Direct copper-catalyzed

The direct, copper catalyzed reaction of methyl chlorid with silicon, the Direct Process , is the most important reaction for the production of methylsilicon intermediates. A similar reaction with hydrogen chloride yields trichlorosilane, which in turn is the basis for trifiinctional intermediates and also for polycrystalline silicon, the raw material for the semiconductor industry. This Direct Process has been practiced for fifty years and much progress has been made by many towards understanding and optimizing the process, but much still remains to be learned about this complex series of heterogeneous reactions. 

A one-pot, copper-catalyzed formation of fully decorated triazoles was recently demonstrated by Ackermann. In the first step, a copper-catalyzed click reaction produces triazoles from alkynes and azides. In the second step, a direct, copper-catalyzed... 

Direct copper-catalyzed coupling of sulfonamides and isocyanates was achieved with the highest yield when CuCl (5 mol%) catalyst was used in LAG (nitromethane) milling (Scheme 3.54). Within 2h of grinding, sulfonylureas 211 were produced in high yield, and workup included ball milling for lOmin with water and Na2H2EDTA to remove catalyst (Table 3.25). 

The direct copper-catalyzed iodosyl-mediated nitrogen transfer to olefins compares with the parent rhodium-catalyzed process that is made possible by the combination of iodosylbenzene diacetate, magnesium oxide, and sulfamates. Other recent promising nitrene transfer methods involve the bromine-catalyzed aziridination of olefins using chloramine-T and the direct electrochemical aziridination with TV aminophthalimide. ... 

Scheme 76 Quinoline-directed copper-catalyzed oxidation of arenes.

A highly practical ligand-free copper-catalyzed systan for the intra-molecu-lar direct C—H arylation of electron-rich azaheterocycles has been reported by Dominquez et al. " Complex hetero-fused compounds were synthesized under mild conditions, which did not have to be anhydrous, thus simplifying the protocol. A highlight was the tolerance of the reaction conditions to additional halogens this, therefore, allows for further synthetic transformations. These are summarized in Table 7.4. The authors cite entries 3 and 4 to be the first direct copper-catalyzed C—H functionalizations of both 9//-purine and 4-azabenzimidazoles. These compounds are eminently important for their cardiovascular properties and use in the treatment of viral diseases such as AIDS and HIV. 

Seko and coworkers have discovered a convenient copper-catalyzed direct IS v/ith O-alkylhydtoxylamines fEq 9 50 ... 

Copper-catalyzed systems have been developed that reduce ketones directly to silyl ethers. The reactions involve chiral biphenyl diphosphine type ligands and silane or siloxane hydride donors.187... 

Addition of carbethoxynitrenes to olefinic double bonds occurs readily. Addition of both the singlet and the triplet species can take place, the former stereospecifically, the latter not 49>. Additions of sulphonyl nitrenes to double bonds have not been demonstrated except in two instances in which metals were present. The reason is that either addition of the starting sulphonyl azide to the double bond occurs to give a triazoline that loses nitrogen and yields the same aziridine as would have been obtained by the direct addition of the nitrene to the olefin, or the double bond participates in the nitrogen elimination and a free nitrene is never involved 68>. The copper-catalyzed decomposition of benzenesulphonyl azide in cyclohexene did give the aziridine 56 (15%), which was formulated as an attack by the sulphonyl nitrene-copper complex on the double bond 24>. 

M. T. Bilodeau, Ph.D. Thesis I. Studies on the Direct Formation of Chlorotitanium Enolates. II. The Development of the Copper-Catalyzed Aziridination Reaction, Harvard University, Cambridge, MA, 1993. 

A systematic investigation of the copper-catalyzed reaction between 2-bromobenzoic acid and the anions of 1,3-dicarbonyl compounds has established the optimum conditions for the direct arylation of the /3-dicarbonyl moiety (75T2607). The use of sodium hydride as the base and copper(I) bromide as catalyst is recommended. The absence of a protic solvent ensures that competitive attack on the bromobenzoic acid by a solvent-derived base leading to a salicylic acid is eliminated. For larger scale reactions the addition of toluene offers some practical advantages. 

