Direct and selective arylation of tertiary silanes with rhodium catalyst

We have developed a convenient and efficient approach to the arylation of tertiary silanes under mild conditions. A variety of arylsilanes were synthesized in a one-step process with good to excellent yields in the presence of a rhodium catalyst with a base. The reaction was highly solvent dependent, and amides were the most effective of the various solvents used. This common catalyst system is highly tolerant of the various sensitive functional groups on the substrates, which might be difficult to extract by other methods. The rhodium-promoted silylation of aryl halides with electron-donating groups occurred more efficiently than the silylation of aryl halides substituted with electron-withdrawing groups. Heteroaromatic halides were also found to be readily silylated with tertiary silanes. The successful application of this reaction to the synthesis of a TAC-101 analogue, which is a trialkylsilyl-containing synthetic retinoid benzoic acid derivative with selective binding affinity for retinoic acid receptor-alpha, is also described.     

Bi(III) halides as efficient catalysts for the O-acylative cleavage of tetrahydrofurans: an expeditious entry to tetralins

The mild (DCM/20 °C), quantitative, regioselective, O-acylative cleavage of tetrahydrofurans using organic acid halides with catalytic Bi(III) halides is reported. X-ray crystallography is used to rationalise the failure of the reaction in the case of certain crowded acid chlorides, and a useful aspect of chemoselectivity is revealed. The synthetic potential of this reaction is illustrated with a highly efficient O-acylative cleavage/intramolecular alkylation approach to tetralins.     

Visible‐Light‐Promoted Nickel‐ and Organic‐Dye‐Cocatalyzed Formylation Reaction of Aryl Halides and Triflates and Vinyl Bromides with Diethoxyacetic Acid as a Formyl Equivalent

A simple formylation reaction of aryl halides, aryl triflates, and vinyl bromides under synergistic nickel‐ and organic‐dye‐mediated photoredox catalysis is reported. Distinct from widely used palladium‐catalyzed formylation processes, this reaction proceeds by a two‐step mechanistic sequence involving initial in situ generation of the diethoxymethyl radical from diethoxyacetic acid by a 4CzIPN‐mediated photoredox reaction. The formyl‐radical equivalent then undergoes nickel‐catalyzed substitution reactions with aryl halides and triflates and vinyl bromides to form the corresponding aldehyde products. Significantly, besides aryl bromides, less reactive aryl chlorides and triflates and vinyl halides serve as effective substrates for this process. Since the mild conditions involved in this reaction tolerate a plethora of functional groups, the process can be applied to the efficient preparation of diverse aromatic aldehydes.     

Nitromethane with IBX/TBAF as a nitrosating agent: synthesis of nitrosamines from secondary or tertiary amines under mild conditions

Aliphatic or aromatic N,N-disubstituted nitrosamine was generated in fair to excellent yield from the reaction of a secondary or tertiary amine with o-iodoxybenzoic acid (IBX) or o-iodosylbenzoic acid (IBA)/R(4)NX (X = halide) and nitromethane. The product yield was strongly influenced by both the halide of R(4)NX and iodanes. IBX gave a higher yield than IBA, while the halides follow F(-) > Cl(-) > Br(-) ～ I(-). Nitrous acid formed in situ from nitromethane and IBX (or IBA)/halides is likely responsible for the observed reaction.     

Cross-coupling reaction of alpha-chloroketones and organotin enolates catalyzed by zinc halides for synthesis of gamma-diketones

The reaction of tin enolates 1 with alpha-chloro- or bromoketones 2 gave gamma-diketones (1,4-diketones) 3 catalyzed by zinc halides. In contrast to the exclusive formation of 1,4-diketones 3 under catalytic conditions, uncatalyzed reaction of 1 with 2 gave aldol-type products 4 through carbonyl attack. NMR study indicates that the catalyzed reaction includes precondensation between tin enolates and alpha-haloketones providing an aldol-type species and their rearrangement of the oxoalkyl group with leaving halogen to produce 1,4-diketones. The catalyst, zinc halides, plays an important role in each step. The carbonyl attack for precondensation is accelerated by the catalyst as Lewis acid and the intermediate zincate promotes the rearrangement by releasing oxygen and bonding with halogen. Various types of tin enolates and alpha-chloro- and bromoketones were applied to the zinc-catalyzed cross-coupling. On the other hand, the allylic halides, which have no carbonyl moiety, were inert to the zinc-catalyzed coupling with tin enolates. The copper halides showed high catalytic activity for the coupling between tin enolates 1 and organic halides 7 to give gamma,delta-unsaturated ketones 8 and/or 9. The reaction with even chlorides proceeded effectively by the catalytic system.     

