Thietanes are important intermediates in organic synthesis. They have been widely applied in the preparation
of sulfur-containing compounds via ring-opening and ring expansion. They produce thiols and thioether derivatives
via ring opening reactions and yield five- to eight-membered, even larger, heterocyclic compounds via
ring expansions. Ring opening and expansion reactions include electrophilic and nucleophilic, oxidative and reductive,
transition metals and acid-catalyzed, insertion, and photoirradiated processes. The ring opening and expansion
reactions generally show good regioselectivity. The electronic effect plays a crucial role in controlling the regioselectivity
in the ring opening and expansion reactions of unsymmetric thietanes invloving electropositive intermediates.
The regioselectivities in various ring opening reactions and expansions of unsymmetric thietanes are summarized
and discussed herein. Mechanisms on some of the important ring opening and expansion reactions of thietanes are introduced as well.
Keywords: Thietanes, heterocycle, four-membered ring, ring expansion, ring-opening, regioselectivity.
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