Alkenes pyrrolizidine derivatives

Dipolar addition to nitroalkenes provides a useful strategy for synthesis of various heterocycles. The [3+2] reaction of azomethine ylides and alkenes is one of the most useful methods for the preparation of pyrolines. Stereocontrolled synthesis of highly substituted proline esters via [3+2] cycloaddition between IV-methylated azomethine ylides and nitroalkenes has been reported.147 The stereochemistry of 1,3-dipolar cycloaddition of azomethine ylides derived from aromatic aldehydes and L-proline alkyl esters with various nitroalkenes has been reported. Cyclic and acyclic nitroalkenes add to the anti form of the ylide in a highly regioselective manner to give pyrrolizidine derivatives.148... 

Bicyclic isoxazolidine 63 was obtained in good yield by 1,3-DC of D-arabinose-derived nitrone 61 and D-mannitol-derived alkene 62 and then used as common intermediate for a divergent synthesis of polyhydroxy-indolizidines and -pyrrolizidines. Iminosugars 64 and 65 proved to be good inhibitors of some commercially available glycosidases (14JOC10786). 

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... 

The amino derivatives of rare-earth metals follow a distinct mechanism involving direct insertion of the allene or alkene into the metal-nitrogen bond (Scheme 6.73). With the less-reactive lanthanum complex 6.215, amine 6.214 underwent insertion of only the allene, giving a pyrrolidine product 6.216 as the trans isomer. On the other hand, using the more-reactive samarium complex 6.217, tandem allene and alkene insertion occurred giving, after hydrogenation, the pyrrolizidine alkaloid, xenovenine 6.189, A closely related synthesis of this alkaloid is in Scheme 6.59. Other syntheses may be found in Scheme 6.65, and Scheme 9.46. 

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