Copper acetylide catalysis

In volume terms, the most important ethynylation product is butynediol. It is prepared with copper acetylide catalysis [5] from aqueous formaldehyde and acetylene (eq. (1)). Heterogeneous copper catalysts, on support materials, are most commonly used for this reaction. 

Terminal alkynes react with propargylic carbonates at room temperature to afford the alka-l, 2-dien-4-yne 14 (allenylalkyne) in good yield with catalysis by Pd(0) and Cul[5], The reaction can be explained by the transmetallation of the (7-allenylpailadium methoxide 4 with copper acetylides to form the allenyKalk-ynyl)palladium 13, which undergoes reductive elimination to form the allenyl alkyne 14. In addition to propargylic carbonates, propargylic chlorides and acetates (in the presence of ZnCb) also react with terminal alkynes to afford allenylalkynes[6], Allenylalkynes are prepared by the reaction of the alkynyl-oxiranes 15 with zinc acetylides[7]. 

Transition-Metal Catalyzed Cyclizations. o-Halogenated anilines and anilides can serve as indole precursors in a group of reactions which are typically catalyzed by transition metals. Several catalysts have been developed which convert o-haloanilines or anilides to indoles by reaction with acetylenes. An early procedure involved coupling to a copper acetylide with 0-iodoaniline. A more versatile procedure involves palladium catalysis of the reaction of an 0-bromo- or 0-trifluoromethylsulfonyloxyanilide with a trialkylstannylalkyne. The reaction is conducted in two stages, first with a Pd(0) and then a Pd(II) catalyst (29). 

Other unsaturated substrates arylated by various diaryl iodonium salts included butenone, acrylic acid, methyl acrylate and acrylonitrile [46]. Allyl alcohols with diaryliodonium bromides and palladium catalysis were arylated with concomitant oxidation for example, from oc-methylallyl alcohol, aldehydes of the general formula ArCH2CH(Me)CHO were formed [47]. Copper acetylide [48] and phenyl-acetylene [49] were also arylated, with palladium catalysis. 

The conversion of a carbon-thallium bond into a carbon-carbon bond has been performed directly only in a relatively limited number of cases formation of aiylcyanides, reaction with nitroalkane salts as well as the reaction with copper acetylides. Other carbon-carbon bond formation reactions have been reported with a carbon-thallium substrate. However, they all involve palladium catalysis, and this is beyond the scope of this book. 147... 

Ring closure of ortfto-aminoaryl-alkynyl-carbinols, readily available by acetylide addition to an aryl-ketone or -aldehyde, can be achieved with copper or palladium catalysis. Comparable ort/io-nitroaryl-carbinols undergo nitro group reduction and ring closure simply by treatment with a metal/acid combination. ... 

Several new methods for the preparation of 1-haloalkynes have been described. High yields of bromo compounds, e.g. 28, are obtained by treatment of alkynes with triphenylphosphine/carbon tetrabromide, or with a concentrated aqueous solution of potassium hypobromite and potassium hydroxide (equation 1). 1-Iodoalkynes are produced from terminal alkynes and bis(pyridine)iodine(I) tetrafluoroborate in methanol in the presence of sodium methoxide (equation 2) or from alkynes with a mixture of iodine, potassium carbonate, copper(I) iodide and tetrabutylammonium chloride under phase-transfer catalysis. Lithium acetylides 29 (R = Ph, t-Bu, HOCH2 etc.) react with zinc iodide and bis(trimethylsilyl) peroxide to yield 1-iodoalkynes. The method has been... 

In contrast, Cu(I) catalysis makes possible the efficient synthesis of 3,5-disubsti-tuted isoxazoles 57 from aromatic or aliphatic aldehydes and alkynes. Stable nitrile oxides can be isolated and subsequently submitted to the reaction [21] in isolated form and submitted to the reaction in one-pot, three-step process [131]. Here, nitrile oxide intermediates 56 are generated in situ via the corresponding aldoxime and halogenation/deprotonation by Chloramine-T [132]. Capture of the intermediate nitrile oxide by copper(I) acetylides occurs presumably before dimerization. In this case, the Cu catalyst was obtained from copper metal and copper(II) sulfate, and the products were isolated by simple filtration or aqueous work-up. Trace amounts of toluenesulfonamide and unreacted acetylene are easily removed by recrystallization or by passing the product through a short plug of silica gel. 

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