Synthesis and regioselective alkylation of 1,6- and 1,7-naphthyridines

A regioselective alkylation of naphthyridines 4a–d, through the action of ethylchloroformate and benzylstannane 5, afforded the benzyl substituted dihydronaphthyridines 3a–d. These key intermediates 3a–d were transformed into the desired targets 2a–d in seven steps.