Terminal alkynes oxidative cleavage

Alkynes, like alkenes, can be cleaved by reaction with powerful oxidizing agents such as ozone or KMnC, although the reaction is of little value and we mention it only for completeness. A triple bond is generally less reactive than a double bond and yields of cleavage products are sometimes low. The products obtained from cleavage of an internal alkyne are carboxylic acids from a terminal alkyne, CO2 is formed as one product. 

Terminal alkynes can be converted by a process of hydrosilylation followed by oxidative cleavage into carboxylic acids (10). An alternative basic" cleavage yields the corresponding aldehydes. 

Oxidative cleavage of alkenes, terminal alkynes, or aromatic rings... 

Oxidative cleavage of olefins, terminal alkynes, or aromatic rings 9-11 Oxidation of aromatic side chains 9-21 Oxidation of amines 9-22 Oxidation of primary alcohols or ethers... 

Terminal alkynes are prone to undergo facile oxidative cleavage to yield carboxylic acids with loss of the terminal carbon atom. In fact, most of the oxidizing agents that can be used in the selective oxidation of internal alkenes to 1,2-diketones [Ru04,711 PhIO with Ru catalysts,712 KMn04,713 T1(N03)3,716 0s04718] convert terminal alkynes to carboxylic acids. 

Terminal alkynes under these conditions undergo oxidative cleavage to the carboxylic acid, presumably because the intermediate keto aldehyde would yield the unstable a-keto acid. 

Aldehydes, RCHO (Sec. 7.9) (Sec. 7.9) (Sec. 8.4) (Sec. 17.7, 19.2) (Sec. 19.2, 21.6) from disubstituted alkenes by ozonolysis from 1,2-diols by cleavage with sodium periodate from terminal alkynes by hydroboration followed by oxidation from primary alcohols by oxidation from esters by reduction with DIB AH [HA1(i-Bu)2]... 

Alkynes also undergo oxidative cleavage of the a bond and both n bonds of the triple bond. Internal alkynes are oxidized to carboxylic acids (RCOOH), whereas terminal alkynes afford carboxylic acids and CO2 from the sp hybridized C - H bond. 

Terminal alkynes undergo the similar oxidative cleavage to afford carboxylic acids (Eq. 3.46), vhile internal alkynes are converted to diketones (Eq. 3.47) [79]. 

Under different reaction conditions, vicinal diol production [70] or C=C double bond oxidative cleavage to carboxylic acids occurs [59, 71], Dialdehydes are produced from cycloolefins, by tungstic acid as catalyst in t-butanol [72], Secondary alcohols yield ketones, while primary alcohols produce aldehydes or carboxylic acids [59, 68-69, 73-74], Different products are obtained from glycols, under different reaction conditions, 1,2-Diols are cleaved to ketocarboxylic acids and dicarboxylic acids [58, 75], or oxidised to a-hydroxy ketones [76], The latter can be obtained directly from the olefins, with lower selectivity [77], Lactones are formed by 1,4-diols and other a,o)-diols [78], Internal alkynes predominantly yield a,p-epoxyketones [79], or 1,2-diketones and carboxylic acids if HgfAcO) is added as the cocatalyst [80], Terminal alkynes yield a-ketoaldehydes and carboxylic acids. 

Secondly, it should be noted that virtually all of the reactions involve disub-stituted alkynes only one example of the cleavage of a terminal alkyne, that of Me3SiC=CH at a tricobalt center, had been reported by Vollhardt before our work detailed below. This is clearly because in most cases other more favorable processes, such as oxidative addition or vinylidene formation, intervene. 

Ochiai and coworkers have developed an efficient iodoarene-catalyzed oxidative cleavage of alkenes and alkynes using mCPBA as a terminal oxidant [40], Various cyclic and acyclic alkenes as well as aliphatic and aromatic alkynes are smoothly cleaved to carboxylic acids under these organocatalytic conditions (Scheme 4.15) [40]. 

C-Glycosidation of enol silane 279 to lactol acetate 278, prepared from 277 in two steps, furiushed ynone 280 as a single isomer. Reduction of the ketone with L-selectride furnished alcohol 270 with poor selectivity, but the minor isomer can be converted into the desired isomer via the Mitsunobu protocol Dihydroxylation of the terminal alkene, reduction of alkyne, and oxidative cleavage of the resulting triol gave the intermediate hydroxy aldehyde, which was spontaneously transformed into macrolactol 281 as a single diastereomer. 

When a terminal alkyne undergoes oxidative cleavage, the terminal side is converted into carbon dioxide ... 

Nucleophilic addition of 5-substituted tetrazoles (501) to ethynyl-phosphonate (500) proceeded regio- and stereoselectively to yield (Z) p-amino-p-tetrazolylvinylphosphonates (502) and (503) via attack of the N-1 (predominantly) or N-2 atom of the tetrazole at the C-2 atom of the triple bond of the phosphonate (500), respectively (Scheme 149)/ Treatment of p-ketophosphonates (504) with terminal alkynes (505) in the presence of an rhenium catalyst and under neutral conditions afforded 2i -l,2-oxaphosphorin 2-oxides (507). The reaction proceeded via cleavage of a C-C a-bond of the p-ketophosphonate (504), regio- and stereoselective insertion of the allq ne (505), followed by cyclisation of the resulting 5-phosphonyl a,p-unsaturated ketone (506) (Scheme 150). ... 

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