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.

Homologation of isocyanates with lithium carbenoids: A straightforward access to α-halomethyl- and α,α-dihalomethylamides [Homologation of Isocyanates with Lithium Carbenoids: A Straightforward Access to alpha-Halomethyl- and alpha,alpha-Dihalomethylamides] / V. Pace, L. Castoldi, A.D. Mamuye, W. Holzer. - In: SYNTHESIS. - ISSN 0039-7881. - 46:21(2014 Nov), pp. ss2014-z0416-fa.2897-ss2014-z0416-fa.2909. [10.1055/s-0034-1379209]

Homologation of isocyanates with lithium carbenoids: A straightforward access to α-halomethyl- and α,α-dihalomethylamides [Homologation of Isocyanates with Lithium Carbenoids: A Straightforward Access to alpha-Halomethyl- and alpha,alpha-Dihalomethylamides]

L. Castoldi
Secondo
;
2014

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.
amides; carbenoids; halides; lithiation; nucleophilic addition
Settore CHIM/06 - Chimica Organica
6-ott-2014
Article (author)
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Utilizza questo identificativo per citare o creare un link a questo documento: https://hdl.handle.net/2434/890698
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