Terminal acetylene oxidation

Thalllum(III) Compounds. Tb allium (ITT) derivatives have been used extensively as oxidants in organic synthesis. In particular, thaUic acetate and ttifluoroacetate are extremely effective as electrophiles in oxythaHation and thaHation reactions. For example, ketones can be prepared from terminal acetylenes by means of (OOCCH ) in acetic acid (oxythaHation) (30) ... 

Methyl ketones are important intermediates for the synthesis of methyl alkyl carbinols, annulation reagents, and cyclic compounds. A common synthetic method for the preparation of methyl ketones is the alkylation of acetone derivatives, but the method suffers limitations such as low yields and lack of regioselectivity. Preparation of methyl ketones from olefins and acetylenes using mercury compounds is a better method. For example, hydration of terminal acetylenes using HgSO gives methyl ketones cleanly. Oxymercuration of 1-olefins and subsequent oxidation with chromic oxide is... 

A similar phenomenon was observed for 3-amino- and5-amino-4-iodopyrazoles. The anomalous reaction in which the products of oxidative coupling of terminal acetylenes (up to 90%) are present along with the products of deiodination (up to 90%) has been described for the first time [99JCS(P1 )3713] and will be considered below in the part related to cross-coupling of 4-iodopyrazoles. 

The efficient formation of diaryliodo-nium salts during the electrolysis of arylio-dides has been reported by Peacock and Fletcher [166]. The electroiodination of a 3D-aromatic molecule, dodecahydro-7,8-dicarba-nido-undecaborate has also been reported [167]. The iodination (and bromi-nation) of dimedone has been reported to yield 2-iododimedone, which formally is an electrophilic substitution reaction [123]. In a similar process, the indirect electrochemical oxidation of aliphatic ketones in an alkaline Nal/NaOH solution environment has been shown to yield a,a-diiodoketones, which rapidly rearrange to give unsaturated conjugated esters [168]. Dibenzoylmethane has been converted into dibenzoyliodomethane [169]. Terminal acetylenes have been iodinated in the presence of Nal. However, this process was proposed to proceed via oxidation of the acetylene [170]. 

Oxidative carbonyiation. Terminal acetylenes are converted into acetylene-carboxylales by CO (1 atm.) and an alcohol in the presence of a catalytic amount of PdCl2 and 1 equivalent of CuCl2. In addition a base such as sodium acetate is necessary. The reaction is an oxidative carbonyiation with PdCl2, which is reduced to Pd(0). PdCl2 can be used in catalytic amounts if CuCl2 is available for oxidation of Pd(0) to PdCl2. The base is needed to neutralize the HCI formed (equation I). The yields of the carboxylate are 60-75%. ... 

In contrast to the preceding reagents, oxidation with H202 catalyzed by molybdate and tungstate salts or Hg(OAc)2,722,723 and the Hg(OAc)2-promoted oxidation with a molybdenum peroxo complex724 can be applied to transform acetylene and terminal acetylenes to glyoxal and a-ketoaldehydes, respectively, in fair to good yields. 

Oxidative coupling of terminal acetylenes in the presence of copper(I) catalysts is the best method of preparing symmetrically substituted butadiyne derivatives,5 and has been applied to the coupling of trimethylsilyl-acetylene. Better yields are obtained using the Hay procedure in which the catalyst is the TMEDA complex of copper(I) chloride.7 The procedure submitted here is an improved version of Walton and Waugh s synthesis of BTMSBD by the Hay coupling of trimethylsilylacetylene.2 BTMSBD has also been prepared by... 

Compounds with a terminal acetylenic function, RCsCH, react with 1-bromoalkynes, R CsCBr in the presence of an aliphatic amine and a catalytic amount of a copper salt to give the coupling products RCsCCsCR. This useful reaction, discovered by Cadiot and Chodkiewicz [195], gives a ready access to a number of poly-unsaturated systems. The usual procedure involves dropwise addition of the bromoacetylene R GsCBr to a mixture of the acetylene RCsCH, ethylamine, ethanol or methanol, a catalytic amount of copper chloride or bromide and a small amount of hydroxylamine.HCl. This reducing agent prevents the oxidation to copper ). The reaction is usually very fast at temperatures in the region of 30 C. Since much heat is evolved, the reaction can be monitored easily by temperature observation. 

Silver(I)-catalyzed cyclizations of substituted allenes to heterocydic ring systems induding 2,5-dihydropyrroles have been described previously [4,10]. Moreover, sil-ver(I) salts are known to form stable rr-complexes with terminal acetylenes [11]. On the other hand, on treatment with silver nitrate silylacetylenes were reported to afford silver acetylides [12]. Based on these considerations and additional experimental evidence [5,13], the following mechanism has been proposed forthe sUver(I)-mediated oxidative cydization of homopropargylamines to pyrroles ]5] (Scheme 15.3). 

The THT and SMe2 adducts have structures of the type (18-B-V). Their chemistry has been extensively studied and it is summarized in Fig. 18-B-7. The diverse, and in some cases unique, reactivity of these compounds includes substitution with preservation of the geometry or with conversion to (MX4)2(/t-X)2 species, oxidative-addition,53 cluster formation, splitting of C—N bonds,54 and above all coupling of the molecules with triply bonded carbon atom.55 They catalytically trimerize and polymerize terminal acetylenes, and dimerize nitriles and isonitriles with incorporation of the new ligand into the complex. Another remarkable reaction of M2C16L3 is the metathesis of M=M and N=N bonds into two M=N bonds upon reaction with azobenzene. 

Bauerle and co-workers have synthesized a macrocycle consisting of 8 thiophenes in conjugation by an oxidatively induced elimination of platinum complexes <03CC948>. The platinum complexes 55 were obtained by reaction of terthiophene with terminal acetylenic groups with cw-Pt(dppp)Cl2 in the presence of Cul and EtsN. C-C bond formation was effected by oxidatively induced elimination using iodine and the diacetylene bridged thiophene macrocycle 56 was converted to an all thiophene macrocycle 57 by reacting with sodium sulfide. 

Intermolecular oxidative addition of H—C usually involves activated H—C bonds. The weak acid HCN reacts with transition-metal complexes e.g., HCN and NiL lead to the hydride complexes HNi(CN)Lj (L = various phosphorus ligands). The versatile complex IrCl(CO)(PPh3)j adds HCN cleanly in CH Clj at RT to form HIr(CN)(Cl(PPhj)2. The zero-valent complexes Pt(PPhj) or Pt(PPh3)3 also add HCN to yield HPt(CN)(PPh3)j. Reactions of HMNp(dmpe)j (M = Fe, Ru, Os Np = 2-naphthyl dmpe = Me PCH CH PMej) with HCN and terminal acetylenes give HMR(dmpe)2 that contain new M—C bonds (R = — CN, — CjR ) . 

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