Synthesis and Reactivity of α-Haloglycine Esters: Hyperconjugation in Action.

European J Org Chem

Department of Chemistry and Biochemistry, Florida Atlantic University, Physical Science Building, 777 Glades Road, Boca Raton, FL, 33431, United States.

Published: October 2019


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Article Abstract

A general and efficient synthesis of α-haloglycine esters from commercially available feedstock chemicals, in a single step, is reported. The reactivity of these α-haloglycine esters with various nucleophiles was studied as surrogates of α-iminoesters upon activation with hydrogen-bond donor catalysts. DFT calculations on the α-haloglycine structures (X = F, Cl, Br) accompanied by an X-ray characterization of the α-bromoglycine ester support the existence of a "generalized" anomeric effect created by hyperconjugation. This peculiar hyperconjugative effect is proposed to be responsible for the enhanced halogen nucleofugality leading to a facile halogen abstraction by hydrogen-bond donor catalysts. This reactivity was exploited with thiourea catalysts on several catalytic transformations (aza-Friedel-Crafts and Mannich reactions) for the synthesis of several types of non-proteinogenic α-amino esters.

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http://www.ncbi.nlm.nih.gov/pmc/articles/PMC7189931PMC
http://dx.doi.org/10.1002/ejoc.201901033DOI Listing

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