Multicomponent construction of C3-unsubstituted iminocoumarins using CaC2 as a stable surrogate for gaseous acetylene: scope and mechanistic investigations

Abstract

A new route for the multicomponent construction of exclusively C3-unsubstituted iminocoumarin derivatives has been achieved in good yields using CaC₂ as a solid alkyne source along with o-hydroxyaryl aldehyde/ketone, and sulfonyl azide as precursors. The developed Cu(I)-catalyzed transformation proceeds efficiently at room temperature and is scalable up to the gram level. Experimental studies and DFT calculations were performed to assess the feasibility of critical steps in the reaction pathway. The reaction was found to proceed via a keteneimine intermediate, with dinuclear copper species playing a pivotal role in stabilizing the transition state over monomeric counterparts.