Mechanism of a Dually Catalyzed Enantioselective Oxa-Pictet-Spengler Reaction and the Development of a Stereodivergent Variant

Enantioselective oxa-Pictet-Spengler reactions of tryptophol with aldehydes proceed under weakly acidic conditions utilizing a combination of two catalysts, an indoline HCl salt and a bisthiourea compound. Mechanistic investigations revealed the roles of both catalysts and confirmed the involvement of oxocarbenium ion intermediates, ruling out alternative scenarios. A stereochemical model was derived from density functional theory calculations, which provided the basis for the development of a highly enantioselective stereodivergent variant with racemic tryptophol derivatives.

Automated summary

The enantioselective oxa-Pictet-Spengler reactions of tryptophol with aldehydes were successfully conducted under weakly acidic conditions using a combination of indoline HCl salt and bisthiourea compound as catalysts. Mechanistic investigations determined the roles of both catalysts and confirmed the involvement of oxocarbenium ion intermediates, ruling out alternative scenarios. A stereochemical model derived from density functional theory calculations provided the basis for the development of a highly enantioselective stereodivergent variant with racemic tryptophol derivatives.