An easy entry into 2-halo-3-aryl-4(3H)-quinazoliniminium halides from heteroenyne-allenes

An efficient three-step synthesis of 2-halo-3-aryl-4(3H)-quinazoliniminium halides from commercially available materials is described. Upon reaction with hydrogen halides, generated in situ from a Lewis acid (MX) and trace water, a variety of easily accessible heteroenyne-allenes underwent facile intramolecular cyclization to afford the title compounds in good yields. The method is highly versatile and provides a general way to construct quinazoliniminium ring systems with a variety of different substitutions.     

Immobilization of HX：[Hmim]X as Halogenating Agent, Recyclable Catalyst and Medium for Conversion of Alcohols to Alkyl Halides

HX is immobilized by reaction of halogen acid with methylimidazole, and the formed ionic liquid [Hmim]X was used as halogenating agent, catalyst as well as medium for conversion of alcohols to alkyl halides. Excellent yields were obtained. The halides produced could be easily separated from the reaction mixture via simple decantation, and the ionic liquid [Hmim]X could be regenerated conveniently by adding equivalent of halogen acids followed by removal of water.     

N-acylazinium salts: a new source of iminium ions for Ugi-type processes

A multicomponent reaction involving the interaction of azines (quinolines, isoquinolines, and phenanthridine) with activating agents (chloroformates, acid halides, and sulfonyl halides), isocyanides, and water is described. The products of this process, alpha-carbamoylated-1,2-dihydroazines, are the result of the addition of the isocyanide partner to the N-acylazinium salt formed in situ. This represents a new source of iminium ion equivalents for Ugi-type reactions.     

The Behavior of Acid Halides Toward Lewis Acids and Lewis Bases

Reactions of some typical acid halides of carbonic and trithiocarbonic acids and of orthophosphoric and sulfuric acids with Lewis acids and Lewis bases are compared. Acylium, perfluoroacylium, thioacylium, and even sulfonylium ions are obtainable with Lewis acids. It is possible by conductivity measurements and by electronic and above all IR spectroscopic investigations to determine whether the 1:1 adducts of acid halides and Lewis compounds are acylium or sulfonylium salts or donor-acceptor complexes. In the reaction with Lewis bases, the halogen atom in the acid halide is replaced by the electron donor, generally with formation of nonpolar molecular compounds or complexes.     

Phenyl trifluorovinyl sulfide: a radical acceptor for preparation of gem-difluoromethylene compounds

Phenyl trifluorovinyl sulfide was prepared from the reaction of trifluorovinyllithium and S-phenyl benzenethiosulfonate. The fluorinated olefin showed reactivity with alkyl radicals generated from halogen-abstraction from alkyl halides. Reactions with alkyl halides required tris(trimethylsilyl)silane as a chain transfer reagent to improve selectivity of the products. Initiation of radical reaction was effected by thermal decomposition of AIBN. Oxidation of the thioether products gave the corresponding sulfoxides, which were successively converted into α,α-difluoroalkanecarboxylic acid thiol esters by Pummerer reaction.     

Mechanistic and synthetic aspects of the reaction of alkyl esters of phosphorus with trimethylstannyl halides

The reaction of trimethylstannyl halides with trialkyl phosphates has been studied. The results are interpreted in terms of a mechanism involving a trimethylstannyloxyphosphonium salt intermediate. The much lower reactivity of the stannyl halides compared with their silicon analogs is explained by the lower ionization of the stannyl halide phosphate complexes and the unfavourable direction of the decomposition of the phosphonium salt intermediate. The reaction may be useful in synthesis of phosphates containing only one O-stannyl group, which can be used in generation of the acid function or replaced in reactions with compounds containing active halogen.     

Convenient synthesis of 3-vinyl and 3-styryl coumarins

A variety of 2-hydroxy aldehydes on reaction with 3-butenoic acid afford in a one-pot reaction the corresponding 3-vinylcoumarins. As expected, extension of the delocalized π-electron system accomplished by Heck coupling reactions with aryl halides results in an increased fluorescence of the compounds whose applicability is yet to be established.     

A new regiospecific synthesis of aryl ketones from palladocycles

Aromatic palladocycles undergo facile reaction with acid halides to reglospecifically provide aryl ketones In high yield.     

