Triphenylphosphine-Catalyzed Preparation of Sterically Congested, Electron-PoorN-Vinylimidazole Derivatives from Acetylenic Esters and Imidazole-Containing NH-Acids

Abstract

Protonation of the highly reactive 1:1 intermediates, produced in the reaction between triphenylphosphine and alkyl acetylenecarboxylates (or ethyl 3-phenyl-2-propynoate), by azathioprine or imidazole leads to vinyltriphenylphosphonium salts, which undergo a Michael addition reaction with a conjugate base to produce phosphorus ylides. Dipotassium hydrogen phosphate, potassium dihydrogen phosphate, and potassium iodide were found to catalyze the conversion of the phosphorus ylides to electron-poor N-vinyl imidazoles in solvent-free conditions under thermal (90 • C, 1 h) conditions. The structural analysis of the products indicated that the reaction is regio-and stereoselective.

Synthesis of N‐Alkenylpurines by Rearrangements of the Corresponding N‐Allyl Isomers: Scopes and Limitations

“…N ‐Vinylation of purines with vinyl acetate and Hg(OAc) 2 may give the 7‐vinylisomer as a by‐products in low yields 7. It was recently reported that azathioprine reacts with esters of acetylenecarboxylates in the presence of PPh 3 to give only the N ‐7‐alkenylated Michael‐type adducts 16. We have shown that the N ‐7 allyl group in N 6 , N ‐7‐diallyladenine can be selectively rearranged to propenyl and used the product in an RCM‐mediated synthesis of the heterocyclic part of asmarines (marine bioactive natural products) 17.…”