First reactions of vinylindoles with diethyl mesoxalate, nitrosobenzene, and chlorosulfonyl isocyanate: New functionalized and [b]annellated indoles

Abstract Diethyl mesoxalate reacts with 2- and 3-vinylindoles via electrophilic substitution to give new, functionalized and annellated indoles in high regioselectivities. Regio-controlled dimerization processes occur in the reactions of the vinylindoles 5a and 8a . Nitrosobenze reacts with 2- and 3-vinylindoles in a multi-stage sequence including regiospecific tandem hetero-Diels-alder reactions to give the new, 2,3-difunctionalized indoles 11 and 12 which are conformationally stabilized by proton chelation. The heterocumulene chlorosulfonyl isocyanate reacts as a simple electrophile (like diethyl mesoxalate) with 2-vinylindole 5b to give the indole-3-carboxamide 14 . In addition, analogous reactions of N -methylindole were also studied and, in most cases, gave comparable reactivity patterns.