Phase-Transfer-Catalyzed Asymmetric Acylimidazole Alkylation

Document Type

Article

Journal/Book Title

Organic Letters

Publication Date

2007

Publisher

American Chemical Society

Volume

9

Issue

23

First Page

4865

Last Page

4868

Abstract

2-Acylimidazoles are alkylated under phase-transfer conditions with cinchonidinium catalysts at −40 °C with allyl and benzyl electrophiles in high yield with excellent enantioselectivity (79 to >99% ee). The acylimidazole substrates are made in three steps from bromoacetic acid via the N-acylmorpholine adduct. The catalyst is made in high purity allowing for S-product formation (6−20 h) under mild conditions, consistent with an ion-pair mechanism. The products are readily converted to useful ester products using methyltriflate and sodium methoxide, via a dimethylacylimidazolium intermediate without racemization. The process is efficient, direct, and amenable to other electrophiles and transformations that proceed through an enolate intermediate.

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