Triphenylphosphine-induced ring contraction of 1,2-dioxines.

Triphenylphosphine inserts into the peroxide bond of 1,2-dioxines, initiating ring contraction with loss of triphenylphosphine oxide. This process yields dihydrofuran oxides in 54-97% yield from oxirenyl[2,3-c][1,2]dioxines and dihydrofurans from 3,6-dihydro-1,2-dioxines with inversion of stereochemistry at either the 2 or 5 position in the furan product.