Competitive Reactions of Alkylidenetriphenylphosphoranes and Methylsulfinyl Carbanion with 3-Methylenespiroundeca-1,4-diene

Article abstract of DOI:10.1021/jo00173a015

Treatment of 3-methylenespiro<5.5>undeca-1,4-diene (3) with methylenetriphenylphosphorane in Me2SO provides 3-ethylidenespiro<5.5>undeca-1,4-diene (4) as the major product in 33percent yield.The expected cyclopropane product dispiro<2.2.5.2>trideca-4,12-diene is obtained in only 1-2percent yield.Control experiments show that 4 arises from the reaction of the methylsulfinyl carbanion.Indeed, when 3 is treated with a Me2SO solution of the methylsulfinyl carbanion, multiple additions of the methylsulfinyl carbanion occur.The competition between the Wittig reagent and the methylsulfinyl carbanion in reaction with 3 can be shifted to favor the formation of cyclopropane products by increasing the nucleophilicity of the Wittig reagent by alkyl substitution at the carbanionic center.Thus, treatment of 3 with ethylidenetriphenylphophorane in Me2SO gives 4 and 1-methyldispiro<2.2.5.2>trideca-4,12-diene in yields of 28percent and 17percent, repectively, and reaction of 3 with isopropylidenetriphenylphosphorane in Me2SO gives 1,1-dimethyldispiro<2.2.5.2>trideca-4,12-diene in 64percent yield and less than a 1percent yield of 4.