123027-08-7Relevant academic research and scientific papers
Photocatalytic Hydromethylation and Hydroalkylation of Olefins Enabled by Titanium Dioxide Mediated Decarboxylation
Zhu, Qilei,Nocera, Daniel G.
, p. 17913 - 17918 (2020/12/04)
A versatile method for the hydromethylation and hydroalkylation of alkenes at room temperature is achieved by using the photooxidative redox capacity of the valence band of anatase titanium dioxide (TiO2). Mechanistic studies support a radical-based mechanism involving the photoexcitation of TiO2 with 390 nm light in the presence of acetic acid and other carboxylic acids to generate methyl and alkyl radicals, respectively, without the need for stoichiometric base. This protocol is accepting of a broad scope of alkene and carboxylic acids, including challenging ones that produce highly reactive primary alkyl radicals and those containing functional groups that are susceptible to nucleophilic substitution such as alkyl halides. This methodology highlights the utility of using heterogeneous semiconductor photocatalysts such as TiO2 for promoting challenging organic syntheses that rely on highly reactive intermediates.
Intramolecular Nucleophilic Addition to Unsaturated Carbon. Dependence of Cyclization Efficiency on the Method of Carbon-Carbon Bond Cleavage Utilized To Generate the Reactive Species
Paquette, Leo A.,Gilday, John P.,Maynard, George D.
, p. 5044 - 5053 (2007/10/02)
The following three reactions have been studied for the purpose of comparing their intrinsic ability to generate carbanionic intermediates capable of intramolecular cyclization: (a) the Haller-Bauer cleavage of ketones 15a and 15b, as well as the (S)-(+)-antipode of 15a (viz. 47); (b) the base-promoted cleavage of 1,1-diarylcarbinols 16a and 16b; (c) decarboxylative elimination within the methyllithium adducts of carboxylic acids 17a and 17b.The Haller-Bauer process proceeds predominantly via carbanion intermediates, which most often experience protonation to give 18 an d 21.Cyclization becomes possible, however, under certain circumstances and reaches a maximum of 33percent with NaNH2 in benzene.Using (+)-47 as a probe, it has been possible to ascertain that 56percent of the reactive intermediate molecules racemize and that only the racemic species generates cyclic product.On the other hand, the Cram-type cleavages of 16a and 16b proceed mainly by homolytic cleavage to generate the benzophenone radical anion and free-radical intermediate.The latter dimerize, capture solvent, and abstract hydrogen to varying degrees depending upon counterion and solvent.Finally, reactions of type c are the most efficient at effecting intramolecular ring closure.
