Alkatrienyl sulfoxides and sulfones. Part I. 3-methyl-1,2,4-pentatrienyl phenyl sulfoxide-synthesis and electrophile-induced cyclization reactions

Article abstract of DOI:10.1080/10426500214293

A method for the synthesis of the 3-methyl-1,2,4-pentatrienyl phenyl sulfoxide 3 by [2,3]-sigmatropic rearrangement of the 3-methyl-1-penten-4-yn-3-yl benzenesulfenate 2, formed in the reaction of the 3-methyl-1-pentene-4-yn-2-ol 1 with phenylsulfenyl chloride has been created. Possibilities and restrictions of the five-membered heterocyclization in electrophile-induced reactions leading to the synthesis of the 5H-1,2-oxathiol-2-ium salts 5, 7, and 8 have been explored. Chlorination of the sulfoxide 2 proceeded with formation of the (E)-2-chloro-3-methylene-1,4-pentadienyl phenyl sulfoxide 4, while the bromination afforded the 4-bromo-5H-1,2-oxathiol-2-ium bromide 5, which after reflux in 1,2-dichloroethane eliminated hydrogen bromide and was transformed into the (E)-2-bromo-3-methylene-1,4-pentadienyl phenyl sulfoxide 6.