ISOQUINOLINE FORMATION VIA IMINIUM IONS CYCLIZATION - A DIRECT APPROACH TO C-2' FUNCTIONALIZED 3-ARYLTETRAHYDROISOQUINOLINES

3-Aryltetrahydroisoquinoline derivatives can be efficiently prepared b y titanium tetrachloride promoted cyclization of N-methoxymethyl-N-12- diarylethylamines via iminium ions. In the case of primary amines, the l-aryl group prevents the alkylation of a second iminium ion, avoidin g dimerization. The mild reaction conditions are compatible with the p resence of acid sensitive groups; thus,the 2'-functionalized 3-aryltet rahydroisoquinoline 6a could be prepared in high yield without desilyl ation. Therefore, this is a good alternative to the protic acid cataly zed Pictet-Spengler methodology, wich gives low yields of desilylated- 3-aryltetrahydroisoquinolines 4 when applied to the 2'-functionalized amine 3a.