The catalytic olefination reaction of aldehydes and ketones with CBr3CF3

The new approach of catalytic olefination reaction (COR) has been used to convert aromatic and aliphatic aldehydes and ketones to 2-bromo-3,3,3-trifluoroprop-1-enes by the treatment of corresponding hydrazones with CBr₃CF₃ under copper(I) catalysis conditions. The reaction proceeds stereoselectively, the target alkenes were obtained in good yields.     

A simple procedure for synthesis of 3H-quinazolin-4-one hydrazones under mild conditions

Condensation of 6-bromo- and 6,8-dibromo-2-hydrazino-3-phenyl-3H-quinazolin-4-ones with d-sugars in the presence of a catalytic quantity of glacial acetic acid gave the corresponding hydrazones in good yields. Acetylation of hydrazones with acetic anhydride in anhydrous pyridine gave the corresponding acetyl hydrazones in high yields. Also, other hydrazones were synthesized from condensation of 2-hydrazino-3H-quinazolin-4-ones with aromatic aldehydes in the presence of a catalytic quantity of piperidine.     

Reductive esterification of aromatic aldehydes using Zn/Ac2O/imidazole or Zn/Yb(OTf)3/(RCO)2O system

Benzaldehydes are reduced by metallic zinc in the presence of Ac₂O and imidazole, giving the corresponding benzyl acetates in good yields. Reductive esterification of aromatic aldehydes is also carried out via gem-diacetoxy compounds. Carbonyl compounds are readily converted to the gem-diacyloxy compounds in excellent yields on treatment with 2 molar amounts of acid anhydride and 10 mol% of Yb(OTf)₃ in MeCN at room temperature. Thus-formed diacyloxy compounds derived from aromatic aldehydes are reduced in situ by metallic zinc to afford the corresponding esters.     

Stable bis(1-bromo-2,2,2-trihaloalkoxy)phosphoranes from tetrafluoropropyl difluorophosphite

It was found that dibromo-2,2,3,3-tetrafluoropropoxydifluorophosphorane, obtained from 2,2,3,3-tetrafluoropropyl difluorophosphite and bromine, adds two moles of chloral or bromal with the formation of stable 2,2,3,3-tetrafluoropropoxybis(1-bromo-2,2,2-trihaloethoxy)difluorophosphoranes, the structure of which was confirmed by NMR data.Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No. 9, pp. 2118–2120, September, 1990.     

BF3·OEt2-catalyzed tandem Prins Friedel-Crafts reaction: a novel synthesis of sugar fused diarylhexahydro-2H-furo[3,2-b]pyrans

d-Glucose based homoallylic alcohol reacts smoothly with various aldehydes in the presence of arenes and a catalytic amount of BF₃·OEt₂ under mild conditions to afford a novel series of 5,7-diaryl-hexahydro-2H-furo[3,2-b]pyrans in good yields with high cis-selectivity.     

Selective 1,2-dihalogenation and oxy-1,1-dihalogenation of alkynes by N-halosuccinimides

1,2-Dihalogenation and oxy-1,1-dihalogenation of alkynes by N-halosuccinimides can be selectively realized through using different reaction conditions. α,β-Dihalo alkenes were obtained exclusively using THF as solvent without using any catalyst, while α,α-dihalo ketones were synthesized using a mixed solvent of THF and H₂O in the presence of FeCl₃·6H₂O. Terminal aromatic alkynes are smoothly transformed into α,α-dihalo ketones on water without a catalyst.     

Free radical (phenylsulfonyl)difluoromethylation of alkynes with PhSO2CF2I reagent: stereoselective preparation of PhSO2CF2- and CF2H-substituted alkenes

Stereoselective free radical (phenylsulfonyl)difluoromethylation of terminal alkynes with iododifluoromethyl phenyl sulfone (PhSO₂CF₂I) has been accomplished by using Et₃B/air as an initiator. The obtained PhSO₂CF₂-substituted vinyl iodides, which can be further subjected to Suzuki coupling and Sonogashira coupling reactions, are useful precursors for the preparation of many structurally diverse PhSO₂CF₂- and CF₂H-substituted alkenes.     

Copper (II)-catalyzed regio- and stereoselective addition of H/P(O)R2 to alkynes

Cu(acac)₂ is the new universal catalyst for β-E regio- and stereoselective syn-addition of the H–P(O)-bond of diphenylphosphine oxide, H-phosphinates, dialkylphosphites to various alkynes in the synthesis of P(O)-containing alkenes. Without additives and ligands Cu(II)-compounds showed better results than CuI or Ni(acac)₂. The catalytic system developed is tolerant to typical organic functional groups present in the alkynes and to the nature of different substituents in the H–P(O)-compounds.     

