Unusual sulfur chemistry in the thermal reaction of sultene and thiophene endoperoxide sulfur donors with cyclic alkynes: reversible formation of a persistent thiirenium ion and trapping of a thiirene by [4 + 2] cycloaddition

Waldemar Adam; Sara G Bosio; Bettina Fröhling; Dirk Leusser; Dietmar Stalke

doi:10.1021/ja025934x

Unusual sulfur chemistry in the thermal reaction of sultene and thiophene endoperoxide sulfur donors with cyclic alkynes: reversible formation of a persistent thiirenium ion and trapping of a thiirene by [4 + 2] cycloaddition

J Am Chem Soc. 2002 Jul 17;124(28):8316-20. doi: 10.1021/ja025934x.

Authors

Waldemar Adam¹, Sara G Bosio, Bettina Fröhling, Dirk Leusser, Dietmar Stalke

Affiliation

¹ Institut für Organische Chemie, Am Hubland, Würzburg, Germany. adam@chemie.uni-wuerzburg.de

PMID: 12105912
DOI: 10.1021/ja025934x

Abstract

The highly reactive cyclooctyne 2b serves as sulfur acceptor for both sulfur donors, namely the sultene 1A and thiophene endoperoxide 1B to afford sulfur-transfer products. With the acid-activated sultene 1A, the persistent thiirenium ion 3Ab is formed, which has allowed the direct observation of the initial sulfur-transfer adduct. On treatment with base, the thiirenium ion 3Ab reverts quantitatively to the cyclooctyne and sultene, whereas in neutral media it rearranges to the diene 6Ab. The rearrangement to the diene 6Ab, as well as the formation of spirocyclic adduct 6Ac in the reaction with dithiocyclononyne 2c, is proposed to proceed through a carbene mechanism. In the reaction of the cyclooctyne 2b with thiophene endoperoxide 1B, a thiirene is formed through sulfur transfer by an intermediary oxathiirane derived from the thiophene endoperoxide; as final product, the episulfide (R*,R*,R*)-3Bb is produced diastereoselectively by immediate [4 + 2] cycloaddition of the thiirene with the heterodiene 4B.