Azomethine ylides cyano group

Azomethine ylides containing a leaving group can also be produced by the standard tautomerization route (e.g., species 60 with a cyano group on the ylide carbon). These species (e.g., 60 [R =Ph, PhCO,PhCH=CH R = H,Ph]) reacted with maleimides and with fiimarate, maleate, and acrylate esters to give adducts 61, which readily eliminated hydrogen cyanide (33). 

Padwa and coworkers found that a-cyanoaminosilane 12a is a convenient synthon for azomethine ylide 15 which is extensively used in heterocyclic synthesis [7]. AgP has been adopted to generate the ylide 15 from 12a for the preparation of pyrrolidine derivative 14 (Sch. 4). Various dipolarophiles including A-phenylmaleimide (13) can be used for the cycloaddition. When iV-[(trimethylsilyl)methyl]-substituted indole 16 is reacted with AgP in the presence of maleimide 13, pyrrolo[l,2-a]indole 17 is formed in good yield, retaining the CN group [8]. A silver-bonded carbonium ion is assumed to be a reactive intermediate. Reaction of a cyano-substituted azomethine ylide, derived from (silylmethylamino)malononitrile 12b and AgP, with methyl propiolate (18) provides 3-carbomethoxy-A-benzylpyrrole (19) [9]. Epibatidine, a novel alkaloid, was successfully synthesized by employing the [3 + 2] cycloaddition of azomethine ylide with electron-deficient alkenes as a key step [10]. 

Although very important for understanding the mechanism of the process, these reactions are of limited usefulness as synthetic methods. In the case of cyclic alkenes, c.g., AT-methyl maleinimidcs or maleic anhydride, high endo selectivity is achieved in the reaction with iV-un-substituted or A -metalated azomethine ylides bearing an electron-withdrawing substituent (carbonyl, cyano) at one carbon and an aryl, acyl, or 1-alkenyl group at the other. 

---