Studies on the chemical constituents of rutaceous plants. LV. The development of a versatile method for the synthesis of antitumor-active benzo(c)phenanthridine alkaloids. 5. A new method for quaternization of the benzo(c)phenanthridine nucleus.

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Abstract
A versatile method of synthesis of the quaternary benzo[c]phenanthridine alkaloid (1), having a tertiary benzo[c]phenanthridine skeleton, from the norbase (3) is described. Treatment of (3) with sodium borohydride in formic or in acetic acid gave the N-methyl-(5) or the N-ethyl-(7) dihydrobase, respectively, in good yield; (5) could also be prepared by treatment of (3) with sodium borohydride and dimethyl sulfate in hexamethylphosphoric triamide. The dihydrobases (5 and 7) were readily convertible to the corresponding quaternary benzo[c]phenanthridine alkaloids by oxidation with Jones reagent or with 2,3-dichloro-5,6-dicyano-1,4-benzoquinone (DDQ) in good yields. The air-oxidation of the carbanions derived from the .psi.-cyanides of the quaternary bases (1) gave the corresponding oxybases in excellent yields.