Hydrogen peroxide alkynes

Radical-mediated silyldesulfonylation of various vinyl and (a-fluoro)vinyl sulfones 21 with (TMSlsSiH (Reaction 25) provide access to vinyl and (a-fluoro)vinyl silanes 22. These reactions presumably occur via a radical addition of (TMSlsSi radical followed by /)-scission with the ejection of PhS02 radical. Hydrogen abstraction from (TMSlsSiH by PhS02 radical completes the cycle of these chain reactions. Such silyldesulfonylation provides a flexible alternative to the hydrosilylation of alkynes with (TMSlsSiH (see below). On oxidative treatment with hydrogen peroxide in basic aqueous solution, compound 22 undergoes Pd-catalyzed cross-couplings with aryl halides. 

Heteropoly acids can be synergistically combined with phase-transfer catalysis in the so-called Ishii-Venturello chemistry for oxidation reactions such as oxidation of alcohols, allyl alcohols, alkenes, alkynes, P-unsaturated acids, vic-diols, phenol, and amines with hydrogen peroxide (Mizuno et al., 1994). Recent examples include the epoxidations of alkyl undecylenates (Yadav and Satoskar, 1997) and. styrene (Yadav and Pujari, 2000). 

Alkynes are reactive toward hydroboration reagents. The most useful procedures involve addition of a disubstituted borane to the alkyne, which avoids complications that occur with borane and lead to polymeric structures. Catechol borane is a particularly useful reagent for hydroboration of alkynes.212 Protonolysis of the adduct with acetic acid results in reduction of the alkyne to the corresponding cw-alkene. Oxidative workup with hydrogen peroxide gives ketones via enol intermediates. 

Hydroboration-oxidation of alkynes preparation of aldehydes and ketones Hydroboration-oxidation of terminal alkynes gives syn addition of water across the triple bond. The reaction is regioselective and follows anti-Markovnikov addition. Terminal alkynes are converted to aldehydes, and all other alkynes are converted to ketones. A sterically hindered dialkylborane must be used to prevent the addition of two borane molecules. A vinyl borane is produced with anU-Markovnikov orientation, which is oxidized by basic hydrogen peroxide to an enol. This enol tautomerizes readily to the more stable keto form. 

Enantioselective, multiple centers 153, 166,189 Hydroamination Intermolecular Alkene 30 Alkyne 1 Intramolecular Alkene 30 Alkyne 13,170 Hydrogen peroxide Oxidation of alcohols 26, 86 Hydrogenolysis of epoxide 1 Hydrozirconation 32... 

Surprisingly, there is no literature precedent for the addition of either hydrogen peroxide or alkyl hydroperoxides to dienes, polyenes or alkynes. 

Terminal alkynes react rapidly with borane to produce an intermediate compound that is easily oxidized to an aldehyde. For example, you can produce pentenal by reacting pentyne with borane and oxidizing the resulting intermediate with aqueous hydrogen peroxide. 

An iridium(m) hydride catalyzed intramolecular alkyne hydroalkoxylation can be used to construct isochromans 545 bearing a C(3)-spiroacetal moiety (Equation 226) <2005OL5437>. Novel isochromans bearing an array of C(3)-spiroacetal moieties are accessible via the hydroboration of alkynediols with disiamylborane followed by treatment of the resulting alkenylboron compounds with alkaline hydrogen peroxide <1998CL81>. 

Oxidation of alkenylboranes by alkaline hydrogen peroxide gives aldehydes or ketones depending on the substituent pattern of the alkenyl group thus, when alkaline hydrogen peroxide oxidation is combined with alkyne hydroboration, the resulting two-step process is a procedure for converting alkynes to carbonyl compounds (Equations B2.7 and B2.8). 

The hydroboration reaction is also useful with alkynes. As is shown in the following example, the product after treatment with basic hydrogen peroxide is an enol. As we have seen before, the enol cannot be isolated because it spontaneously tautomerizes to a ketone. This provides another way to hydrate alkynes to produce ketones. 

Hexyne has the triple bond in the middle of a carbon chain and is termed an internal alkyne. If, instead, an alkyne with the triple bond at the end of the carbon chain, a 1-alkyne or a terminal alkyne, were used in this reaction, then the reaction might be useful for the synthesis of aldehydes. The boron is expected to add to the terminal carbon of a 1-alkyne. Reaction with basic hydrogen peroxide would produce the enol resulting from anti-Markovnikov addition of water to the alkyne. Tautomerization of this enol would produce an aldehyde. Unfortunately, the vinylborane produced from a 1-alkyne reacts with a second equivalent of boron as shown in the following reaction. The product, with two borons bonded to the end carbon, does not produce an aldehyde when treated with basic hydrogen peroxide. 

Oxidation of the vinylborane (using basic hydrogen peroxide) gives a vinyl alcohol (end), resulting from anti-Markovnikov addition of water across the triple bond. This end quickly tautomerizes to its more stable carbonyl (keto) form. In the case of a terminal alkyne, the keto product is an aldehyde. This sequence is an excellent method for converting terminal alkynes to aldehydes. 

Figure 3.109 In situ bromination of alkenes and alkynes using hydrogen bromide in the presence of hydrogen peroxide.

Although oxidation of l,l-bis(dialkylboryl) compounds with alkaline hydrogen peroxide proceeds with initid hydrolysis rather than oxidation (equation 16), oxidation with excess MCPBA yields carboxylic acids in good yields. The overall process is an excellent route from 1-alkynes to carboxylic acids (equation 39). ... 

Synthesis of secootkiry eokois from l-aOtynes. Dihydroboration at room temperature of a terminal alkyne with either (I) or 9-BBN gives a 1,1-diborylalkane (3) this is treated at 0-5° with I eq. of methyllithium in ether. The product (4) rearranges to (S). An alkyl halide (100 excess) is then added, and the resultant secondary organo-borane (6) is oxidized with alkaline hydrogen peroxide. Secondary alcohols (7) are obtained in 70-85% yield. 

Acylsilanes may serve as synthetic equivalents of cai boxylic acids when treated with alkaline hydrogen peroxide. Especially attractive is the one-pot conversion of the ethynyl group of 1-alkynes into monosubstituted acetic acids via sequential silylation, hydroboration, and oxidation, as depicted below. 

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