Condensation of 3‐methylbenzoxazolinone with α,β‐unsaturated acids

The reaction between 3‐methylbenzoxazolinone and some unsaturated acids in PPA leads to mixtures of compounds, depending on the acid: 6‐crotonyl‐ (or cinnamoyl)‐3‐methylbenzoxazolinones, 2,3‐dihydro‐2,5‐(or 2,7)dioxo‐3‐methylcyclopenta[ f ]benzoxazoles and 6‐(3‐oxo‐indanyl)‐3‐methylbenzoxazolinones. The structure of the products was established by 13 C and 1 H nmr spectroscopy and (or) by independent synthesis. Possible mechanisms of the reaction are discussed; when competition is possible as in the last step of the cyclization, the benzene ring shows a higher reactivity than the aromatic nucleus of the benzoxazolinone; the contrary is observed when the benzene ring is p ‐chloro‐substituted.