Chiral acyl radical equivalents: 5-exo cyclization of conformationally constrained 1,3-dioxolanyl radicals

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.

Thiophenol-Mediated Hydrogen Atom Abstraction: An Efficient Tin-Free Procedure for the Preparation of Cyclopentane Derivatives

[reaction: see text] An efficient procedure for running a cascade reaction involving 1,5-abstraction of a hydrogen atom followed by a radical cyclization is reported. Alkenyl radicals are generated from easily available terminal alkynes and thiophenol. This procedure eliminates the need of using the toxic tributyltin hydride and gives a greater amount of radical translocation products.

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.