SOLID-STATE DI-PI-METHANE TYPE PHOTOREARRANGEMENTS AND A CASE OF EFFICIENT SPONTANEOUS CHIRAL CRYSTALLIZATION

Photochemical solid state di-pi-methane type photorearrangements of a seemingly homo-chirally crystallized achiral alpha,delta-dienone (1) g ive preparative quantities of two optically active di-pi-methane photo products (2 and 3) of synthetic value. Considerable changes in product selectivity are observed for runs in homogeneous solution vs. the sol id state and form the basis of mechanistic pathway interpretations and propositions. Notably, the starting dienone 1 adopts chiral packing ( space group P2(1)2(1)2(1)) With some relatively short intermolecular d istances. The photorearrangements proceed so that the products are obt ained in respective enantiomeric excesses of less than or equal to 96 % (2) and less than or equal to 34 % (3). Reaction selectivity changes have been followed as a function of conversion for both irradiations of crystal batches and single crystals. Extensive structural modificat ions of 1 (4-7) have been made for a study of the crystallization and reaction properties of this class of compounds.