Alcohols as solvent for the generation and reaction of allylic zinc halides with aldehydes and ketones

Allylation and propargylation of aldehydes mediated by in situ generated zinc from the redox couple of Al and ZnCl2 in 2N HCl

A simple one pot allylation and propargylation of aldehydes mediated by zinc(0), which is in situ generated from the redox couple of Al and ZnCl₂ in 2N HCl, is demonstrated to afford the corresponding homoallyl and homopropargyl alcohols with excellent yields.

Electrophilic [N-F]+ catalysed asymmetric allylation of (E)-N,1-diphenylmethanimine

New efficient catalysts based on electrophilic N-fluoro quaternary ammonium salts are reported for catalytic allylation of (E)-N,1-diphenylmethanimine. The chiral version of the catalyst based on cinchonidine (F-CD-BF₄ ) shows high catalytic activity with approximately 94% ee and TOF (>800 h^-1 ). The F-CD-BF₄ is prepared from cinchonidine and Selectfluor by one-step transfer fluorination.

Photocatalytic Barbier reaction - visible-light induced allylation and benzylation of aldehydes and ketones

We report a photocatalytic version of the Barbier type reaction using readily available allyl or benzyl bromides and aromatic aldehydes or ketones as starting materials to generate allylic or benzylic alcohols. The reaction proceeds at room temperature under visible light irradiation with the organic dye 3,7-di(4-biphenyl)1-naphthalene-10-phenoxazine as a photocatalyst and DIPEA as sacrificial electron donor. The proposed cross-coupling mechanism of a ketyl- and an allyl or benzyl radical is supported by spectroscopic investigations and cyclic voltammetry measurements.

Waste management in zinc promoted allylation of aldehyde

The waste zinc material in Zn(0) promoted Grignard–Barbier type allylation of aldehydes has been successfully utilized as a reusable material for the adsorption of various dyes and also converted into the corresponding hexagonal wurtzite phase of ZnO.

Cooperative titanocene and phosphine catalysis: accelerated C-X activation for the generation of reactive organometallics

The study presented herein describes a reductive transmetalation approach toward the generation of Grignard and organozinc reagents mediated by a titanocene catalyst. This method enables the metalation of functionalized substrates without loss of functional group compatibility. Allyl zinc reagents and allyl, vinyl, and alkyl Grignard reagents were generated in situ and used in the addition to carbonyl substrates to provide the corresponding carbinols in yields up to 99%. It was discovered that phosphine ligands effectively accelerate the reductive transmetalation event to enable the metalation of C-X bonds at temperatures as low as -40 °C. Performing the reactions in the presence of chiral diamines and amino alcohols led to the enantioselective allylation of aldehydes.

Zn-mediated, Pd-catalyzed cross-couplings in water at room temperature without prior formation of organozinc reagents

Mix in water, stir. That is all that is required in this new approach to sp(3)-sp(2) cross-couplings between an alkyl iodide and an aryl bromide, both potentially bearing functionality. They react under catalysis by Pd(0) in the presence of zinc powder, aided by a nonionic amphiphile, to give the alkylated aromatic. No organic solvents and no heating; just add water.

Development of a highly alpha-regioselective metal-mediated allylation reaction in aqueous media: new mechanistic proposal for the origin of alpha-homoallylic alcohols

This paper described a general method to obtain alpha-adduct homoallylic alcohols using indium, zinc, and tin in water. A new mechanism was proposed to account for the formation of these synthetically difficult-to-obtain molecules. Generally, this method can be performed with a wide range of aldehydes and allylic halides with just 6 equiv of water added, giving the alpha-adduct in high selectivities. To account for the origin of the alpha-homoallylic alcohol, the reaction mechanism was carefully studied using (1)H NMR, a crossover experiment, and the inversion stereochemical studies of 22 beta gamma-adduct homoallylic sterol to the 22 alpha alpha-adduct homoallylic sterol. From the results of mechanism studies, it is possible that two mechanism pathways coexisted in the metal-mediated alpha-regioselective allylation. The metal salts formed from the metal-mediated allylation can catalyze the gamma-adduct to undergo a bond cleavage to generate the parent aldehyde in situ followed by a concerted rearrangement, perhaps a retroene reaction followed by a 2-oxonia[3,3]-sigmatropic rearrangement to furnish the alpha-adduct. The alpha-adduct can also be synthesized via the formation of an oxonium ion intermediate between the gamma-adduct and the unreacted aldehyde. The proposed mechanisms were further supported by experimental findings from the addition of InBr(3) to gamma-adduct under similar conditions.

Quasi-nature catalysis: developing C-C bond formations catalyzed by late transition metals in air and water

This Account outlines the recent efforts of developing catalysis under the ambient conditions of air and water for synthetic purposes from the author's laboratory. The discussions are focused on catalytic reactions (mostly C-C bond formations) other than oxidations via late transition metals. It includes the following aspects: (1) copper-catalyzed C-C bond formations; (2) palladium-catalyzed C-C bond formations; (3) rhodium-catalyzed C-C bond formations; (4) ruthenium-catalyzed olefin isomerizations and C-H activations. The mechanism, limitations, and synthetic applications of these reactions are also discussed.