Pyrrolizidine alkaloids dehydrogenation

The preparation of the dihydropyrrolizine analogues [e.g. (30)] of the unsaturated pyrrolizidine alkaloids has also been studied comprehensively. Several procedures have been shown to be effective in one or more instances, e.g. oxidation by manganese dioxide in chloroform, dehydrogenation by... 

Several of the synthanecine derivatives, and in particular the carbamates of synthanecine A (11), were shown to be metabolically dehydrogenated to pyrrole derivatives by rat liver in vivo and to cause toxic effects in animals very similar to, if not identical with, those produced by the toxic pyrrolizidine alkaloids. The synthetic pyrrole relatives of the synthanecines, like the pyrrolic analogues of the toxic alkaloids, were also capable of cross-linking DNA in vitro, and of causing cytotoxic effects in rats. ... 

Rh catalyses the hydrosilylation of alkenes and the dehydrogenative silylation of 1,5-dienes and alkynes, and the silylcarbonylation of alkynes to give p-silylacrylaldehydes with exceptional stereocontrol , ketones and enones give silyl enol ethers, 1,3-cyclobutane dione gives 3-hydroxycyclobutanone, and assists in the silylformylation of ethynyl pyirolidone derivatives to give pyrrolizidine alkaloids, and epoxides to give p-siloxy aldehydes, and... 

Mattocks 205) has prepared several substituted 3-pyrrolines [e.g. synthanecine A (101)] which are monocyclic analogues of the pyrrolizidine alkaloids. Some of these derivatives [particularly the carbamate (102) of synthanecine A] can be dehydrogenated in animals to the corresponding pyrrole derivatives, which act as alkylating agents, and show similar toxic effects to those produced by pyrrolizidine alkaloids. 

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