213. Synthesis of Triafulvene-Precursors from Trisubstituted Cyclopropanes

Article abstract of DOI:10.1002/hlca.19880710820

Trisubstituted cyclopropanes 5a-f are prepared by carbene addition to the appropriate olefins.While 5a (Y = OAc) and 5c (Y = Cl) rearrange in the presence of BuLi, 5d (Y = SPh) is stable enough to allow the envisaged sequence for triafulvene (Scheme 2); halogen-Li exchange, followed by methylation of 6d, gives 7d in a 93percent yield; after base-induced elimination of HBr from 7d, the key precursor 1-methylene-2-(phenylthio)cyclopropane (9, 70percent yield) is isolated.Compound 9 is transformed into the corresponding sulfoxide 10 (83percent), sulfone 11 (80percent), and sulfonium fluoroborate 12 (95percent yield) by subsequent oxidation and methylation, respectively.Some 1H NMR results of cyclopropanes 5a-f and 7d as well as of methylidene-cyclopropanes 9-11 are discussed.