Alkynes, with alcohols

Alkoxy-l,3-dioxoles are best prepared using the Diels-Alder methods discussed in Section 4.30.3.2.3. The corresponding 1,3-oxathioles are not well known, but have been reported from the reaction of l-(acylthio)-l-alkynes with alcohols (74RTC99), as shown in equation (49). 1,3-Dioxolanes and 1,3-oxathiolanes containing a 2-alkoxy substituent are easily prepared using an orthoester and a glycol or 2-mercaptoalcohol. 

Zhang W, Haight AR, Hsu MC (2002) Palladium-catalyzed coupling of alkynes with alcohols and carboxylic acids. Tetrahedron Lett 43 6575-6578... 

CO. Alkynes will react with carbon monoxide in the presence of a metal carbonyl (e.g. Ni(CO)4) and water to give prop>enoic acids (R-CH = CH-C02H), with alcohols (R OH) to give propenoic esters, RCH CHC02R and with amines (R NH2) to give propenoic amides RCHrCHCONHR. Using alternative catalysts, e.g. Fe(CO)5, alkynes and carbon monoxide will produce cyclopentadienones or hydroquinols. A commercially important variation of this reaction is hydroformyiation (the 0x0 reaction ). 

The direct combination of selenium and acetylene provides the most convenient source of selenophene (76JHC1319). Lesser amounts of many other compounds are formed concurrently and include 2- and 3-alkylselenophenes, benzo[6]selenophene and isomeric selenoloselenophenes (76CS(10)159). The commercial availability of thiophene makes comparable reactions of little interest for the obtention of the parent heterocycle in the laboratory. However, the reaction of substituted acetylenes with morpholinyl disulfide is of some synthetic value. The process, which appears to entail the initial formation of thionitroxyl radicals, converts phenylacetylene into a 3 1 mixture of 2,4- and 2,5-diphenylthiophene, methyl propiolate into dimethyl thiophene-2,5-dicarboxylate, and ethyl phenylpropiolate into diethyl 3,4-diphenylthiophene-2,5-dicarboxylate (Scheme 83a) (77TL3413). Dimethyl thiophene-2,4-dicarboxylate is obtained from methyl propiolate by treatment with dimethyl sulfoxide and thionyl chloride (Scheme 83b) (66CB1558). The rhodium carbonyl catalyzed carbonylation of alkynes in alcohols provides 5-alkoxy-2(5//)-furanones (Scheme 83c) (81CL993). The inclusion of ethylene provides 5-ethyl-2(5//)-furanones instead (82NKK242). The nickel acetate catalyzed addition of r-butyl isocyanide to alkynes provides access to 2-aminopyrroles (Scheme 83d) (70S593). 

Scheme 5.1-27 The zinc triflate-catalyzed coupling of alkynes with aldehydes to give propargyl alcohols in an ionic liquid.

Both aliphatic and aromatic terminal alkynes reacted with aliphatic aldehydes giving exclusively a mixture of ( ,Z)-1,5-dihalo-1,4-dienes and disubstituted ( )-a,p-unsaturated ketones, the former being the major products in all cases. When nonterminal aromatic acetylenes were used, the trisubstituted ( )-a,p-unsat-urated ketones were the exclusive compounds obtained. The procedure was not valid for ahphatic and unsaturated alkymes. However, the catalytic system was found to be compatible with alcohols and their corresponding acetates although limited yields were obtained. 

FeCl3 6H20 turned out to be the catalyst of choice for this reaction, since the presence of water improved the yield. However, high yields of the desired ketones were obtained for electron-rich alkynes with anhydrous FeCla at room temperature. Alcohols that are sensitive to acid-catalyzed dehydration were also tolerated under the present conditions (R = Me or Et). Based upon experimental observations a mechanism for this reaction was proposed (Scheme 14). 

Related to these strategies, Fe(OTf)3/TfOH cocatalyzed the coupling reaction of terminal alkynes with benzylic alcohols in the absence of base by means of a sp-sp C-C bond formation (Scheme 16) [32]. 

The mechanism of the methoxycarbonylation of alkynes667-669 promoted by the Pd(OAc)2/ PPh2(pyc)/CH3S03H catalytic system has been reported. Experiments carried out using 1-alkynes and CH3OD and 111 NMR reveal that the catalyst also promotes the exchange of the terminal hydrogen of the alkyne with the deuterium of the alcohol.677... 

Many other reactions designed to trap intermediate vinylketene complexes are known. Dotz has used alkynes with a pendant alcohol to produce the butyrolactones E-31 and Z-31 in a 70 30 ratio and 34% yield.16 These are formed by the nucleophilic attack of the pendant alcohol on the ketene... 

Introduction of an alkyl group onto an aromatic substrate by treating the substrate with an alkylating agent such as alkyl halide, alkene, alkyne and alcohol in the presence of a Lewis acid. 

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