Cycloadditions in syntheses. Part 47. 2-Monosubstituted 1,3-dioxin-4-ones: diastereofacial selectivity in pericyclic reactions and its explanation

Abstract

Photo[2 + 2]cycloaddition and Diels–Alder reactions of 2-monosubstituted 1,3-dioxin-4-ones have been examined for the first time. The observed stereoselectivities [the a-side (bottom side of sofa-type conformation of the dioxinone ring) preference for these pericyclic reactions and the b-side (top side of the sofa conformation) preferences for conjugated addition by lithium dimethylcuprate and catalytic hydrogenation] are the same with those reported previously for the dioxinones having a spirocyclic chiral auxiliary at the 2-position. A mechanism accounting for all the types of asymmetric reaction of these two types of chiral dioxinone is proposed.