Ortho-Hydroxylative ipso-Cyclization of N-arylpropiolamide

Abstract

A facile protocol for the tunable synthesis of 10-hydroxy-1-azaspiro[4.5]deca-3,6,8-trien-2-ones and benzo[b]pyrrolo[2,1-c][1,4]oxazin-3-ones is described. A tunable synthesis has been realized by the use of ZnBr₂/oxone and tetra-n-butylammonium bromide (TBAB)/oxone. The reaction proceeds smoothly with high efficiency and a broad substrate scope. Mechanistic studies indicate that an N-protecting group-assisted ortho-trapping reaction is involved. In the transformation, the reaction undergoes α-addition, ipso-cyclization, and ortho-trapping of the resulting spirocyclic species.