Molecular iodine-mediated formal [2+1+1+1] cycloaddition access to pyrrolo[2,1-a]isoquinolines with DMSO as the methylene source

A molecular iodine-mediated formal [2+1+1+1] cycloaddition for the efficient synthesis of pyrrolo[2,1-a]isoquinolines from acetophenones, 1,2,3,4-tetrahydroisoquinoline (THIQ) and DMSO has been developed. Mechanistic studies revealed that DMSO served as the methylene source, and this novel protocol involves intermolecular cycloaddition of two in situ generated intermediates that enable efficient formation of one C-N bond and three C-C bonds via multiple sequential C-H functionalizations.