Aerobic oxidative α-iodination of carbonyl compounds using molecular iodine activated by a nitrate-based catalytic system

The novel reaction system comprising air/NH₄NO_3(cat.)/I₂/H₂SO_4(cat.) is introduced as a simple, safe, cheap, efficient, and regioselective mediator for direct aerobic oxidative α-iodination of aryl, heteroaryl, alkyl, and cycloalkyl methyl ketones. The reaction system enabled the moderate to quantitative regioselective iodination of a large range of different methyl ketone derivatives including those bearing oxidizable heteroatom (S, N) substituents. Several activated aromatic compounds were also efficiently and selectively iodinated. The practical applicability of the presented reaction system was shown on 20 mmol scale under ambient pressure and 100% conversion of substrate was achieved.     

Selective hydrogenation of α,β-unsaturated carbonyl compounds by rhodium trichloride and aliquat®-336 in a two-phase liquid system

The solvated ion pair [(C₈H₁₇)₃NCH₃]⁺[RhCl₄]⁻, formed from aqueous rhodium trichloride and Aliquat^®-336 in a two-phase liquid system, was shown to hydrogenate α,β-unsaturated ketones and esters selectively at the C-C double bonds. The reduction of benzylideneacetophenone was found to follow first-order kinetics in the substrate only below 0.2 M, and to approach second-order in H₂; at partial pressures of < 0.12 atm. The catalysis also proved to depend on the nature of the solvent, the phase transfer catalyst and the stirring rate. The observed activation energy E_a = 12.4 kcal mol⁻¹ suggests that the process is both chemically and diffusion controlled.     

Sulfoxide-mediated α-arylation of carbonyl compounds

A novel sulfoxide-mediated α-arylation of carbonyl compounds is reported. This reaction proceeds under very mild conditions at room temperature and does not require any transition-metal promoter or catalyst.     

Insertion of cyclopropanes between a carbonyl carbon and an α-carbon of carbonyl compounds with cyclopropylmagnesium carbenoids

The reaction of the lithium enolates of α-aryl carbonyl compounds with cyclopropylmagnesium carbenoids, derived from 1-chlorocyclopropyl p-tolyl sulfoxides with i-PrMgCl at low temperature, resulted in the formation of β-aryl carbonyl compounds bearing a cyclopropane ring at the α-position with one-carbon homologation in variable yields. The reaction was found to be highly stereospecific with respect to the stereochemistry of the cyclopropylmagnesium carbenoids. Mechanism and origin of the stereospecificity of the reaction are also discussed. This is the first example for the insertion of cyclopropanes in between a carbonyl carbon and an α-carbon of carbonyl compounds.     

α-Nitro carbonyl compounds in the synthesis of 2,3-dihydrofurans

A new method for the synthesis of 2,3-dihydrofurans from readily available starting enones and α-nitro carbonyl compounds has been developed. This protocol can provide a novel and effective methodology for the preparation of 2,3-dihydrofurans in a stereoselective fashion. With 1,4-dien-3-ones, 2,3-dihydrofurans and cyclohexenecarboxylates were produced and high chemoselectivity was observed in different solvents.     

A novel olefination of carbonyl compounds with α-bromoacetic ester mediated by tri-n-butylstibine

Tri-n-butylstibine has been found to mediate the olefinatlon of carbonyl compounds by α-bromoacetic ester to give corresponding olefins in good yields.     

Transformation of geniposide into genipin by immobilized β-glucosidase in a two-phase aqueous-organic system

Genipin is the bioactive compound of geniposide and a natural cross-linking agent. In order to improve the preparation process of genipin, the hydrolysis of geniposide to genipin by immobilized β-glucosidase in an aqueous-organic two-phase system was studied. β-glucosidase was immobilized by the crosslinking-embedding method using sodium alginate as the carrier. The optimum reaction temperature, pH value and time were 55 °C, 4.5 and 2.5 h, respectively. To reduce genipin hydrolysis and byproduct production the reaction was carried out in an aqueous-organic two-phase system comprising ethyl acetate and sodium acetate buffer. The product was analyzed by HPLC, UV, IR, and NMR. The yield of genipin was 47.81% and its purity was over 98% (HPLC).     

