Seleno/Thio-functionalized ipso-Annulation of N-Propiolyl-2-arylbenzimidazole to Construct Azaspiro[5,5]undecatrienones

Abstract

Till date, the ipso-cyclization of propiolamides is limited to provide azaspiro­[4,5]­decatrienones. Herein, we present the first example of ipso-carbocyclization, leading to azaspiro­[5,5]-undecatrienones from N-propiolyl-2-arylbenzimidazoles, involving both the radical-based and electrophilic reactions. This report establishes an access to a wide range of chalcogenated (SCN/SCF3/SePh) benzimidazo-fused azaspiro­[5,5]­undecatrienones in good yields.

Iodo-Annulations of N-Benzyl-propiolamides Leading To Azaspiro[5.5]undecatrienones or Benzo[c]azepinones

“…Among these oxidants, CAN promoted the reaction to give the spirocycle 2a in 56% yield, while the others gave inferior yields (Table 1, entries 4-7). Screening of other solvents (dichloromethane, tetrahydrofuran and dichloroethane) revealed that dichloromethane was the best solvent, delivering the product 2a in 86% yield (Table 1, entries [8][9][10]. Reducing the amount of I 2 to 0.5 equivalents led to the formation of 2a in a lower yield (52%), while increasing the quantity of I 2 to three equivalents did not increase the yield (Table 1, entries 11 and 12).…”

“…7 Very recently, we developed a seleno/thio-functionalized ipso-annulation of N-propiolyl-2-arylbenzimidazoles. 8 In this context, we herein present CANmediated divergent iodo-annulations of N-benzyl-propiolamides, producing either azaspiro[5.5]undecatrienones or benzo [c]azepinones (Scheme 1d). Further, methods for con-…”