Stereospecific diaza-Cope rearrangement as an efficient tool for the synthesis of DPEDA pyridine analogs and related C2-symmetric organocatalysts

Abstract

A simple and efficient synthesis of enantiomerically pure (1S,2S)-1,2-di(pyridin-2-yl)- and (1R,2R)-1,2-di(pyridin-4-yl)-ethane-1,2-diamines from commercial picolinaldehyde or isonicotinaldehyde and 2,2′-((1S,2S)-1,2-diaminoethane-1,2-diyl)diphenol (HPEN) via a stereospecific diaza-Cope rearrangement has been developed. Diamine (R,R)-2b was readily converted to novel diastereomeric ionic group-supported bis-prolinamides (R,S)-1b and (R,R)-1b which appeared to be efficient organocatalysts of asymmetric cross-aldol reactions in aldehyde/aldehyde, ketone/ketone or ketone/aldehyde reagent systems under neat conditions to afford corresponding aldols in high yields and with up to 99% ee. Furthermore, catalyst (R,S)-1b could be reused over 15 times in the same or similar catalytic reactions exhibiting close to original activity and a high level of stereoinduction.