Improved enamine-type addition of dehydroaporphine using microwave irradiation

Previous report demonstrated that 7-substituted aporphine, possessing interesting biological aspects, could be synthesized via an enamine-type addition of dehydroaporphine reacted with an electrophile, but it has the drawbacks of a long reaction time, low yield, and limitation to reactive electrophiles. Here we found that the reaction time and yield could greatly be improved under microwave irradiation in the presence of 4 equiv of sodium iodide for the synthesis of 7-benzyl dehydroglaucine. The application of this finding for treating dehydroglaucine with a variety of alkyl bromides also gave corresponding 7-substituted dehydroglaucines (2a-j) with yields of 14-89%. Other enamines such as 1,10-dimethoxydehydroaporphine (3a), 2,9-diacetyldehydroboldine (3b), and 7,8-dihydroberberine (5) were found to react with benzyl bromide under similar conditions as described above to give corresponding products (4a-b, 6) in satisfactory yields, indicating the versatility of this improved reaction condition.