VILSMEIER-HAACK REACTION OF 1-METHYL-3, 4-DIHYDROISOQUINOLINES - FORMATION OF (3,4-DIHYDROISOQUINOLIN-1-YL)ACETALDEHYDES AND PYRROLO[2,1-A]ISOQUINOLINES AND AN ATTEMPTED SYNTHESIS OF AAPTAMINE

Treatment of dihydroisoquinolines (1a-d) with DMF-POCl3 yields, depend ing upon the molar concentrations of reagents, temperature and duratio n, isoquinolinylacetaldehydes (2), propanedials (3) or pyrroloisoquino lines (4). N-Acctylhomoveratryl amine (6) also afford under similar co ndition the dialdehyde 3b and pyrroloisoquinoline 4b. Vilsmeier-Haack (VH) reaction of the 1-methyl-8-nitroisoquinoline 1e under mild condit ions gives the N-formyl derivative 8 and under vigorous conditions, py rroloisoquinoline 4e. 1-Methylisoquinoline (9) and its 5,6,7,8-tetrahy dro derivative (10) remain unchanged under these conditions, whereas 1 -ethyl-3,4-dihydroisoquinoline (11) forms only the N-formyl derivative (12). 2-Methylquinoline, 2-methylbenzimidazole and 2-Methylbenzoxazol e even under forcing VH conditions yield only the dialdehydes and not the fused pyrroles.