Reactions of 2,5-Dihydrothiophen and S-substituted derivatives with bases. Preparations of 1-(Alkylthio)buta-1,3-dienes and the corresponding sulfoxides and sulfones

Under certain conditions the anions from 2,5-dihydrothiophen 1-oxide and 2,5-dihydrothiophen 1,l-dioxide undergo ring-opening reactions and the resulting buta-1,3-dienylsulfenate and buta-1,3- dienylsulfinate ions respectively may be alkylated. The anion from 2,5-dihydrothiophen also rearranges to the buta-1,3-dienylthiolate ion which may be alkylated, but the overall reaction is incomplete and pure products cannot be isolated; instead 1-(alkylthio)buta-1,3-dienes may conveniently be prepared by base-catalysed ring-opening reactions of 1-alkyl-2,5-dihydrothiophenium salts. The 1-(alkylthio), 1-(alkylsulfinyl)- and 1-(alkylsulfonyl)buta-1,3-dienes isolated from the above reactions are very unstable, and rapidly polymerize on standing at ambient temperatures.