Of -elaeokanine

Ni alkoxide as a stoichiometric reaction. However, in this reaction the silylnickel alkoxide 76 is formed, and its reductive elimination affords silyl ethers 77 and 78. At the same time, Ni(0) is regenerated to make the reaction catalytic. The formal total synthesis of elaeokanine C (79) was carried out by this reaction [25], Homoallylic alcohol 81 is obtained by the intermolecular reaction of benzaldehyde with the diene 80 and hydrosilane in high regio- and stereoselective manner [26],... 

Wijnberg, B.P, and Speckamp, WN. 1981. a-acyliminium ion synthesis of elaeokanine B. Tetrahedron Lett 22, 5079-5082. 

Simple indolizidine alkaloids from the genus Elaeocarpus were surveyed in Volumes 28 and 44 of this treatise (1,2). The latter survey highlighted a communication on the synthesis of (+ )-elaeokanines A (307) and C (308) by Koizumi and co-workers (289) that has since been published with full experimental details (290). 

Elaeokanine C is also a colourless gum, and is suspected to have the molecular formula C12H21N02, although it has not been subjected to elemental analysis. Its i.r. and n.m.r. spectra are consistent with the structure (18), in which the hydrogen atom at C-7 is equatorial and those at C-8 and C-9 are axially disposed. This gross structure is supported by the reaction of elaeokanine C with ethanolic potassium hydroxide, which affords an a/J-unsaturated ketone having the same retention time on g.l.c. as elaeokanine A.8... 

Elaeokanine D and elaeokanine E, two crystalline alkaloids, are stereoisomers (i.r. and mass spectra) whose n.m.r. spectra are interpreted in terms of the structures (19) and (20) respectively. A sixth alkaloid, elaeokanidine A, contains two nitrogen atoms, but is regarded as a close relative of elaeokanine D in view of the similarity of their n.m.r. spectra. In consequence, elaeokanidine A is formulated as the tricyclic base (21). Finally, two further crystalline alkaloids, elaeokanidines B and C, have been isolated, but not yet extensively investigated. Preliminary data indicate that they are probably stereoisomers of elaeokanidine A. 

In an alternative approach to the nitrone method for the synthesis of Elaeocarpus alkaloids (cf. vol.ll, p.61), a 1,3 dipolar cycloaddition of 1-pyrroline 1-oxlde to a substituted enone gives the isoxazolidine (2), which was converted in a number of steps into the compound (3), the C-7 epimer of elaeokanine C. Oxidation of the epimer (3) afforded the diketone (4), an intermediate in a previously published synthesis of ( )-elaeokanlne C. 

Full details are also available of the structure elucidation of elaeokanines A-E, and elaeokanidines A-C, the leaf alkaloids of E. kaniensis Schltr. further, the structures of elaeokanines A-C have been confirmed by synthesis. The reaction of the diazoketone prepared from butyroyl chloride and diazomethane with pyrrole in the presence of copper powder gave the ketone (9), which was hydrogenated to the basic pyrrolidine ketone (10). Michael addition of ethyl acrylate... 

This synthesis of ( )-elaeokanine C confirms the structure deduced earlier, in particular the cis disposition of hydrogen atoms at C-7 and C-8, since hydrogenation presumably occurs on the enolic form (12a) of the jS-diketone. Curiously, the major product (60%) from this hydrogenation is a crystalline dehydrogenation product, which was assigned the structure (14). 

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