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.

Chemoselective Reduction of Trichloromethyl Compounds to gem-Dichloromethyl Groups Following Appel's Reaction Protocol.

A simple and easy reduction of trichloroacetyl compounds following the modification of Appel's reaction protocol, using triphenylphosphine and methanol, afforded the corresponding dichloroacetyl compounds, with the exception of trichloroacetylmorpholine, in yields of 80-98% under very mild experimental conditions. Likewise, when trichloromethyl heterocyclic compounds contain another reactive functional group, the reaction is highly chemoselective giving the dichloromethyl derivative.