Regioselective and stereoselective cleavage of cis-4-methyl-2-vinyl-l,3-dioxane by alkyllithiums.

The reaction of alkyllithiums with cis-4-methyl-2-vinyl-1,3-dioxane proceeds in virtually quantitative yield via a formal S(N)2' ring opening that proceeds in a regioselective manner to give preferential cleavage of the C(2)-O(l) bond remote from the 4-methyl substituent, affording the E-enol ether as the major stereoisomer. A two-step mechanism, involving addition of the alkyllithium followed by syn-elimination of lithium alkoxide, is suggested to account for the stereochemical outcome. Copyright 2002 Wiley Liss, Inc.