1.2- Dihydroisoquinolines, 1-allyl rearrangements

Methyl-1,2-dihydropapaverine (175, R = OMe) rearranges to the 2-methyl-3-(3,4-dimethoxybenzyl)-6,7-dimethoxy-3,4-dihydroisoquinolin-ium salt (176, R = OMe) under very mild conditions (treatment with 2% hydrochloric acid). A similar rearrangement of l-(3,4-methyl-enedioxybenzyl) - 2 - methyl - 6,7 - dimethoxyisoquinoline (175, R, R = —O—CHj—O—) affords 3-(3,4-methylenedioxybenzyl)-2-methyl-6,7-di-methoxy-3,4-dihydroisoquinolinium chloride (176, R, R = O—CHj—O—) (256). The reaction was shown to be an allylic rearrangement with internal return (275,275). 

AP831). Product 74 was obtained in only 10% yield, and a considerable part of the starting material (22a) was found to be resinified under the acidic conditions. The iminium salts 75 and 76 form in 23 and 49% yields, respectively. In both cases, disproportionation products could be isolated from 23a the compounds 77 and 78 in low yields and from 24a the compounds 79 and 80 in yields of about 15%. These findings demonstrate that the furo-(22a) and thienodihydropyridines (23a and 24a) under the rearrangement conditions behave similarly to the corresponding l-allyl-1,2-dihydroisoquinolines. 

Pseudocyanides. 6,7-Dimethoxy-2-methyl-l-allyl-l,2-dihydroisoquinoline dissolved in N H(5i, heated 0.5 hr. at 80° bath temp., cooled, made alkaline with NaHCOj, and treated with coned. NaCN-soln. pseudocyanide. Y 92%. F. rearrangements s. J. Knabe and H.-D. Holtje, Ardi. Pharm. 303, 404 (1970) Pharmazie 25, 313 (1970). 

When l-allyl-2-methyl-l,2-dihydroisoquinoline is heated with dilute mineral acid, a rearrangement occurs rapidly and in high yield to the 2-methyl-3-allyl-3,4-dihydroisoquinoline salt (14). This is an intramolecular suprafacial sigma-tropic [3,3] shift analogous to the Claisen and Cope rearrangements, with a transition state as denoted below. " ... 

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