Ring-Opening Reactions of 2-Alkoxy-3,4-dihydropyrans with Thiols or Thiophenols

An electrophilic ring-opening reaction of 2-alkoxy-3,4-dihydropyran with a thiophenol or thiol is developed for the first time. The generated product contains not only a 1,3-dicarbonyl moiety but also a fragment of bis(alkylthio)methane. A possible mechanism is also proposed on the basis of postulating a ring-opening monotransthioacetalization product, which was prepared by using LiBr as catalyst as an intermediate.