Cyclization of unsaturated amides with triflic anhydride and samarium diiodide

Direct reductive coupling of secondary amides: chemoselective formation of vicinal diamines and vicinal amino alcohols

We report the first direct and chemoselective reductive homocoupling reaction of secondary amides and cross-coupling reaction of secondary amides with ketones. This method relies on the direct generation of α-amino carbon radicals from amides.

Cyano(ethoxycarbonothioylthio)methyl Benzoate: A Novel One-Carbon Radical Equivalent

[reaction: see text] Cyano(ethoxycarbonothioylthio)methyl benzoate 3 has been prepared and shown to be an excellent one-carbon radical equivalent that can be applied for the introduction of an acyl unit via xanthate transfer radical addition to olefins. The corresponding adducts can be further elaborated. A rare 1,5-nitrile translocation was also observed during the study.

Can Decarbonylation of Acyl Radicals Be Overcome in Radical Addition Reactions? En Route to a Solution Employing N-Acyl Oxazolidinones and SmI2/H2O

The application of acyl radicals in radical addition reactions in the absence of a CO atmosphere is generally limited to aryl or alpha-unsubstituted alkyl acyl radicals due to competing decarbonylations where the rate constant for this degradation process surpasses 104 s-1. In this work, a potential solution to avoid the problem of decarbonylations is presented employing N-acyl oxazolidinones which are reduced to acyl radical equivalents in the presence of samarium diiodide and water. In the company of an acrylamide, acrylate, or acrylonitrile, the product from a formal acyl radical addition is obtained in yields up to 87%. Examples are given where the decarbonylation rate constants even exceed 108 s-1. It is proposed that the reaction proceeds via a ketyl-like intermediate.

SmI2 reduced thioesters as synthons of unstable acyl radicals: direct synthesis of potential protease inhibitors via intermolecular radical addition

Aromatic alpha-heterosubstituted thioesters were found to undergo radical 1,4-addition reactions to a series of alpha,beta-unsaturated amides and one ester when subjected to the single electron reducing agent, samarium diiodide, at -78 degrees C. These thioesters derived from alpha-amino acids represent a synthetically useful synthon of unstable acyl radicals. This reaction conveniently provides access to gamma-ketoamides and esters in yields up to 90%, structures that are common in various protease inhibitors derived from peptides. Examples with acryloyl and methacryloyl derivatives of alpha-amino acids and dipeptides lead directly to tri- and tetrapeptide mimetics possessing the gamma-ketoamide functionality. No epimerization was observed with the mild conditions used for these reactions.

Decarbonylative radical cyclization of alpha-amino selenoesters upon electrophilic alkenes. A general method for the 6-azabicyclo[3.2.1]octane synthesis

alpha-Amino selenoester-tethered electronically poor alkenes on treatment with tributyltin hydride or TTMSS undergo intramolecular radical cyclization to provide 6-azabicyclo[3.2.1]octanes through 1-aminomethyl radical intermediates.