Unexpected cis selectivity in the Pictet-Spengler reaction

Whilst cis:trans selectivity of about 4:1 can be obtained from Pictet-Spengler reactions between tryptophan methyl esters and aldehydes using conditions of kinetic control, much higher cis selectivity (>95:5) can be obtained when both the tryptophan derivative and the aldehyde possess a Suitable pi-system: preliminary results oil the scope and limitations of this exceptional stereocontrol are presented in this Letter. (C) 2009 Elsevier Ltd. All rights reserved.