Conversion of 2,3‐Dihydrobenzo[b][1,4]dioxine‐2‐carboxamides to 3‐Oxoquinolin‐2(1H)‐ones via Ring‐Opening and Formal 6‐endo‐trig Cyclization‐Involved Heck Reactions

Abstract

We report the conversion of 2,3‐dihydrobenzo[b][1,4]dioxine‐2‐carboxamides, (derived from 2,3‐dihydrobenzo[b][1,4]dioxine‐2‐carboxylic acid and 2‐haloanilines) to 3‐oxoquinolin‐2(1H)‐one motifs using catalytic amounts of Pd(OAc)2, PPh3, BINOL and Cs2CO3 (1.5 equiv). This conversion occurred via the less common formal 6‐endo‐trig cyclization and chelation‐controlled β‐arylation (Heck‐type reaction) pathways. Initially, a base‐mediated ring‐opening of the 2,3‐dihydrobenzo[b][1,4]dioxine moiety generates an acrylamide intermediate in situ, which then undergoes a formal 6‐endo‐trig cyclization‐involved Heck‐type reaction to afford 3‐oxoquinolin‐2(1H)‐one motif. The proposed acrylamide intermediate was isolated, characterized by the X‐ray structure analysis and then, it was also treated under the experimental conditions, which afforded the expected 3‐oxoquinolin‐2(1H)‐one; thus, providing a strong support for the proposed mechanism. Various 3‐oxoquinolin‐2(1H)‐one motifs were synthesized in moderate to good yields. Representative 3‐oxoquinolin‐2(1H)‐one motifs were characterized by X‐ray analysis.