Although no direct oxygen transfer reactions from well-characterized rhodium-hydroperoxo or -alkylperoxo complexes to alkenes have yet been reported, these species are probably involved in the rhodium-copper catalyzed ketonization of terminal alkenes by 02, as previously shown in Section 61.3.2.1.3. Rhodium trichloride has been used to catalyze the ketonization of terminal alkenes by H202 or TBHP in alcoholic solvents, but these reactions occur less efficiently than with the Rh/Cu/02 system.207... 

The reaction of carbenoids with aromatic systems was first reported by Buchner and coworkers in the 1890s.6 The reaction offers a direct entry to cycloheptatrienes and has been used to synthesize tropones, tropolones and azulenes.6 Neither the thermal nor copper-catalyzed reactions, however, proceed in good yield. The problems associated with these transformations were clearly demonstrated in a recent reexamination of die thermal decomposition of ethyl diazoacetate in excess anisole (137).129 A careful analysis of the reaction mixture revealed the presence of seven components (138-144) in 34% overall yield (Scheme 29). The cycloheptatrienes (138M142) were considered to be formed by cyclopropanation followed by electrocyclic ring opening of the resulting norcaradienes. A mixture of products arose because the cyclopropanation was not regioselective and, also, the initially formed cycloheptatrienes were labile under the reaction conditions. 

The reaction has been modified to a more regioselective, copper-catalyzed stepwise process by the Sharpless group, which is no longer a classic Huisgen Cycloaddition. Another approach prefers the use of a directing electron withdrawing group, which is removable later ... 

Some interesting intramolecular variants have been reported. For example, homoallylic alcohols (e.g. 139) can be treated with sulfamoyl chloride to form the corresponding sulfamates (140), which then engage in a direct intramolecular copper-catalyzed aziridination mediated by iodosylbenzene <02OL2481>. A carbamate tether is also effective in delivering the nitrene center to the olefin, as is the case with the cyclohexenyl derivative 142, which spontaneously cyclizes in the presence of iodosylbenzene <02OL2137>. The acetoxy-aminoquinazolinone 144 is converted to the lactone 145 via intramolecular aziridination upon treatment with lead tetraacetate and hexamethyldisilazane (HMDS) <02TL2083>. 

Direct palladium-catalyzed GG bond formation can be achieved between A -methy 1 imidazo 1 e and an aryl halide with selectivity for the more electron-rich C(5) position (Scheme 162) if C(5) is already substituted, then C(2) is preferred. iV-Methylbenzimidazole can be similarly arylated by various aryl iodides at the 2-position when catalyzed by copper(I) iodide to give excellent yields <1998BCJ467>. Rhodium can also catalyze direct C(2) arylation of N-alkyl benzimidazoles <20040L35>. 

Zeitler K (2006) Stereoselective synthesis of (E)-afi—unsaturated esters via carbene-catalyzed redox esterification. Qrg Lett 8 637-640 Zeitler K, Mager I (2007) An efficient and versatile approach for the immobilization of carbene precursors via copper-catalyzed [3+2]-cycloaddition and their catalytic apphcation. Adv Synth Cat 349 1851-1857 Zhao GL, Cordova A (2007) A one-pot combination of amine and heterocyclic carbene catalysis direct asymmetric synthesis of fi-hydroxy and fS-malonale esters from a,fS-unsaturated aldehydes. Tetrahedron Lett 48 5976-5980 Zhou ZZ, Ji FQ, Cao M, Yang GF (2006) An efficient intramolecular Stetter reaction in room temperature ionic liquids promoted by microwave irradiation. Adv Synth Cat 348 1826-1830... 

The synthesis of symmetrically and unsymmetrically substituted J ,J -diarylimidazolin-2-ones by copper-catalyzed arylamidation under microwave-assisted and conventional conditions was studied <07S1403>. Palladium-catalyzed direct functionalization of imidazolinone with aryl halides has been reported <07JA7768>. 

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