Facile synthesis of novel CF3-substituted ring-fused furo[2,3-c]pyrazoles through Rh2(OAc)4 catalyzed [3+2] cycloaddition of 4-diazo-1-phenyl-3-(trifluoromethyl)-1H-pyrazol-5(4H)-one with aromatic alkynes

The Rh₂(OAc)₄ catalyzed [3+2] cycloaddition of 4-diazo-1-phenyl-3-(trifluoromethyl)-1H-pyrazol-5(4H)-one with aromatic alkynes was studied, and this protocol can be efficiently applied to the synthesis of the novel CF₃-substituted ring-fused furo[2,3-c]pyrazoles.     

Homogeneous hydrogenation of alk-1-enes and alkynes catalyzed by the 1-[Ir(CO)(PhCN)(PPh3)]-7-C6H5-1,7-(σ-C2B10H10) complex

The complex [Ir(σ-carb)(CO)(PhCN)(PPh₃)], where carb = -7-C₆H₅-1,2C₂B₁₀H₁₀, was found to be an effective catalyst for homogeneous hydrogenation of terminal olefins and acetylenes at room temperature and atmospheric or subatmospheric hydrogen pressure. Internal olefins are not hydrogenated, but simple alk-1-enes are readily converted into the corresponding alkanes. Isomerization of the double bond catalyzed by the metal complex occurs at very small extent. Catalytic hydrogenation of olefins having carboxylate substituents on the unsaturated carbon atoms is prevented by the formation of thermally stable chelate hydridoalkyl complexes of the type I$\text{(H)}$(σ-CHRCHR′C(O)OR″) (σ-carb)(CO)(PPh₃)]. Acetylenes are hydrogenated to alkenes. The alk-1-enes formed in the hydrogenation of the alkynes HCCR in turn undergo the more slow reactions either of hydrogenation to alkanes or isomerization to internal olefins which cannot be further hydrogenated. Hydrogenation of alkynes of the type RCCR′ is stereospecifically cis, yielding cis- olefins. Catalyzed cis → trans isomerization reaction of these internal olefins occurs only to a negligeable extent.     

Novel efficient synthesis of β-fluoro-β-(trifluoromethyl)styrenes

CF₃CFBr₂ was employed in catalytic olefination reactions of aromatic aldehydes. In situ prepared hydrazones of aldehydes were transformed to β-fluoro-β-(trifluoromethyl)styrenes by reaction with CF₃CFBr₂ under CuCl catalysis. Based on this reaction, a novel stereoselective approach towards β-fluoro-β-(trifluoromethyl)styrenes was elaborated. Nucleophilic vinylic substitution of fluorine by secondary amines, thiolates and alkoxides in β-fluoro-β-(trifluoromethyl)styrenes was also tested.     

AIPO4 Supported Zinc Borohydride as a Novel Reagent for the Hydration of Aromatic Alkenes and Alkynes

Hydration of aromatic alkenes (styrene, α-methylstyrene and E-stilbene) and alkynes (phenyl and diphenylacetylene) has been achieved by the reaction of the corresponding alkenes or alkynes on zinc borohydride combined with AIPO₄ in DME. Except in the case of α-methylstyrene, Zn(BH₄)₂/AIPO₄ provides a more efficient and selective catalytic system than the combination with SiO₂ or Al₂O₃.     

Synthesis of 2′-hydrazine oligonucleotides and their efficient conjugation with aldehydes and 1,3-diketones

Oligodeoxyribonucleotides that contain a novel nucleoside, 2′-O-(2-hydrazinoethyl)uridine, were synthesised by NaBH₃CN reduction of hydrazones formed from 2′-O-(2-oxoethyl)oligonucleotides with FmocNHNH₂, followed by concd aq NH₃ deprotection. The 2′-hydrazine oligonucleotides obtained were then used to synthesise a number of conjugates with aldehydes via hydrazone formation and with1,3-diketones via pyrazole formation. The method was shown to be applicable for the preparation of oligonucleotide-peptide conjugates.     

Recent advances in the synthetic and mechanistic aspects of the ruthenium-catalyzed carbon-heteroatom bond forming reactions of alkenes and alkynes

The group’s recent advances in catalytic carbon-to-heteroatom bond forming reactions of alkenes and alkynes are described. For the C-O bond formation reaction, a well-defined bifunctional ruthenium-amido catalyst has been successfully employed for the conjugate addition of alcohols to acrylic compounds. The ruthenium-hydride complex (PCy₃)₂(CO)RuHCl was found to be a highly effective catalyst for the regioselective alkyne-to-carboxylic acid coupling reaction in yielding synthetically useful enol ester products. Cationic ruthenium-hydride catalyst generated in-situ from (PCy₃)₂(CO)RuHCl/HBF₄·OEt₂ was successfully utilized for both the hydroamination and related C-N bond forming reactions of alkenes. For the C-Si bond formation reaction, regio- and stereoselective dehydrosilylation of alkenes and hydrosilylation of alkynes have been developed by using a well-defined ruthenium-hydride catalyst. Scope and mechanistic aspects of these carbon-to-heteroatom bond forming reactions are discussed.     

