Dihydrostrychninonic acid

Robinson 1 has pointed out that the formation of dihydrostrychninonic acid, C2iH2206N2, rectangular plates, m.p. 315°, [a] ° -)- 4-3°, as a byproduct in the oxidation of strychnine by permanganate, can be explained if certain assumptions are made, e.g., the change represented thus —... 

A stereoelectronic argument (62) would suggest quasi-axial addition leading to the right configuration (XLIV) for dihydrostrychninonic acid. The reduction of strychninonic acid to the epimeric strychninolic acid is governed simply by the more ready accessibility of the outer side of the ketone carbonyl group (62). 

Similar oxidation occurs when the benzene ring is absent, as in dihydro-Cig-Hanssen acid (CXLVI), which is oxidized in aqueous potassium bicarbonate at 0° to CXLVII (130). The oxygenation at C-20, C-21, and C-22 in compound CXLIV is of particular interest, because it corresponds to that of the immediate precursor of the key compound in the formation of dihydrostrychninonic acid (XXXVII) this key compound, CXLV, has never been isolated, presumably because of the ease with which it hydrolyzes to dihydrostrychninonic acid (see Section I). 

Oxidations of strychnine straight through to mixtures of strych-ninonic acid (CXLVTII R = H) and dihydrostrychninonic acid (XXXVII) and the parallel oxidation of brucine have, of course, been worked out in great detail in the oxidation of strychnine, the best yield is 24% of a 25 1 mixture of strychninonic and dihydrostrychninonic acids (131). About 1% of 12-hydroxydihydrostrychninolone-a (XLVIII)... 

This reagent has been used very frequently, either with barium hydroxide or with formic acid, to oxidize a-keto acids as either acids or lactams thus, strychninonic acid (XXXVIII) is converted by H2O2/ Ba(OH)2 into CLXX, in this case with concurrent base-catalyzed elimination of the glycolic acid residue (140). Very similar is the oxidation of dihydrostrychninone (CLXXI) in formic acid and hydrogen peroxide... 

Brucinone, the ketone of brucinolone-a, contrary to expectation is not readily available, if at all, from the alkaline cleavage of brucinonic acid (61, 100) or from its derivatives (oxime (95, 105), hydrazone (100), phenyl-hydrazone (102), and semicarbazone (102)). However, strychninone (236) and dihydrostrychninone (190, 232, 236) (XXVII) have been prepared by another method. The secondary hydroxyl of strychninolone-a and of dihy-drostrychninolone-a (from the catalytic reduction of strychninolone-a) has been oxidized (CrOs) to a ketonic group. 

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