[3,3]-Sigmatropic rearrangement versus carbene formation in gold-catalyzed transformations of alkynyl aryl sulfoxides: mechanistic studies and expanded reaction scope.

Title[3,3]-Sigmatropic rearrangement versus carbene formation in gold-catalyzed transformations of alkynyl aryl sulfoxides: mechanistic studies and expanded reaction scope.
Publication TypeJournal Article
Year of Publication2013
AuthorsLu B, Li Y, Wang Y, Aue DH, Luo Y, Zhang L
JournalJournal of the American Chemical Society
Volume135
Issue23
Pagination8512-24
Date Published2013 Jun 12
Abstract

Gold-catalyzed intramolecular oxidation of terminal alkynes with an arenesulfinyl group as the tethered oxidant is a reaction of high impact in gold chemistry, as it introduced to the field the highly valued concept of gold carbene generation via alkyne oxidation. The proposed intermediacy of α-oxo gold carbenes in these reactions, however, has never been substantiated. Detailed experimental studies suggest that the involvement of such reactive intermediates in the formation of dihydrobenzothiepinones is highly unlikely. Instead, a [3,3]-sigmatropic rearrangement of the initial cyclization intermediate offers a reaction path that can readily explain the high reaction efficiency and the lack of sulfonium formation. With internal alkyne substrates, however, the generation of a gold carbene species becomes competitive with the [3,3]-sigmatropic rearrangement. This reactive intermediate, nevertheless, does not proceed to afford the Friedel-Crafts-type cyclization product. Extensive density functional theory studies support the mechanistic conclusion that the cyclized product is formed via an intramolecular [3,3]-sigmatropic rearrangement instead of the previously proposed Friedel-Crafts-type cyclization. With the new mechanistic insight, the product scope of this versatile formation of mid-sized sulfur-containing cycloalkenones has been expanded readily to various dihydrobenzothiocinones, a tetrahydrobenzocyclononenone, and even those without the entanglement of a fused benzene ring. Besides gold, Hg(OTf)2 can be an effective catalyst, thereby offering a cheap alternative for this intramolecular redox reaction.

DOI10.1080/19371918.2013.774675
Alternate JournalJ. Am. Chem. Soc.