ALPHA,ALPHA-DISUBSTITUTED ALLYL SULFONES - AN APPROACH TO THE SYNTHESIS OF VINYL-BRANCHED PHEROMONE ANALOGS

The two-step alkylation of phenyl prop-2-enyl sulfone (1) with protect ed omega-bromoalkanols and 1-iodoalkanes (--> 3; see Scheme 1) followe d by a Pd-catalyzed desulfonylation with LiBH4 affords a 96:4 mixture of vinyl-branched, protected alcohols and corresponding ethylidene-bra nched isomers (see Scheme 2;4 and 5, respectively). By utilizing the l arge difference in reactivity of mono- and trisubstituled C=C bonds to wards singlet oxygen, the ethylidene derivatives are easily removed fr om 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.