Hyperconjugative effects in the stereoselective ring-opening reactions of oxetenoxides.

[reaction: see text] Unexpectedly, the pattern of the stereoselectivity in the ring-opening reactions of lithium oxetenoxides is not consistent with the bulkiness of substituents, and both the bulkier tert-butyl and silyl substituents favor inward rotation. With the aid of B3LYP calculations, the hyperconjugative interaction between the breaking C(1)-O sigma and its anti-periplanar Z-Me (Z = Si or C) sigma orbital is found to be responsible among the secondary orbital interactions of the substituents and the oxetene moiety.