M. Hoskovec et al., ALPHA,ALPHA-DISUBSTITUTED ALLYL SULFONES - AN APPROACH TO THE SYNTHESIS OF VINYL-BRANCHED PHEROMONE ANALOGS, Helvetica Chimica Acta, 77(5), 1994, pp. 1281-1287
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.