Mg-promoted mixed pinacol coupling

Mg-promoted reduction of a mixture of aromatic ketones (or imines) and aliphatic carbonyl compounds in N,N-dimethylformamide (DMF) brought about unique mixed pinacol type of cross coupling to give unsymmetrical vicinal diols (or amino alcohols) or α-hydroxyketones in good to moderate yields. The reaction may be initiated by electron transfer from magnesium metal to an aromatic carbonyl compound possessing a less negative reduction potential. The difference of reduction potential between aromatic ketones (or imines) and aliphatic carbonyl compounds was found to be one of the important key factors in this selective cross coupling.     

Regioselective synthesis of bis(silyl enol ethers) and bis(conjugated enones) through electron transfer from Mg metal

Treatment of α,β-unsaturated ketones with Mg metal in the presence of trimethylsilyl choride (TMSCl) brought about facile and regioselective reductive dimerization to give the corresponding bis(silyl enol ethers), 1,6-bis(trimethylsilyloxy)-1,5-dienes. Similar Mg-promoted reductive dimerization of 1,3-cyclic diketones in the presence of TMSCl followed by acid-catalyzed hydrolysis led to selective formation of the corresponding 1,6-diketo-2,4-dienes in moderate to good yields.     

Mg-promoted C-trifluoroacetylation of benzophenone

Mg-promoted reduction of benzophenones in the presence of ethyl trifluoroacetate and trimethylchlorosilane in N-methyl-2-pyrrolidinone afforded the corresponding cross-coupling products, which were easily transformed into C-trifluoroacetylated compounds of benzophenones through desilylation by tetrabutylammonium fluoride.     

Direct reductive amination of carbonyl compounds using bis(triphenylphosphine) copper(I) tetrahydroborate

A direct reductive amination protocol for aldehydes/ketones using bis(triphenylphosphine) copper(I) tetrahydroborate as a novel reducing agent in the presence of sulfamic acid has been developed. The reagent chemoselectively reduces the imine moiety and does not affect other reducible functionalities such as chloro, nitro, cyano and methoxy.     

Sulfonation of aromatic and heterocyglic compounds with bis(trimethylsilyl) sulfate

Conclusions A new sulfonating agent, namely bis(trimethylsilyl) sulfate, was found, which easily sulfonates benzene derivatives that contain substituents of the first type, and also thiophene. Benzene and nitrobenzene do not react with bis (trimethylsilyl) sulfate.Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No. 10, pp. 2340–2341, October, 1977.     

Radical promoted cyclizations of aromatic carbonyl compounds to benzopyrans using titanocene(III) chloride

Aromatic carbonyl compounds undergo smooth intramolecular radical cyclization with alkenes or alkynes using titanocene(III) chloride to furnish the corresponding benzopyrans. The radical initiator, Cp₂TiCl, was prepared in situ from commercially available titanocene dichloride (Cp₂TiCl₂) and zinc dust in THF under argon.     

Synthesis of azo compounds by nanosized iron-promoted reductive coupling of aromatic nitro compounds

Treatment of a variety of aromatic nitro compounds with the active-iron based reducing system composed of FeCl₂·4H₂O, an excess of lithium powder and a catalytic amount of 4,4′-di-tert-butylbiphenyl (DTBB, 5 mol %) in THF at room temperature, led to the formation of the corresponding symmetrically substituted azo compounds in good yield, resulting from a reductive coupling process. Some other functionalities including carbonyl, halogen, amino and hydroxyl groups, demonstrated to be compatible with the reaction conditions, giving none reduced or coupled by-products. In all cases, the azo compounds formed have not experienced over-reduction to the corresponding hydrazo or amino derivatives even upon prolonged heating or using an excess of the reducing system.     

Reactions of (2,3-dimethylenetetramethylene)bis(dipropylborane) with carbonyl compounds

(2,3-Dimethylenetetramethylene)bis(dipropylborane) (1) prepared by borylation of 2,3-dimethylbutadienediyl dipotassium reacts with ketones to form symmetrical diols in a yield of 46–73%. [4+2]-Cycloaddition reactions of diborane1 with 1,2-dicarbonyl compounds proceed highly stereospecifically, affording onlycis-isomers of 4,5-dimethylenecyclohexane1, 2-diols.Translated fromIzvestiya Akademii Nauk, Seriya Khimicheskaya, No. 1, pp. 155–159, January, 1993.     

Samarium-induced convenient reductive dimerization of aromatic ketones in aqueous methanol: a mechanistic approach

Samarium metal has been used for the reductive dimerization of aromatic ketones in the presence of additives; the most probable mechanism has been advanced to explain the diastereoselectivity of this dimerization reaction.     

Facile synthesis of multifunctionalized allenes by magnesium-promoted reductive silylation of aromatic conjugated ynones

Mg-promoted reductive silylation of 4-phenyl-3-butyn-2-one in N,N-dimethylformamide (DMF) in the presence of chlorotrimethylsilane brought about double silylation at the β-carbon and oxygen atoms of the carbonyl group to give a multifunctionalized allene with a vinylsilane moiety and a silyl enol ether moiety. A variety of allenes can be synthesized through this simple methodology. Acid-catalyzed hydrolysis of an allene derived from the trimethylsilylation of 4-phenyl-3-butyn-2-one resulted in the formation of the corresponding benzalacetone with a trimethylsilyl group at the β-position of the carbonyl group in high yield.     

