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2 6 in conjunction with the occurrence of m/e 58 and m/e 72 ions in the mass spectrum when, considered together with 'H-NMR signals indicative of a veratryl ring, suggested that the alkaloid should be represented by structure 45 (without stereochemical details being implied). Confirmatiom of the structural assignment was obtained by borohydride reduction of (-)-3'-methoxy-4'-O-methyljoubertiamine (42)to pair of epimeric alcohols (45 and 46). The former proved identical to that of the natural product.
04 6, whereas the olefinic hydrogen signals exhibited a more typical AB quartet pattern in the a-alcohol (46). A summary of these and other reactions relating to the assignment of the structure of Y-methoxy-4'-O-methyljoubertiamineappears in Scheme 10. H I 1111111111111 Me,N \ 1111111111111 46 HZPt 111111111111 Me,N gH+ ,g ,gH+ ,g;H (yeiB"I I 1111111111111 I 'Me 47 45 SCHEME 10. Chemical transformations of 3'-methoxy-4'-O-methyljoubertiamk (42)and the stereochemirtry of ( -)-3'-methoxy-+-O-methyljoubertiamho1(45).
There are several points of interest in the synthesis which should be mentioned. The application of the seldom-used Nef reaction for the introduction of the carbonyl group was not without initial problems. Poor yields of the ketone were obtained until it was recognized that the sodium aci-salt of the nitro compound was sensitive to oxygen and heat. Introduction of a suitable two-carbon fragment necessary for the construction of the pyrrolidine ring was also not without difficulty. Attempts to alkylate the ketone (step 4) with bromoacetate, chloroacetonitrile, and N-methylethylenimine were unsuccessful.