Alkynes terminal oxidation

Internal alkynes are oxidized to acytoins by thalliuin(III) in acidic solution (A. McKil-lop, 1973 G.W. Rotermund, 1975) or to 1,2-diketones by permanganate or by in situ generated ruthenium tetroxide (D.G. Lee, 1969, 1973 H. Gopal, 1971). Terminal alkynes undergo oxidative degradation to carboxylic acids with loss of the terminal carbon atom with these oxidants. 

Using a catalyst system of PdCl2, CuCH, HCl, and O2, the internal alkyne 20 is carbonylated at room temperature and 1 atm to give unsaturated esters[19]. This apparently oxidizing system leads to non-oxidative cu-hydroesterilica-tion. With terminal alkynes, however, oxidative carbonylation is observed. 

This reaction typifies the two possibilities of reaction routes for M-catalyzed addition of an S-X (or Se-X) bond to alkyne (a) oxidative addition of the S-X bond to M(0) to form 94, (b) insertion of alkyne into either the M-S or M-X bond to provide 95 or 96 (c) C-X or C-S bond-forming reductive elimination to give 97 (Scheme 7-21). Comparable reaction sequences are also discussed when the Chalk-Harrod mechanism is compared with the modified Chalk-Harrod mechanism in hydrosily-lations [1,3]. The palladium-catalyzed thioboratiori, that is, addition of an S-B bond to an alkyne was reported by Miyaura and Suzuki et al. to furnish the cis-adducts 98 with the sulfur bound to the internal carbon and the boron center to the terminal carbon (Eq. 7.61) [62]. 

SCHEME 127. Se02-catalyzed aUyUc oxidation of alkynes using TBHP as terminal oxidant... 

Eastmond, R. Johnson, T. R. Walton, D. R. M. Silylation as a Protective Method for Terminal Alkynes in Oxidative Couplings, Tetrahedron 1972,28, 4601. 

The MTO/H202 system has been used to oxidize several other classes of substrates. Internal alkynes may be oxidized to a-diketones and/or carboxylic acids, whereas terminal alkynes are oxidized to mixtures of carboxylic acids, -ketoacids, and (in alcoholic solvents) esters.49 These conversions are proposed to proceed through an oxirene intermediate by analogy to the alkene epoxidations discussed earlier. 

A copper catalysed click (azide-alkyne cycloaddition) reaction has been used to prepare a fluorous-tagged TEMPO catalyst (Figure 7.20). TEMPO is a stable organic free radical that can be used in a range of processes. In this case, its use in metal-free catalytic oxidation of primary alcohols to aldehydes using bleach as the terminal oxidant was demonstrated. The modified TEMPO can be sequestered at the end of the reaction on silica gel 60 and then released using ethyl acetate for reuse in further reactions in this way the TEMPO was used four times with no loss in activity. 

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. 

Both internal and terminal alkynes are oxidatively cleaved with ozone to give carboxylic acids. 

Internal alkynes yield carboxylic acids and a-diketones when oxidized with the MTO/H2O2 system [22]. Rearrangement products are observed only for aliphatic alkynes. Terminal alkynes give carboxylic acids, derivatives thereof and a-keto acids as the major products. The yields of these products vary with the solvent used [22]. 

Eastmond R, Johnson TR, Walton DRM. Silylation as a protective method for terminal alkynes in oxidative couplings. A general synthesis of the parent polyynes ll(C=C),H (w = 4-10,12). Tetrahedron 1972, 28, 4601. 

Another common class of lipopeptide from cyanobacteria includes a starter PKS lipid section, almost always found as an eight-carbon chain (exceptions being jamaicamide, carmabin, and palau amide ), in which oxidation of the Ci -terminus occurs to typically produce a terminal alkyne functionality. Such terminally oxidized PKS motifs can be further dissected into those with an overall linear structure, such as the jamaica-mides, ° apramides, dragonamides, carmabins, " and dragamabin, and those possessing a 3-hydroxy or... 

The same reagents that oxidize alkenes also oxidize alkynes. Alkynes are oxidized to diketones by a basic solution of KMn04 at room temperature and are cleaved by ozonolysis to carboxylic acids. Ozonolysis requires neither oxidative nor reductive work-up—it is followed only by hydrolysis. Carbon dioxide is obtained from the CH group of a terminal alkyne. 

The phase-transfer-assisted permanganate oxidation of alkynes and alkenes has been reviewed. Terminal and internal alkynes are oxidized to 1,2-dicarbonyl compounds by the combined action of diphenyl disulphide, ammonium peroxidisulphate and water or by sodium periodate in the presence of ruthenium dioxide (equation 34). Other reagents for the conversion of acetylenes into 1,2-dicarbonyl compounds are hydrogen peroxide in the presence of (2,6-dicarboxylatopyridine)iron(II), the complex oxo(A, A -ethylenebissalicylideneiminato)chromium(V) trifluoromethanesulphonate (216)and ruthenium tetroxide as a mediator in electrooxidation. l-Acetoxyalkan-2-ones 217 are obtained by the oxidation of terminal acetylenes with sodium perborate and mercury(II) acetate in acetic acid ". Terminal alkynes give a-ketoaldehydes 218 on treatment with dilute hydrogen peroxide, combined with mercury(II) acetate and sodium molybdate or sodium tungstate under phase-transfer conditions. ... 

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]. 

Terminal alkynes undergo oxidative coupling in the presence of the GuGl-TMEDA catalytic system in [G4GiIm]PF6 under aerobic conditions to produce 1,3-diynes. " Intermolecular Pauson-Khand reactions of strained alkenes with alkynes and Go2(GO)g were performed in [G4GiIm]PF6 either thermally or in the presence of... 

Muniz and co-workers prepared a series of substituted indoles (e.g., 76) using a modified Koser reagent that was made from iodosobenzene and 2,4,5-tris-isopropylbenzene sulfonic acid (77, TIPBSA). The hypervalent iodine reagent was used either stoichiometrically or in catalytic amounts with mCPBA as the terminal oxidant. A variety of N-protecting groups were tolerated and substituents on the aryl ring of 75 include halogens, carbonyls (aldehydes, ketones, esters), alkynes, and nitriles (HAG(I)7349). 

The earliest example of block copolymers made using CuAAC was from Opsteen and van Hest in 2005, when they coupled alkyne-terminated polymer with azide-terminated polymer in excellent yields to make several diblocks (see Scheme 4). While this example was an excellent proof of concept, the polymers formed (PS-PMMA, PS-poly(ethylene oxide (PEO), PMMA-PEO) can easily be synthesized by sequential CFR polymerizations, or by the use of PEO-based macroinitiators. It has, though, served as a template for researchers to use CuAAC to make block copolymers that might be prohibitively difficult or impossible to synthesize with only previously existing polymerization techniques. For... 

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. 

Isoxazoles display a range of biological activities, such as anti-inflammatory, antimicrobial, anticancer, and antinociceptive, that justify a constant effort in the development of new synthetic strategies. New syntheses of isoxazoles 1 and isQxazolines 2 via 1,3-dipolar cycloaddition (1,3-DC) of alkynes and alkenes with nitrile oxides were described (130L4010). The 1,3-dipoles were generated by oxidation of aldoximes catalyzed with hypervalent iodine species formed in situ from catalytic iodoarene and oxone as a terminal oxidant, in the presence of hexafluoroisopropanol (HFIP) in aqueous methanol solution. 

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