A photo-driven traceless group directed electron-donor-acceptor (EDA) complex initiated radical coupling/dehydrogenation tandem reaction: access to 1-allyl/benzyl-3,4-dihydroisoquinoline

A metal-free and mild one pot protocol for traceless group directed and electron-donor-acceptor (EDA) complex initiated radical coupling/dehydrogenation of arylazo-protected tetrahydroisoquinolines with benzyl/allyl halides is reported. The reaction was carried out using the triazene group as a traceless directing group to form an EDA complex with benzyl/allyl bromide. The radical coupling/dehydrogenation tandem reaction was initiated by the EDA complex under purple light irradiation, and finally a series of novel 1-benzyl/allyl-3,4-dihydroisoquinoline compounds were obtained. This environmentally friendly reaction features advantages of transition-metal-, photocatalyst- and oxidant-free conditions and larger scale synthesis and provides the key intermediate for tetracyclic alkaloid (S)-xylopinine and papaverine synthesis. A metal-free and mild one pot protocol for the traceless group directed and electron-donor-acceptor (EDA) complex initiated radical coupling/dehydrogenation of arylazo-protected tetrahydroisoquinolines with benzyl/allyl bromide is reported.