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Synthesis of Cyclic N-Tosyliminocarbonates by Lewis Acid Catalyzed Allylic Substitution of Trichloroacetimidates

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Abstract

Allylic trichloroacetimidates bearing a δ-N-tosylcarbamoyloxy group were prepared in two steps from the corresponding diols, and their Brønsted and Lewis acid catalyzed cyclization reactions were investigated. It was found that N-tosylcarbamates derived from secondary and tertiary alcohols bearing alkyl substituents undergo a chemoselective allylic alkylation to give N-tosyliminocarbonates in good isolated yields. In turn, aryl-substituted substrates tend to give oxazolines by abstraction of the carbamate functionality. The cyclization of N-tosylcarbamates derived from secondary alcohols preferentially give trans-iminocarbonates. However, the trans selectivity varied and depended on the substitution pattern, configuration of the substrate, and the catalyst. A high trans selectivity could be achieved from (E) substrates by using TMSOTf as the catalyst. The synthetic utility of iminocarbonates was demonstrated by transforming them into 1,2-diols and cyclic carbonates as well as into N-tosyloxazolidinones by a halide ion-induced rearrangement.

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