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, depending upon the molar concentrations of reagents, temperature and duration, isoquinolinylacetaldehydes (2), propanedials (3) or pyrroloisoquinolines (4). N-Acctylhomoveratryl amine (6) also afford under similar condition the dialdehyde 3b and pyrroloisoquinoline 4b. Vilsmeier-Haack (VH) reaction of the 1-methyl-8-nitroisoquinoline 1e under mild conditions gives the N-formyl derivative 8 and under vigorous conditions, pyrroloisoquinoline 4e. 1-Methylisoquinoline (9) and its 5,6,7,8-tetrahydro 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-Methylbenzoxazole even under forcing VH conditions yield only the dialdehydes and not the fused pyrroles.