Asymmetric Pictet-Spengler Reaction Using a-Methylbenzylamine as a Chiral Auxiliary Group

The Pictet-Spengler reaction of chiral N-(p-3-indoly1)ethyl-amethylbenzylamine with aldehydes in the presence of acids in refluxing benzene provided 1-substituted tetrahydro-pcarbolines (-72 % de).The tetrahydro-P-carbolines and tetrahydroisoquinolines which are structural feature present in many alkaloids are frequently synthesized by the well-known Pictet-Spengler reaction.l.2 Consequently, the method for canying out the Pictet-Spengler transformation in asymmetric manner is of important for synthetic organic chemistry.The reported procedures of asymmetric Pictet-Spengler reaction for tetrahydro-P-carboline synthesis involve the use of tryptophan alkyl ester3-5 or chiral aldehydes as enantiomerically pum starting materials.However, only a few examples which involve the use of subsequently removable chiral auxiliary groups in asymmetric Pictet-Spengler reaction have recently published : waldmann7 reported asymmetric Pictet-Spengler reaction of N-P-(3-indoly1)ethyl amino acid esters with achiral aldehydes, in which amino acid esters operated as the removable chiral auxiliary groups.