Synthesis of 1,2-disubstitued benzimidazoles using SiO2/ZnCl2

A general and easy method for the synthesis of several 1,2-disubstituted benzimidazoles using SiO₂/ZnCl₂ and solvent-free conditions is described. This efficient and improved method furnishes selectively and in good yields the corresponding 1,2-bis(organyl)-benzimidazoles starting from o-phenylenediamine and aromatic or aliphatic aldehydes. The catalytic system was re-used up three times and the use of focused microwaves accelerates the reaction.     

Bi2O3-catalyzed oxidation of aldehydes with t-BuOOH

A variety of aromatic, aliphatic and conjugated aldehydes were transformed to the corresponding carboxylic acids with 70% t-BuOOH solution (water) in the presence of catalytic amounts of Bi₂O₃. This method possesses a wide range of capabilities, does not involve cumbersome work-up, exhibits chemoselectivity and proceeds under mild conditions. The resulting products are obtained in good yields within reasonable time. The overall method is green.     

Ti(NMe2)4-catalyzed Markovnikov hydroamination of alkynes in the presence of N-heterocyclic carbenes and LiN(SiMe3)2

Intermolecular hydroamination of alkynes catalyzed by Ti(NMe₂)₄ was much improved with N-heterocyclic carbenes and LiN(SiMe₃)₂, by which high Markovnikov selectivity was attained for the coupling of nearly all alkynes and amines.     

Arylation of lawsone through BF3-mediated coupling of its phenyliodonium ylide with activated arenes and aromatic aldehydes

Phenyliodonium ylide of lawsone, activated by BF₃·Et₂O, reacts with electron-rich arenes to afford the corresponding 2-aryl-3-hydroxy-1,4-naphthoquinones, in a coupling reaction without metal catalysts. The same type of products, in greater variety and higher yields, are obtained from the reaction of the BF₃·Et₂O-activated ylide with aromatic aldehydes in a synthetically and mechanistically interesting deformylation reaction.     

Electrophilic Bromination of Alkenes,Alkynes, and Aromatic Amines with Iodic Acid/Potassium Bromide Under Mild Conditions

Bromination of alkenes, alkynes, and aromatic amines has efficiently been carried out at room temperature in short reaction times using HIO₃/KBr in CH₂Cl₂/H₂O (1:1) to prepare corresponding brominated compounds in excellent yields.     

Synthesis of 3-substituted benzo[g]isoquinoline-5,10-diones: a convenient one-pot Sonogashira coupling/iminoannulation procedure

A series of 3-substituted 5,10-dimethoxybenzo[g]isoquinolines were prepared by coupling of terminal alkynes with the tert-butylimine of 3-bromo-1,4-dimethoxy-2-naphthaldehyde in the presence of a Pd-catalyst and subsequent Cu-catalyzed cyclization of the intermediate 3-alkynyl-2-naphthylcarbaldehyde. A CAN-mediated oxidative demethylation yielded the corresponding 2-azaanthraquinones in excellent yields. Since this methodology proved to be limited to alkynes bearing aromatic groups, an alternative and more general Pd-catalyzed coupling procedure was developed, starting from 3-bromo-1,4-dimethoxy-2-naphthaldehyde. For more acidic terminal alkynes, like phenylacetylene, a combination of Pd(OAc)₂/P(t-Bu)₃/CuI (2/6/1) with potassium carbonate in DMF gave a complete conversion within 24 h. For less acidic acetylenes, 2 equiv of alkyne and caesium carbonate as a base were required in order to obtain complete conversion of the starting material within 24 h. These altered Sonogashira conditions also allowed the isolation of a benzo[f]indenone as an interesting side product in case Bu₄NCl was added to the reaction mixture. The 3-alkynyl-1,4-dimethoxy-2-naphthaldehyde acquired after completion of the Pd-catalyzed coupling could be cyclized by adding a solution of ethanolic ammonia and an extra equivalent of potassium carbonate to the reaction mixture. As such, this consecutive one-pot coupling/iminoannulation procedure was a convenient alternative to the Larock isoquinoline procedure, enabling the isolation of a series of 3-substituted 5,10-dimethoxybenzo[g]isoquinolines.