Research Projects

Carbene intermediates play a pivotal role in organic synthesis, participating in key transformations such as the Wolff rearrangement, C–X bond insertion, ylide formation, [2+1] cycloaddition, and various other cycloaddition reactions. While most carbenes are inherently electron-deficient species, certain carbenes bearing an adjacent electron-donating atom—such as in N-heterocyclic carbenes (NHCs)—exhibit nucleophilic character. This unique reactivity of latter enables their use as NHC-organocatalysts.2 Recent advancements in metal-catalyzed and photochemical carbene transfer reactions, using stable carbene precursors such as diazo compounds and N-tosylhydrazones, have significantly broadened the scope of carbene chemistry. Moreover, the development of enantioselective reactions enabled by NHCs has further expanded their synthetic utility. While individual reactions involving carbenes—either as reactive intermediates or as catalysts—are widely employed in carrying out interesting and unusual organic transformations as well as in the synthesis of pharmaceuticals, natural products, and functional materials, the strategic combination of multiple carbene species in a single transformation remains underexplored. Notably, only a few studies have reported the use of two distinct carbene intermediates, typically involving a metal- or light-generated carbene trapped by an NHC-derived intermediate. To the best of our knowledge, a sequential relay process involving three discrete carbene species has not yet been described. In this context, we propose a unique strategy that entails the generation of two different intermediates from distinct carbene precursors. One of the such carbene-generated intermediate is proposed to be intercepted under NHC catalysis to initiate a stereoselective transformation by engaging the second carbene generated intermediate in a cascade process. This sequential carbene relay approach aims to construct complex fused-ring systems with high efficiency and selectivity. Such a one-pot multistep carbene relay represents an innovative synthetic platform, enabling the sequential transfer and harnessing of carbene intermediates to access diverse and architecturally intricate molecular frameworks.