Intramolecular cyclisation of 2-phenylethyl isocyanates

Abstract

Cyclisations of 2-phenylethyl isocyanate (2), (+)-1-methyl-2-phenylethyl isocyanate (3), and 2,2-diphenylethyl isocyanate (4) have been studied using polyphosphoric acid, aluminium chloride, boron trifluoride–diethyl ether, and triethyloxonium tetrafluoroborate. Depending on the reaction conditions, triethyloxonium tetrafluoroborate, for example, not only gave the expected isoquinolones (14)–(16) and other expected products, but in two cases, also gave the 2-N-(2-phenylethyl)formamidyl-3,4-dihydroisoquinolin-1 (2H)-ones (9) and (10). The isoquinolone (15) was alkylated with triethyloxonium tetrafluoroborate or methyl fluorosulphonate to give 1-ethoxy-(7) or 1-methoxy-3-methyl-3,4-dihydroisoquinoline (8), respectively.