Chiral space group photochemistry

Irradiation of a benzene solution of 5-phenyl Af-benzoylformyl-A-p-tolylthiocar-bamate 48a (Scheme 23) gave 5-phenyl-5-phenylthio-3-p-tolyloxazolidine-2,4-dione 49a in 61% yield accompanied by oxazolidine-2,4-dione dimer (15%), p-tolyl isocyanate (22%), and diphenyl disulfide [29]. Photolysis of 48a in the solid state gave oxazolidine-2,4-dione 49a in 96% yield. For the N-methyl derivative, 48b, compared to the solution photochemistry in which only 8% of oxazolidinedi-one 49b was obtained with a complex mixture, radical cyclization proceeds selectively to give oxazolidinedione in 75% yield in the solid state. Whereas N-p-tolyl and A-methyl derivatives, 48a and 48b, formed achiral crystals, the N-benzyl derivative 48c crystallized in chiral space group P2. Photolysis of the chiral... 

Unfortunately, nature is unreliable when it comes to providing chiral space groups for achiral molecules, and the great majority of achiral substances crystallize in centric or otherwise symmetric packing arrangements [6]. The question thus became not whether the chiral crystalline state would serve as a useful medium for asymmetric synthesis—this had already been demonstrated—but how a chiral space group could be guaranteed for the achiral compound whose photochemistry one wished to study. 

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