Nickel-Catalyzed Preparations of Functionalized Organozincs

The reaction of primary alkyl bromides or chlorides with diethylzinc in the presence of Ni(acac)(2) (5 mol %) furnishes the corresponding alkylzinc halides (X = Br, Cl) via a halogen-zinc exchange reaction. The treatment of terminal alkenes with diethylzinc (neat, 25-60 degrees C) in the presence of Ni(acac)(2) as a catalyst (1-5 mol %) and 1,5-cyclooctadiene (COD) affords the corresponding dialkylzincs via a hydrozincation reaction. Whereas the conversion for simple alkenes bearing a remote functionality reaches 40 to 63%, the hydrozincation of allylic, homoallylic alcohols and allylic amines proceeds very efficiently (85-95% conversion). All the zinc organometallics obtained react with various electrophiles (allylic halides, enones, acid chlorides, alkynyl halides, ethyl propiolate) after transmetalation with CuCN.2LiCl. In the presence of the chiral catalyst 12, the dialkylzincs prepared add to aldehydes with high enantioselectivity.     

Allylic halogenation of unsaturated amino acids

A range of dehydro amino acid derivatives has been prepared and subjected to halogenation using either molecular bromine or chlorine, or NBS. Allylic halogenation of the unsaturated amino acid side chains occurs through radical bromination with NBS. The procedure is complementary to treatment with chlorine, which also affords allyl halides. This latter and unusual reaction is shown through a deuterium labelling study to proceed via an ionic mechanism. The choice of NBS or chlorine for allyl halide synthesis is shown to depend on the potential to avoid competing reactions, such as halolactonization of leucine derivatives with chlorine, and hydrogen abstraction and bromine incorporation at multiple sites on treatment of isoleucine derivatives with NBS. The synthetic utility of the allyl halides prepared in this study is indicated through the synthesis of a cyclopropyl amino acid derivative and the extension of the carbon skeleton of an amino acid side chain.     

Palladium-Catalyzed Chlorocarbonylation of Aryl (Pseudo)Halides Through In Situ Generation of Carbon Monoxide

An efficient palladium-catalyzed chlorocarbonylation of aryl (pseudo)halides that gives access to a wide range of carboxylic acid derivatives has been developed. The use of butyryl chloride as a combined CO and Cl source eludes the need for toxic, gaseous carbon monoxide, thus facilitating the synthesis of high-value products from readily available aryl (pseudo)halides. The combination of palladium(0), Xantphos, and an amine base is essential to promote this broadly applicable catalytic reaction. Overall, this reaction provides access to a great variety of carbonyl-containing products through in situ transformation of the generated aroyl chloride. Combined experimental and computational studies support a reaction mechanism involving in situ generation of CO.     

Synthesis of alpha-amino acid derivatives and amines via activation of simple alkyl halides by zinc in water

A method for the synthesis of alpha-amino acid derivatives and amines is developed via a zinc-mediated conjugate addition reaction of alkyl halides to alpha-phthalimidoacrylate derivatives and nucleophilic addition to imines in the presence of NH4Cl in water. No reaction was observed in the absence of water.     

A New Approach to P-C Bond Formation by Using Tri-Methylsilyl Phosphites

Abstract

The in situ silylation of phosphorous acid diesters to phosphorous acid triesters by hexamethyldisilazane and trimethylsilyl halides under conditions of Michaelis-Arbuzov reaction was found as an efficient and facile reaction principle for P-C bond formation.

In general the method can be applied also to Michaelis-Arbuzov reactions of phosphonous and hypophosphorous acid esters, to Tavs reaction of phosphorous and phosphonous acid esters as well as to photochemical conversions of arylhalides with trimethylsilyl phosphites. In any case described the observed yield is nearly quantitative.     

Pyridinium Halides and Their Mixtures as Inhibitors of Steel Corrosion in Sulfuric Acid Solutions

Mixtures of 1-acylmethylpyridinium halides with equimolar amounts of pyridinium halides were prepared by the Ortoleva-King reaction. The inhibiting effect of various pyridinium halides and their mixtures on corrosion of steel in sulfuric acid solutions was studied.__________Translated from Zhurnal Prikladnoi Khimii, Vol. 78, No. 3, 2005, pp. 517–519.Original Russian Text Copyright © 2005 by Yurchenko, Ivashchenko, Pilipenko, Pogrebova.     

Chemospecific and ligand free CuI catalysed heterogeneous N-arylation of amines with diheteroaryl halides at room temperature

A ligand free, copper-catalyzed N-arylation reaction of amines with diheteroaryl halides in heterogeneous medium at room temperature has been developed. The protocol is very effective for low boiling amines and useful for amines available in aqueous solution. The reaction gives chemospecific arylation of amines with diheteroaryl halides in the mixture monoheteroaryl halides, diheteroaryl halides and carbocyclic aryl halides. The reaction is also chemospecific with respect to arylation of aliphatic amines. Monoarylated piperazines were also synthesized at room temperature following this protocol.