Two syntheses of 7,8-dichloro-1,2,3,4-tetrahydroisoquinoline-1-14C

Two complementary radiosynthetic routes to the potent PNMT inhibitor 7,8-dichloro-1,2,3,4-tetrahydroisoquinoline-1-14C(1) from 2,3-dichlorobenzaldehyde-formyl-14C(4) are described. In the Pomeranz-Fritsch sequence isoquinoline 6 was prepared from Schiff's base 5. Catalytic hydrogenation of 6 (H2/PtO2) furnished 1 in 28% radiochemical yield from 4. In the aluminum chloride fusion sequence, 4 was converted via amino alcohol 7 to chloro amine 8. Treatment of the latter with aluminum chloride/ammonium chloride (fusion, 190°C) yielded labeled 1 in 31% radiochemical yield from 4.