Piperidides reduction

The same reaction sequence performed in methanol affords a mixture of diastereo-mers of the phosphorylated phosphinic ester 48b, of which one pure isomer can be isolated32 . In the presence of piperidine, reductive elimination of nitrogen 28,29) from 45 to give bis(diphenylphosphoryI)methane competes with the prevailing formation of the phosphinic piperidide 48c32). Expected trapping of 47 by [2 + 2]-cycloaddition with benzaldehyde fails to occur in place of 1,2k5-oxaphosphetanes, products are obtained which arise mainly by way of the benzoyl radical32,33). 

In analogy to the preparation of the cyclopropanone hemiacetal 3 (vide supra, Eq. (1)7), reductive cyclization of the piperidide of 3-chloropropionic acid 193 with sodium in ether in the presence of ClSiMe3, gave the 1-piperidino-l-trimethylsilyloxy-cyclopropane 194 a which was converted to the cyclopropanol 194 b upon treatment with methanolic tetrabutylammonium fluoride. Both 194 a and 194 b can be used for the ready generation of cyclopropane derivatives thus the silyl ether 194a could be reacted directly with the vinylic Grignard reagents 195 to provide the vinyl cyclopropane derivative 196, (Eq. (61)128). 

Allomatridine has also been synthesised by mercuric acetate oxidation of lupinoyl piperidide (9c) followed by reduction with sodium borohydride the product was mainly racemic starting material, but a small amount (3.4%) of an isomer (24) of allomatrine was obtained, which was converted into allomatridine (19) by reduction with lithium aluminium hydride. 

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