(1S*,4aR*,5S*,6S*,8aR*)-3-Benzyl-1-methyl-5,6-diphenyl-3,4,4a,5,6,8a-hexahydro-1H-2,3-benzoxazin-4-one

In the title compound, C28H27NO2, the oxazinone ring adopts a twist-boat conformation and the cyclohexene ring has a twisted envelope conformation. The crystal structure is stabilized by weak non-classical intermolecular C—H⋯O hydrogen bonds.

In the title compound, C 28 H 27 NO 2 , the oxazinone ring adopts a twist-boat conformation and the cyclohexene ring has a twisted envelope conformation. The crystal structure is stabilized by weak non-classical intermolecular C-HÁ Á ÁO hydrogen bonds.
In the crystal structure of the title compound, there are one oxazinone ring and one cyclohexene ring. The oxazinone ring C1-C2/C7-C8/O2-N1 adopts a twist-boat conformation, whereas the cyclohexene ring C2-C7 has a twisted envelope conformation. Bond length of C3-C4 is larger than normal C-C single bond because of the hindrance between two phenyl rings at C3 and C4. The crystal packing (Fig. 2) is stabilized by weak non-classical intermolecular C-H···O hydrogen bonds; the first between an H atom of the cyclohexene ring and the oxygen of the CO unit, with a C6-H6···O1 i , the second between an H atom of the ringjunction carbon and the oxygen of the CO unit, with a C7-H7···O1 ii , respectively (Table 1).

Experimental
To a 10 ml pressurized process vial was added racemic (3E,5E)-6-phenylhexa-3,5-dien-2-yl N-benzyl-cinnamoylhydroxamate (93.0 mg, 0.23 mmol) and MeCN (5 ml). The loaded vial was then sealed with a cap containing a silicon septum, and put into the microwave cavity and heated at 453 K for 30 min (the holding time) with the temperature measured by an IR sensor. After cooling to room temperature, the reaction mixture was concentrated under reduced pressure and the residue was then purified by colum chromatography (silica gel, 5% EtOAc in petroleum ether) to give the title compound in 10% yield (9.0 mg) as a white solid, and another two stereomers (in 29% and 49% yield, respectively). For the title compound, m.p. 464-466 K (EtOAc-hexane). Single crystals suitable for X-ray diffraction of the title compound were grown in the mixed solvent of ethyl acetate and hexane.

Refinement
The H atoms were placed in calculated positions with C-H = 0.93-0.98 Å, and included in the refinement in riding model, with U iso (H) = 1.2U eq (carrier atom).
supplementary materials sup-2 Figures Fig. 1. The molecular structure of the title compound with the atom numbering scheme. Displacement ellipsoids are drawn at 40% probability level. H atoms are presented as a small spheres of arbitrary radius.