Allene formation by gold catalyzed cross-coupling of masked carbenes and vinylidenes
- University of California Riverside–Centre National de la Recherche Scientifique Joint Research Chemistry Laboratory (Unité Mixte Internationale 2957), Department of Chemistry, University of California, Riverside, CA 92521-0403
-
Edited by Jack Halpern, University of Chicago, Chicago, IL, and approved July 11, 2007 (received for review June 21, 2007)
Abstract
Addition of a sterically demanding cyclic (alkyl)(amino)carbene (CAAC) to AuCl(SMe2) followed by treatment with [Et3Si(Tol)]+[B(C6F5)4]− in toluene affords the isolable [(CAAC)Au(η2-toluene)]+[B(C6F5)4]− complex. This cationic Au(I) complex efficiently mediates the catalytic coupling of enamines and terminal alkynes to yield allenes and not propargyl amines as observed with other catalysts. Mono-, di-, and tri-substituted enamines can be used, as well as aryl-, alkyl-, and trimethylsilyl-substituted terminal alkynes. The reaction tolerates sterically hindered substrates and is diastereoselective. This general catalytic protocol directly couples two unsaturated carbon centers to form the three-carbon allenic core. The reaction most probably proceeds through an unprecedented “carbene/vinylidene cross-coupling.”
Footnotes
- *To whom correspondence should be addressed. E-mail: gbertran{at}mail.ucr.edu
-
Author contributions: V.L. designed research; G.D.F. and S.K. performed research; B.D. contributed new reagents/analytic tools; and G.B. wrote the paper.
-
The authors declare no conflict of interest.
-
This article is a PNAS Direct Submission.
-
Data deposition: The atomic coordinates have been deposited in the Cambridge Structural Database, Cambridge Crystallographic Data Centre, Cambridge CB2 1EZ, United Kingdom (CSD reference nos. 651272–651275).
-
This article contains supporting information online at www.pnas.org/cgi/content/full/0705809104/DC1.
- Abbreviation:
- CAAC,
- cyclic (alkyl)(amino)carbene.
- © 2007 by The National Academy of Sciences of the USA
