Abstract
Stereoelectronic control in the Pictet-Spengler condensation of Nb-alkylsubstituted tryptophan alkyl esters has been employed to promote 100% stereoselectivity in this process. The reaction of Nb-diphenylmethyl tryptophan isopropyl ester 8 with acetaldehyde in benzene at reflux yielded the trans-diastereomer 10d to the complete exclusion of the corresponding cis isomer. This trans stereospecificity was also observed for butyraldehyde and cyclohexylcarboxaldehyde.