CONFORMATION AND FACIAL SELECTIVITIES OF CHIRAL 6-MEMBERED 1,3-DIHETEROCYCLES INVOLVING AN ENONE FUNCTION

Ground-state as well as excited-state reactions of chiral 1,3-dioxin-4 -ones and related compounds which involve an enone function in their r ing are reviewed with emphasis of the facial selectivity. Sofa conform ation of the ring systems and pyramidalization of the enone portions i n these heterocycles so far been proposed as the origins of the facial selectivity are summarized and the discrepancies between facial selec tivities verified by experimental results and the predicted selectivit ies from either the conformation or the pyramidalization are pointed o ut. The reactions of chiral 1,3-dioxane-4,6-diones, 1,3-oxazine-4,6-di ones and their 5-benzylidene derivatives are also surveyed. Finally, t he present authors' opinion which accounts for all of the reported rea ctions having facial selectivities is proposed. This review also inclu des the present authors' opinion for the origin of these conformation and pyramidalization.