Abstract
AbstractThe course of the reactions involved in the process of degradation of strychnine (1) to Wieland‐Gumlich aldehyde (WGA) (2), first performed by Wieland, Kaziro & Gumlich, has been elucidated. 23‐Isonitrosostrychnine hydrochloride (9a) upon treatment with thionyl chloride undergoes a fragmentation (2nd order Beckmann rearrangement), thus furnishing N(a)‐cyanoformyl‐WGA hydrochloride (14a). On heating in an acidic medium, the latter compound is transformed — at least partially via the cyclic urethane 15 — into WGA (2), which is an important keyintermediate in the syntheses of strychnine and curare alkaloids. The compound 2 can now be obtained in high purity and good yield.A corresponding degradation has been realized with quaternary analogues (27 → 3) as well as with 10‐chlorostrychnine (58 → 62).10‐Chlorostrychnine (58) was prepared by chlorination of strychnine with chlorine in conc. hydrochloric acid according to Leuchs & Steinborn. As by‐products of the reaction, 10, 15‐dichlorostrychnine (59) and 10, 15, 19‐trichlorostrychnine (60) could be identified.Starting from WGA a series of derivatives have been prepared. Special mention is made of the two epimeric methyl ethers 18 and 19. The absolute configuration at the centre 17 of WGA and of these two substances has been established by optical comparisons of 3 epimeric pairs.The methyl ether 18, by‐product «B», is obtained if methanol is used in working up the Beckmann rearrangement products of 23‐isonitrosostrychnine hydrochloride (9a).A second by‐product, «A», results by working up under alkaline conditions. This compound has the structure 44 with inverted configuration at centre 16. Degradation of 44 under controlled conditions leads either to WG‐diol (42) or to 16‐epi‐WG‐diol (51).Besides «Az.rdang; and «B» a series of by‐products and intermediates (16, 17, 11a, 22. 23, 24 and 25) could be detected in the course of the process of strychnine degradation.
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