4826 J . Org. Chem., Vol. 43, No. 25, 1978
Cere et al.
Ring; Expansion by [2,3] Sigmatropic Shifts of Unstabilized Sulfonium Ylides. Synthesis of Eight- to Ten-Membered Thiacycloalk-4-enes V. Cere, C. Paolucci, S. Pollicino, E. Sandri, and A. Fava* Istituto di Chimica Organica, Universitci di Bologna, Viale Risorgirnento 4 , 40136 Bologna, I t ~ l ?
Received March 28, 1978
Vedejs' ring expansion procedure by a [2,3] sigmatropic shift of stabilized sulfonium ylidesl has been extended to nonstabilized ylides. The more favorable conditions (-90% yields) involve in situ ylide generation from sulfonium hexafluorophosphate salts (which are soluble in THF at low temperature) using t-BuOK as the base in the presence of t-BuOH. The geometry, E or 2 , of the cyclic homoallylic sulfide product could not be related to that, cis or trans, of the 1-alkyl-2-vinylcyclic sulfonium salt precursor, insofar as the latter was found to undergo rapid isomerization under the ring expansion conditions. A general synthesis is also reported of 2-~inylthiacycloalkanes, in particular the !six- and seven-membered compounds 8b and 8c. Vedejsl has recently reported the synthesis of thiacycloalk-4-enes by ring expansion of stabilized sulfonium ylides derived from 2-vinyl substituted cyclic sulfonium salts where n = 1 and 22 and R was an acid enhancing group such as
c a Scheme I a
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