The retro Grignard addition reaction revisited: the reversible addition of benzyl reagents to ketones

The Grignard addition reaction is known to be a reversible process with allylic reagents, but so far the reversibility has not been demonstrated with other alkylmagnesium halides. By using crossover experiments it has been established that the benzyl addition reaction is also a reversible transformation. The retro benzyl reaction was shown by the addition of benzylmagnesium chloride to di-tert-butyl ketone followed by exchange of both the benzyl and the ketone moiety with another substrate. Similar experiments were performed with phenylmagnesium bromide and tert-butylmagnesium chloride, but in these two cases the Grignard addition reaction did not show any sign of a reverse transformation.     

Highly enantioselective Michael addition of cyclic ketones to chalcones catalyzed by pyrrolidine-based imides

An efficient procedure for asymmetric Michael addition reaction of cyclic ketones with low activated chalcones catalyzed by pyrrolidine-based phthalimide and 1,8-Naphthalimide catalysts was developed. The corresponding products were obtained in high yields with high diastereoselectivities (up to 99:1 dr) and high enantioselectivities (up to 96% ee) under mild conditions.     

Microwave-accelerated conjugate addition of aldehydes to α,β-unsaturated ketones

Aldehydes undergo smooth conjugate addition to α,β-unsaturated ketones in the presence of 5-(2-hydroxyethyl)-1,3-thiazolium halides and DBU adsorbed onto the surface of basic alumina under microwave irradiation and solvent-free conditions to afford 1,4-diketones in enhanced yields and reduced reaction times compared to conventional methods.     

Chiral amidophosphane-copper-catalyzed asymmetric conjugate addition of dialkylzinc reagents to nitroalkenes

The copper-amidophosphane-catalyzed asymmetric addition reaction of dialkylzinc reagents with β-aryl and β-alkylnitroalkenes afforded the corresponding nitroalkanes with moderate to good enantioselectivities (54-80% ee). The performance was highly dependent on the reaction procedure where the addition of nitroalkene to the mixture of copper-amidophosphane and dialkylzinc gave higher ee than the addition of dialkylzinc to a mixture of copper-amidophosphane and nitroalkene.     

Chemoselective acylation of some oxidofunctionalised organolithium compounds

Once oxidofunctionalised organolithium compounds 1 (easily prepared by reductive ring opening of isochroman and phthalan by DTBB-catalysed lithiation) were transmetallated with ZnBr₂/CuCN·2LiCl and reacted successively with a carboxylic acid anhydride and an acyl chloride in THF at 0°C, the corresponding differently acylated compounds 4 were obtained after hydrolysis with water. The anhydride performed the O-acylation exclusively and the acyl chloride carried out the C-acylation.     

Addition of halogenoacetic esters to aldehydes and ketones in the presence of Fe(CO)5

The use of complex-forming solvents and variations in the reaction temperature made it possible to prepare α-halogeno β-hydroxy carboxylic esters upon addition of halogenoacetic esters to aldehydes and ketones promoted by iron pentacarbonyl. Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 4, pp. 718–720, April, 2000.     

Conjugate addition of pyrroles to α,β-unsaturated ketones using copper bromide as a catalyst

Copper bromide was used as a catalyst for the addition of pyrroles to enones. When both the reactants were used in equimolar amounts, mono and dialkylated products were obtained. However, the use of excess enone furnished only dialkylated products. Thus, copper bromide was shown to be an efficient catalyst for the dialkylation of pyrroles.     

Iodine-catalyzed Michael addition of mercaptans to α,β-unsaturated ketones under solvent-free conditions

A simple and efficient method for the Michael reaction between various mercaptans and α,β-unsaturated ketones using a catalytic amount of iodine (5 mol %) to generate the 1,4-adduct has been reported. The significant features of the iodine catalyzed Michael addition are (a) operational simplicity, (b) inexpensive reagents, (c) high yields of products, (d) the use of relatively low or nontoxic reagents and (e) solvent-free conditions.     

Enantioselective addition of organolithium reagents to quinoline catalyzed by 1,2-diamines

Some enantiomerically enriched 2-substituted-1,2-dihydroquinolines were obtained by the enantioselective addition of organolithium reagents to quinoline. 1,2-Diamines were used as external chiral ligands and enantiomeric excesses up to 64% were obtained.     

A simpler and greener protocol for the preparation of β-acetylamino ketones by a one-pot reaction of aryl aldehydes, enolisable ketones, acetyl chloride and acetonitrile in the presence of zeolite Hβ as a reusable catalyst

β-Acetylamino ketones have been obtained in a one-pot coupling of an aldehyde with an enolisable ketone, acetyl chloride and acetonitrile in the presence of zeolite Hβ as catalyst at room temperature (26-28 °C). The procedure has the advantages of mild workup, circumvention of high temperature and inert atmosphere. The catalyst was found to be recyclable.     

Added-metal-free catalytic nucleophilic addition of Grignard reagents to ketones

On the basis of the investigation of the combinational effect of quaternary ammonium salts and organic bases, an added-metal-free catalytic system for nucleophilic addition reactions of a variety of Grignard reagents to diverse ketones in THF solvent has been developed to produce tertiary alcohols in good to excellent yields. By using tetrabutylammonium chloride (NBu(4)Cl) as a catalyst and diglyme (DGDE) as an additive, this system strongly enhances the efficiency of addition at the expense of enolization and reduction. NBu(4)Cl should help to shift the Schlenk equilibrium of Grignard reagents to the side of dimeric Grignard reagents to favor the additions of Grignard reagents to ketones via a favored six-membered transition state to form the desired tertiary alcohols, and DGDE should increase the nucleophilic reactivities of Grignard reagents by coordination. This catalytic system has been applied in the efficient synthesis of Citalopram, an effective U.S. FDA-approved antidepressant, and a recyclable version of this catalytic synthesis has also been devised.     

Asymmetric addition of achiral organomagnesium reagents or organolithiums to achiral aldehydes or ketones: a review

The enantioselective preparation of chiral secondary and tertiary alcohols via addition of an achiral organomagnesium reagent or an organolithium to an achiral aldehyde or ketone in a chiral medium is reviewed. The review is written in chronological order and contains 113 references to literature through late 2008.     

Development of predictive models of π-facial selectivity; a critical study of nucleophilic addition to sterically unbiased ketones

Quantum chemical calculations at B3LYP/6-31G* and semiempirical levels have been performed on a series of sterically unbiased ketones, where facial differentiation during nucleophilic additions is electronically induced through distal functional groups. The face selectivity data for fifty-four substrates representing nine different skeleta were computed and compared with the available experimental data on thirty-eight of them. The predictive abilities of various computational methods such as, charge model, hydride model, LiH transition state model, Cieplak hyperconjugation effect estimated by NBO analysis and the cation complexation model have been evaluated. A comparison of the computed and experimental face-selectivity data indicates that the hydride model and the LiH transition state model at the semiempirical levels are the best choices to predict diastereoselectivity. Unexpectedly, the performance of charge, hydride and LiH transition state models are inferior at the B3LYP level compared to the semiempirical methods in predicting the facial selectivities. On the other hand, the Cieplak type hyperconjugation evaluated using the NBO analysis, and cation complexation model are less reliable despite the fact that these two involve higher (B3LYP/6-31G*) level calculations. The inadequate performance of the charge model, NBO and the cation complexation models were traced to their emphasis on only one or two factors which are responsible for stereodifferentiation and undermining of the other subtle aspects involving a combination of orbital and electrostatic effects. On the other hand, the hydride and LiH transition state models, at semiempirical levels, provide reliable results to model the face-selectivities.