On-Water Vinylogous Mukaiyama-Michael Addition of Heterocyclic 2-Silyloxydienes to 1,2-Diaza-1,3-dienes: One-Pot Three-Step Entry to Functionality-Rich Pyrroles

Densely substituted pyrrole-carboxylates have been prepared in good yields in a highly practical one-pot three-step procedure. The key reaction of this process, which involves an uninterrupted sequence of reactions on-water, is a diastereoselective vinylogous Mukaiyama–Michael addition reaction (VMMcR) of heterocyclic 2-silyloxydienes to 1,2-diaza-1,3-dienes mediated by water itself. Subsequent in situ addition of catalytic aqueous sodium carbonate promotes an intramolecular aza-Michael addition with final ring-opening and aromatization. The superior use of water in the VMMcR as both reaction medium and promoter vis-à-vis deployment of conventional Lewis acids in organic solvents is highlighted, which provides the best results in terms of reaction rate, efficiency, stereoselectivity, and overall practicality.