Samarium/N-bromosuccinimide-induced reductive dimerization of carbonyl compounds

Stereoselective reductive coupling of carbonyl compounds has been achieved using samarium/N-bromosuccinimide in methanol. The combination of these agents has proved a powerful addition to the arsenal of samarium-based reductants currently utilized.     

Gallium-induced Barbier coupling of carbonyl compounds with allyl iodide

Gallium metal readily prompted the allylation of aldehydes and ketones with allyl iodide. α, β-Unsaturated carbonyl compounds underwent only 1,2-addition.     

SmI2-promoted tandem desulfurization and reductive coupling reactions of aromatic lactams with carbonyl compounds

Treatment of sulfur-substituted aromatic lactams with carbonyl compounds in the presence of samarium(II) diiodide was found to undergo novel tandem desulfurization and reductive coupling reactions to generate -hydroxyalkylated lactams in high yield. Stereochemistry of the coupling products was researched and the results that decreasing the steric bulkiness of the N-substituents as well as raising the reaction temperature leads to an increase of the erythro-selectivity were observed. The mechanistic origins of this stereoselectivity are also briefly documented.     

Molecular mechanics (MM4) calculations on carbonyl compounds part I: aldehydes

Aliphatic aldehydes have been studied with the aid of the MM4 force field. The structures, moments of inertia, vibrational spectra, conformational energies, barriers to internal rotation, and dipole moments have been examined for six compounds (nine conformations). MM4 parameters have been developed to fit the indicated quantities to the wide variety of experimental data. Ab initio (MP2) and density functional theory (B3LYP) calculations have been used to augment and/or replace experimental data, as appropriate. Because more, and to some extent, better, data have become available since MM3 was developed, it was anticipated that the overall accuracy of the information calculated with MM4 would be better than with MM3. The best single measure of the overall accuracy of a force field is the accuracy to which the moments of inertia of a set of compounds (from microwave spectroscopy) can be reproduced. For all of the 20 moments (seven conformations) experimentally known for the aldehyde compounds, the MM4 rms error is 0.30%, while with MM3, the most accurate force field presently available, the rms error over the same set is 1.01%. The calculation of the vibrational spectra was also improved overall. For the four aldehydes that were fully analyzed (over a total of 78 frequencies), the rms errors with MM4 and MM3 are 18 and 38 cm^?1, respectively. These improvements came from several sources, but the major ones were separate parameters involving the carbonyl carbon for formaldehyde, the alkyl aldehydes and the ketones, and new crossterms featured in the MM4 force field that are not present in the MM3 version. © 2001 John Wiley & Sons, Inc. J Comput Chem 22: 1396–1425, 2001     

Palladium(II)-catalyzed carboxylation of benzene and other aromatic compounds with carbon monoxide under very mild conditions

Aromatic compounds such as benzene, toluene, chlorobenzene, anisole, and naphthalene were carboxylated by palladium(II) acetate catalyst with carbon monoxide in the presence of potassium peroxodisulfate in trifluoroacetic acid (TFA) at room temperature under atmospheric pressure. The aromatic carboxylic acids were formed in good yields; for example, the carboxylation of benzene with carbon monoxide proceeds quantitatively under the optimal conditions.     

Supercritical fluid extraction-high performance liquid chromatography on-line coupling: Extraction of some model aromatic compounds

Summary An SFE-HPLC system has been tested with a simple model aromatic mixture on spiked silica. The spiked silica was extracted with pure CO₂ and the extract retained in a trap packed with C18 material. Quantitative separation and reproducity have been investigated and are reported.     

Supercritical fluid extraction-high performance liquid chromatography on-line coupling: Extraction of some model aromatic compounds

Summary An SFE-HPLC system has been tested with a simple model aromatic mixture on spiked silica. The spiked silica was extracted with pure CO₂ and the extract retained in a trap packed with C18 material. Quantitative separation and reproducity have been investigated and are reported.     

Synthetic applications of beta-fluoroalkylated alpha,beta-unsaturated carbonyl compounds

Beta-fluoroalkylated alpha,beta-unsaturated carbonyl compounds constitute efficient building blocks for the synthesis of complex fluorinated compounds. As the fluorinated moiety generally increases their reactivity, it also brings important modifications which can change the chemical behavior and selectivity. Their use has been already largely demonstrated. Nevertheless, the synthetic potential has not yet been fully explored and, consequently should play an important role in the design of new sophisticated fluorinated molecules. Nevertheless, it shall be important to develop new synthetic methods to enlarge their availability and their diversity.     

A metal-catalyst-free oxidative coupling of anilines to aromatic azo compounds in water using bleach

A simple route toward the synthesis of symmetrical and unsymmetrical aromatic azo compounds through oxidative coupling of anilines using widely available NaOCl is presented. This metal catalyst-free protocol is performed in water and affords the desired products in high yields.