Oxidative cleavage alkynes

Thomsoni. Ov Click Organic Interactiveto use a web-based palette to predict products for the oxidative cleavage of alkynes. 

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 alkenes using sodium periodate proceeds effectively in a monophasic solution of acetic acid, water, and THF with very low osmium content or osmium-free. The orders of reactivity of alkenes are as follows monosubstituted trisubstituted >1,2 disub-stituted > 1,1-disubstituted > tetrasubstituted alkynes.100 Cleavage with polymer-supported OSO4 catalyst combined with NaI04 allows the reuse of the catalyst.101... 

There is a rich chemistry of alkene and alkyne oxidation by RuO. The main application lies in alkene cleavage, bnt there is growing interest in cw-dihydroxylation by the reagent. In the sections below we first consider oxidations which do not sever the C=C bond (epoxidation, ctT-dihydroxylation, ketohydroxylation), and then alkene cleavage reactions. 

This is one of the most important applications for RuO. Oxidative cleavage of alkenes and alkynes by a variety of reagents has been reviewed [30, 35, 50, 60, 68-71]. The gentler cleavage reactions of alkenes to aldehydes or ketones are considered first (Table 3.3), then the commoner cases of cleavage to carboxylic acids (Table 3.6). 

Oxidative cleavage of alkynes by a variety of reagents has been reviewed [35, 60, 70, 71]. In most cases the CC bond is broken, but in some cases a-diketones are formed instead of, or in addition to, carboxylic acids. Examples of both types of reaction are given in Tables 3.3 and 3.6. 

Table 3.6 Oxidative cleavage of alkenes to acids and alkynes to ketones or acids...

As with alkene cleavage the main reagent for alkyne oxidations is RuO. Oxidative cleavage of alkynes by a variety of reagents has been reviewed [4, 6, 12, 14, 15], The first oxidation of alkynes was noted by Pappo and Becker in 1956 they showed that l,2-fc/x(l-acetoxycyclohexyl)ethyne (2) (Fig. 1.5) gave the diketone. Minimal experimental details were given [195],... 

Problem 16.7 Account for the fact that on oxidative cleavage all substituted alkynes give carboxylic acids, whereas some alkenes give ketones. ... 

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. 

Oxidative cleavage of alkynes.1 This reagent (3 equiv.) cleaves 1-alkynes to the norcarboxylic acids in 55-80% yield. 

Oxidative cleavage of [CpMo(CO)3]2 is not the only route to cationic bisalkyne products. The electrophilic [CpMo(CO)3][BF4] reagent prepared by hydride abstraction from CpMo(CO)3H with [Ph3C][BF4] (99) readily adds alkyne to form monoalkyne and bisalkyne products depending on the reaction conditions and the alkyne substituents [Eq. (38)]. Bisalkyne products were best prepared from [CpMo(CO)2[P(OPh)3] [BF4] reagents (76). 

Alkyne ligands have been removed from metal complexes intact, in oxidized form, and in reduced form. In spite of accomplishing alkyne-metal cleavage with different reagents in specific cases, there is no general method for systematically separating an alkyne ligand from a d4 metal center. 

Oxidative cleavages can help to determine the positions of the triple bonds in alkynes. 

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