Synthesis of 3-acylated indoles through iron-catalyzed oxidative coupling of indoles with α-amino carbonyl compounds

A novel iron-catalyzed oxidative coupling of indoles with α-amino carbonyl compounds has been developed. The transformation provides an attractive approach to the synthesis of 3-acylindoles, with the advantages of easily available starting materials and high functional group tolerance. Furthermore, control experiments imply that a radical process maybe involved in this reaction.     

α-Fluoroalkylation of carbonyl compounds mediated by a highly reactive alkyl-rhodium complex

Treatment of silyl enol ethers of various carbonyl compounds with Et₂Zn and fluoroalkyl halides (R_f-X) in the presence of RhCl(PPh₃)₃ in DME gave the corresponding α-R_f carbonyl compounds. A highly reactive alkyl-rhodium complex which was derived from RhCl(PPh₃)₃ and Et₂Zn must be crucial in this reaction by accelerating the reaction rate and improving the yields dramatically. This reaction overcomes difficulties on the synthesis of α-R_f carbonyl compounds due to inverse polarization of R_f-X.     

Convenient and rapid synthesis of α-aminonitriles starting directly from nitro compounds in water

A distinct approach for the synthesis of α-aminonitriles has been discovered by three-component reaction of nitroarenes, aldehydes, and TMSCN using indium in dilute aqueous HCl at room temperature. The products were formed in high yields (86-96%) within a short period of time (5-20 min). This one-pot conversion consists of the following steps: (i) reduction of nitro compounds to amines, (ii) formation of imines from amines and aldehydes and (iii) addition of cyanide anion to the imines.     

Selective CC bond hydrogenation in unsaturated nitro compounds in the presence of the RhCl3-aliquat 336 catalyst system

The ion pair formed from aqueous rhodium trichloride and Aliquat 336 catalyzes the selective hydrogenation of olefinic CC bonds of a variety of unsaturated nitro compounds in a two liquid phase system at 30°C. Nitrobenzene gives, under these conditions, a mixture of aniline and nitrocyclohexane.     

Carbon-carbon bond-forming reactions of α-thioaryl carbonyl compounds for the synthesis of complex heterocyclic molecules

Strategies for the formation of carbon-carbon bonds from the α-thioaryl carbonyl products of substituted lactams are described. Although direct functionalization is possible, a two step process of oxidation and magnesium-sulfoxide exchange has proven optimal. The oxidation step results in the formation of two diastereomers that exhibit markedly different levels of stability toward elimination, which is rationalized on the basis of quantum mechanical calculations and X-ray crystallography. Treatment of the sulfoxide with i-PrMgCl results in the formation of a magnesium enolate that will undergo an intramolecular Michael addition reaction to form two new stereogenic centers. The relationship between the substitution patterns of the sulfoxide substrate and the efficiency of the magnesium exchange reaction are also described.     

“Matrix effects” in the activation of compounds with a system of conjugation in the inhibition of oxidative processes

Russian Chemical Bulletin -     

Synthesis of azamacrocyclic compounds by cyclocondensation of aliphatic α,ω-diamines with acetone

Cyclocondensation of 1,4-diaminobutane and 1,6-diaminohexane with acetone afforded the corresponding 18- and 22-membered trans-azamacrocyclic Curtis compounds in high yield, which contain two azomethine and amine nitrogen atoms. A complex mixture of the products formed containing less than 25% of 16-membered azamacrocyclic cis- and trans-isomers when reacting 1,3-diaminopropane with acetone.     

Synthesis of bicyclohomofarnesane compounds by the ozonization of “sclareol oxide”

Ozonolytic pathways for the selective transformation of sclareol oxide (I) with good yield into the bicyclohomofarnesane derivatives (II), (III), (V), and (VII) have been developed.Institute of Chemistry, Academy of Sciences of the Moldavian SSR, Kishinev. Translated from Khimiya Prirodnykh Soedinenii, No. 2, pp. 209–214, March–April, 1991.     

Synthesis of chiral organophosphorus compounds by the reaction of dibenzylphosphine oxide with α,β-unsaturated ketones of the terpene series

Dibenzylphosphine oxide readily reacts with ,-unsaturated terpene ketones in aprotic media to form both chiral phosphorus-containing heterocycles and acyclic chiral phosphine oxides.