Environmentally friendly TPDS-mediated free radical ring expansion of α-haloalkyl cyclic β-keto esters

Strategy for Overcoming Full Reversibility of Intermolecular Radical Addition to Aldehydes: Tandem C-H and C-O Bonds Cleaving Cyclization of (Phenoxymethyl)arenes with Carbonyls to Benzofurans

An intermolecular addition of carbon radicals enabled by a cascade radical coupling strategy is developed. It includes an intermolecular alkyl radical addition to a carbonyl group followed by an intramolecular alkoxy radical addition to haloarenes and produces substituted benzofurans in high yields. The radical nature of this reaction is explored by radical trapping experiments and EPR analysis. The mechanism is investigated by KIE experiments and control experiments. This method could provide rapid and practical access to the key intermediate of TAM-16, a safe and potent antibacterial agent for treating tuberculosis, and, therefore, is of great importance for organic synthesis and the pharmaceutical industry.

Organic dye-catalyzed radical ring expansion reaction

Herein, we reported an attractive method for synthesizing medium-sized rings that are catalyzed by erythrosine B under fluorescent light irradiation. This synthetic approach featured mild conditions, a facile procedure, a broad substrate scope, and moderate-to-good yields.

Herein, we reported an attractive method for synthesizing medium-sized rings that are catalyzed by erythrosine B under fluorescent light irradiation.

Approach to 3-Aminoindolin-2-ones via Oxime Ether Functionalized Carbamoylcyclohexadienes

O-Benzyloxime ether substituted amidocyclohexadienes were prepared in three steps in good yields from 2-aminoacetophenone. EPR spectroscopic observations and product analyses showed that peroxide-induced decompositions of model compounds led to indolin-2-ones with benzyloxyaminyl substitution at their 3-positions. The cyclization steps were very rapid and took place regioselectively at the C-atoms of the C=N bonds, by 5-exo ring closures. An O-trityloxime ether analogue was also prepared. The cyclohexadienyl intermediate smoothly yielded an alkoxylaminyl radical again by rapid 5-exo-cyclization. However, ring closure was quickly followed by another beta-scission step that released the persistent trityl radical and a 3-nitrosoindolin-2-one derivative. EPR spectroscopic evidence showed that the nitroso compound trapped other transient intermediates to afford a series of nitroxides. GC-MS analyses of products formed in reactions including methyl thioglycolate indicated that 1-benzyl-3-methyl-1,3-dihydro-2H-indol-2-one was derived from the indolinone moiety.

Zinc- and Indium-Mediated Ring-Expansion Reaction of α-Halomethyl Cyclic β-Keto Esters in Aqueous Alcohol

Radical ring-expansion reaction of various alpha-halomethyl cyclic beta-keto esters and alpha-halomethyl benzocyclic beta-keto esters and chain-extension reaction of alpha-halomethyl beta-keto esters with zinc powder and indium powder in refluxing aqueous alcohol were carried out to generate the corresponding ring-expansion and chain-extension products. As the results indicate, it was found zinc powder was more effective than indium powder to give the corresponding ring-expanded products in quite good yields. Moreover, the addition of zinc bromide as Lewis acid showed an increase of the yields, depending on the substrates. The present reaction conditions are highly effective, simple, and environmentally friendly.

Silylated cyclohexadienes as new radical chain reducing reagents: preparative and mechanistic aspects

Various silylated 1,4-cyclohexadienes are presented as superior tin hydride substitutes for the conduction of various radical chain reductions. Debrominations, deiodinations, and deselenations can be performed using these environmentally benign reagents. Furthermore, Barton-McCombie-type deoxygenations using silylated cyclohexadienes are described. Radical cyclizations, ring expansions, and Giese-type addition reactions with the new tin hydride substitutes are presented. The polymerization of styrene can be regulated using silylated cyclohexadienes. Rate constants for hydrogen atom abstraction from two 1-silyl-cyclohexadienes by primary C-radicals were determined. The effects of the cyclohexadiene substituents on the reaction outcomes are discussed. Finally, qualitative EPR experiments on silyl radical expulsion from silylated cyclohexadienyl radicals are presented.