(1,2-Diaminoethane-1,2-diyl)bis(N‑methylpyridinium) Salts as a Prospective Platform for Designing Recyclable Prolinamide-Based Organocatalysts

A new efficient and highly recyclable organocatalyst has been developed for asymmetric cross-aldol reactions under neat conditions in ketone–ketone, ketone–aldehyde, and aldehyde–aldehyde systems. The catalyst features two prolinamide fragments and a C 2-symmetrical (1,2-diaminoethane-1,2-diyl)­bis­(N-methylpyridinium) group. The catalyst retained high activity and excellent stereoselection over the operating period of more than 830 h (25 cycles). An ab initio theoretical investigation explained the absolute configuration of the products and different stereoinduction levels for designed diastereomeric organocatalysts.