Synthesis and stereochemistry of 4-tert-butyl-4-oxo-3,5,8-trioxa (3,5-dioxa-8-thia)-4-phosphabicyclo [5.1.0]octanes and related acetals

X-ray, 1H NMR and IR spectroscopy methods have been applied to a series of heterobicyclo[5.1.0]octanes. Endo epoxide and exo thiirane based on 2-tert-butyl-2-oxo-1,3,2-dioxaphosphepine exhibit chair form in a crystal state. Strong predominance of the chair conformation takes place in solution also as for similar bicyclic acetals produced from 2-tert-butyl-1,3-dioxacyclohept-5-ene. 3,5-Dioxa-8-thiabicyclo[5.1.0] octane bearing no a bulky substituent was found to exist as a mixture of stereoisomers in solution.