14 15 the latter at reflux in toluene containing a trace of trifluoroacetic acid produced the fused pyrrole 15 in 78% yield. Thus, while the free carboxylic group in llb is unstable and undergoes decarboxylation to 12, the carboethoxy group in 14 remains intact en route to the pyrrole diester 15. This was verified by hydrolysis of 14 in aqueous ethanol containing dilute hydrochloric acid. Under these conditions, a mixture (1: l) of 12 and 15 was indeed ...
![ethyl 2,2,4,8-tetramethyl-5-oxa-1-azabicyclo[4.3.0]nona-6,8-diene-7-carboxylate Structure](https://image.chemsrc.com/caspic/114/51806-19-0.png)
![ethyl 2,2,4-trimethyl-5-oxa-1-azabicyclo[4.3.0]nona-6,8-diene-7-carboxylate Structure](https://image.chemsrc.com/caspic/142/34579-31-2.png)