Acetylenes, cleavage

Pd(C5Ph5- / )]2( <-C2Ph2), is prepared in moderate yield from the novel acetylene-cleavage reaction between palladium diacetate and diphenylacetylene in methanol. 

Tetracyanoethylene oxide [3189-43-3] (8), oxiranetetracarbonitnle, is the most notable member of the class of oxacyanocarbons (57). It is made by treating TCNE with hydrogen peroxide in acetonitrile. In reactions unprecedented for olefin oxides, it adds to olefins to form 2,2,5,5-tetracyanotetrahydrofuran [3041-31-4] in the case of ethylene, acetylenes, and aromatic hydrocarbons via cleavage of the ring C—C bond. The benzene adduct (9) is 3t ,7t -dihydro-l,l,3,3-phthalantetracarbonitrile [3041-36-9], C22HgN O. 

Cleavage of epoxy ketones to an acetylene and a cait>onyl compound via suHonylhydrazone. 

Me3SiI, CH2CI2, 25°, 15 min, 85-95% yield.Under these cleavage conditions i,3-dithiolanes, alkyl and trimethylsilyl enol ethers, and enol acetates are stable. 1,3-Dioxolanes give complex mixtures. Alcohols, epoxides, trityl, r-butyl, and benzyl ethers and esters are reactive. Most other ethers and esters, amines, amides, ketones, olefins, acetylenes, and halides are expected to be stable. 

Nickel peroxide is a solid, insoluble oxidant prepared by reaction of nickel (II) salts with hypochlorite or ozone in aqueous alkaline solution. This reagent when used in nonpolar medium is similar to, but more reactive than, activated manganese dioxide in selectively oxidizing allylic or acetylenic alcohols. It also reacts rapidly with amines, phenols, hydrazones and sulfides so that selective oxidation of allylic alcohols in the presence of these functionalities may not be possible. In basic media the oxidizing power of nickel peroxide is increased and saturated primary alcohols can be oxidized directly to carboxylic acids. In the presence of ammonia at —20°, primary allylic alcohols give amides while at elevated temperatures nitriles are formed. At elevated temperatures efficient cleavage of a-glycols, a-ketols... 

Electrochemical addition of perfluorobutyl iodide to 2-methyl-3-butyn-2-ol followed by basic dehydroiodmation and thermal cleavage gives perfluorobutyl-acetylene in an overall yield of 83% [34] (equation 26)... 

Later, the method of cleavage of the tertiary acetylenic alcohols in boiling benzene or toluene in the presence of NaOH or KOH was reported (88M253 2001UP1). 

Retrosynthetic cleavage of the indicated bond in 9 provides acetylenic aldehyde 23 as a potential precursor. It was anticipated that the action of a suitable base on 23 would result in the formation of an acetylide anion, a competent carbon nucleophile that could... 

Data are also available with a-acetylenic aliphatic sulphones, which involve only two steps i.e., saturation of the triple bond without subsequent cleavage of the Caliphalic—S bond, since it is not reactive. However, the introduction of an aromatic ring to the S02 group does not lead, contrary to what is observed with enones, to a potential shift toward less reducing potential values. Thus, the aromatic moiety introduced apparently does not bring any additional conjugation effect but even seems to decrease the activation of the unsaturated bond, as shown by data in Tables 6 and 7 where most of the potentials refer to the same saturated calomel electrode under similar experimental conditions. 

A very detailed comparison for every single step of the whole sequence (linking of a pyrazinone to the solid support, Diels-Alder reaction with acetylenic dienophile and cleavage of a formed pyridinone from the resin) was made between microwave irradiation and conventional heating conditions [115]. 

As corroborated by deuterium labeling studies, the catalytic mechanism likely involves oxidative dimerization of acetylene to form a rhodacyclopen-tadiene [113] followed by carbonyl insertion [114,115]. Protonolytic cleavage of the resulting oxarhodacycloheptadiene by the Bronsted acid co-catalyst gives rise to a vinyl rhodium carboxylate, which upon hydrogenolysis through a six-centered transition structure and subsequent C - H reductive elimina-... 

The formation of 2H-pyrroles (21) and a pyrrole derivative (22) from the reaction of 3-phenyl-2//-azirines and acetylenic esters in the presence of molybdenum hexacarbonyl is intriguing mechanistically (Schemes 24, 25).53 Carbon-nitrogen bond cleavage must occur perhaps via a molybdenum complex (cf. 23 in Scheme 26) but intermediate organometallic species have not yet been isolated.53 Despite the relatively poor yields of 2H-pyrrole products, the process is synthetically valuable since the equivalent uncatalyzed photochemical process produces isomeric 2H-pyrroles from a primary reaction of azirine C—C cleavage54 (Scheme 24). 

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