a,a-Disubstituted Allyl Sulfones: An approach to the synthesis of vinyl-branched pheromone analogues

The two-step alkylation of phenyl prop-2-enyl sulfone (1) with protected -bromoalkanols and 1-iodoalkanes (3; see Scheme 1) followed by a Pd-catalyzed desulfonylation with LiBH4 affords a 96:4 mixture of vinylbranched, protected alcohols and corresponding ethylidene-branched isomers (see Scheme 2; 4 and 5, respectively). By utilizing the large difference in reactivity of mono- and trisubstituted CC bonds towards singlet oxygen, the ethylidene derivatives are easily removed from the mixture by photo-oxygenation. The vinyl-branched compounds are inert to this reaction and can be conveniently isolated in highly pure form (99.5%) and ca. 45% overall yield.