p-Toluenesulfonic acid → 5,6-dihydro-3-methoxy-12-phenylnaphtho[1,2-b][1,8]naphthyridin-7(12H)-one

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Reaction Steps

For example, with 3,4-dihydro-6-methoxy-1-napthalenone as the ketone and methyl 2-phenylaminonicotinate as the arylaminonicotinate, the 1,3-diketone, 3,4-dihydro-6-methoxy-2-[[2-(phenylamino)-3-pyridinyl]carbonyl]-1(2H)-napthalenone, results from the process of Example 8. To cyclize, reflux 9 g of the diketone in 400 ml of toluene containing a catalytic amount of p-toluenesulfonic acid. Collect the evolved water in a Dean-Stark trap. Remove the heat after 21/2 hours and allow the mixture to stand overnight. Distill the toluene under vacuum on a steam bath and crystallize the residue from acetonitrile, to provide the product 5,6-dihydro-3-methoxy-12-phenylnaphtho[1,2-b][1,8]naphthyridin-7(12H)-one, m.p. 234°-237.5° C., after crystallization from CH3CN.

Provenance & Evidence