Studies on debenzylation and photolysis of 1-benzyl- and 1-(β-phenethyl)-1,2,3,4-tetrahydroisoquinolines

Govindachari, T. R. ; Nagarajan, K. ; Rajeswari, S. ; Suguna, H. ; Pai, B. R. (1977) Studies on debenzylation and photolysis of 1-benzyl- and 1-(β-phenethyl)-1,2,3,4-tetrahydroisoquinolines Helvetica Chimica Acta, 60 (7). pp. 2138-2150. ISSN 0018-019X

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Debenzylation of 1-(3-benzyloxybenzyl)-1,2,3,4-tetrahydroisoquinolines 1, 6, 7 with hydrochloric acid and ethanol gave the corresponding phenolic isoquinolines 2, 8, 9 and tetrahydroprotoberberines 4, 12, 13. Compounds 2, 8, 9 on photolysis also gave, besides the expected noraporphines 3, 10, 11, the tetrahydroprotoberberines 4, 12, 13 [1-4] (Schemes 1 and 2). 6-Benzyloxy-1-(5-benzyloxy-2-bromo-benzyl)-1,2,3,4-tetrahydroisoquinoline (27a) containing no methoxy or methylenedioxy groups either in ring A or C does not give protoberberine during debenzylation; but 28, the debenzylation product of 27a, on photolysis gives both the noraporphine 29 and the tetrahydroprotoberberine 30 (Scheme 6), proving that during debenzylation of 1-(3-benzyloxybenzyl)-1,2,3,4-tetrahydroisoquinolines containing additional methoxy or methylenedioxy groups, the necessary formaldehyde comes from the latter groups. During photolysis both the methoxy groups (methylenedioxy groups) and the C(3) atom of the tetrahydroisoquinoline moiety provide the formaldehyde. Veratrole under debenzylation and photolytic conditions and tetrahydroisoquinoline under the latter condition also give rise to formaldehyde (Schemes 8 and 10). The novel bromohomoprotoberberine 43 along with 42 was formed during debenzylation of the 1-phenethyl-1,2,3,4-tetrahydroisoquinoline 41. Photolysis of 42 yielded the novel nor-homoaporphine 44, in addition to 43; the latter was debrominated to give the homoberbine 45.

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