Acyclic Stereocontrol in Additions of Grignard Reagents to α-Alkoxyiminium Ions. A Stereoselective Approach to<i>threo</i>Amino Ethers

Abstract

The data in this paper suggest that reactions of Grignard reagents with dialkylaminofuranosides derived from pentoses proceed via α-alkoxyiminium ions and that these α-alkoxyiminium ions react quite stereoselectively. The rate of this reaction is dependent on the substituent at the 5-position of the pentose. A 5-deoxy analog is shown to react very slowly compared with a 5-O-methoxymethyl derivative. Importantly, the face selectivity of iminium ions with nucleophiles is shown to be opposite that expected and observed for reactions of aldehydes. A predictive mechanistic model is presented.