colorless block appeared and was separated from the solvent by decanting.