Synthesis 2014; 46(21): 2897-2909
DOI: 10.1055/s-0034-1379209
feature article
© Georg Thieme Verlag Stuttgart · New York

Homologation of Isocyanates with Lithium Carbenoids: A Straightforward Access to α-Halomethyl- and α,α-Dihalomethylamides

Vittorio Pace*
a   Department of Pharmaceutical Chemistry – Division of Drug Synthesis, University of Vienna, Althanstrasse 14, 1090 Vienna, Austria   Fax: +43(1)42779556   Email: vittorio.pace@univie.ac.at
,
Laura Castoldi
a   Department of Pharmaceutical Chemistry – Division of Drug Synthesis, University of Vienna, Althanstrasse 14, 1090 Vienna, Austria   Fax: +43(1)42779556   Email: vittorio.pace@univie.ac.at
,
Ashenafi Damtew Mamuye
a   Department of Pharmaceutical Chemistry – Division of Drug Synthesis, University of Vienna, Althanstrasse 14, 1090 Vienna, Austria   Fax: +43(1)42779556   Email: vittorio.pace@univie.ac.at
b   Department of Chemistry and Pharmacy, University of Sassari, Via Vienna 2, 07110 Sassari, Italy
,
Wolfgang Holzer
a   Department of Pharmaceutical Chemistry – Division of Drug Synthesis, University of Vienna, Althanstrasse 14, 1090 Vienna, Austria   Fax: +43(1)42779556   Email: vittorio.pace@univie.ac.at
› Author Affiliations
Further Information

Publication History

Received: 02 July 2014

Accepted after revision: 03 September 2014

Publication Date:
06 October 2014 (online)


Abstract

Treatment of widely available isocyanates with monohalolithium and dihalolithium carbenoids provides a valuable protocol for the one-pot preparation of α-halo- and α,α-dihaloacetamide derivatives. While monohalolithium carbenoids can be prepared by a smooth lithium–halogen exchange, the preparation of the corresponding dihalo compounds proved to be highly dependent on the base used to realize the deprotonation, with lithium 2,2,6,6-tetramethylpiperidine emerging as optimal. The clear advantages of the procedure are: (a) broad scope of isocyanates that can be employed; (b) preservation of the optical purity when chiral materials are used; (c) divergent access to different haloamides by simply selecting the homologating agents. We also report an application of Charette’s imidoyl triflate activation of a secondary amide to the synthesis of an α-chloro ketone and 15N NMR data for selected compounds.

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