Corydalic acid methyl ester, synthesis

As a part of the total synthesis of (+ )-corydalic acid methyl ester (12), a reaction of a cyclic enolate with an imine has been applied. The 2-toluamide enolate 9, which in this case is substituted at the methyl group, adds stereospecifically to imine 10, affording mainly tram-iso-quinolone 11 with a d.r. (transjds) > 95 525. 

The Hofmann degradation product 252 used for a synthesis of corynoline (254) was again a useful starting material for ( )-corydalic acid methyl ester (8). It was reduced with sodium cyanoborohydride to the trans derivative 10 as a major product, which was converted to 8 via acetal 268 and aldehyde 269 (143). 

In Table IV some physical data and spectral characteristics of 6,7-secoberbines are listed. Only methyl corydalate (55) is optically active. Formula 55 presents the spatial structure of this compound, deduced by Nonaka et al. (65) and confirmed by Cushman et al. by both correlation with (+)-mesotetrahydrocorysamine (72) (<5S) and total synthesis (69). It is difficult to find common characteristic features in both the mass and H-NMR spectra of these alkaloids because they differ significantly from each other in their structures. On one hand, corydalic acid methyl ester (55) incorporates a saturated nitrogen heterocycle, while the three aromatic bases (56-58) differ in the character of the side chain nitrogen. For example, in mass fragmentation, ions of the following structures may be ascribed to the most intensive bands in the spectrum of 55 ... 

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