Additions to Acetylenes

Addition of HOCl to vinyl chloride yields chloroacetaldehyde (106) addition to acetylenic compounds produces dichloroketones (107) (see... 

Examples of photochemical methods of addition to acetylene derivatives are the addition of methyl disulfide to hexafluoro-2-butyne [7] (equation 8), of trifluaramethanethial to methyl propiolate [S] (equation 9), of methanethiol to trifluoromethylacetylene and hexafluoro-2-butyne [9] (equation 8), and of tri-methylsilane to tetrafluoropropyne [10. ... 

The addition of secondary amines to acetylenes is most applicable to the synthesis of conjugated acyclic enamines (50,171,172). Particularly the addition to acetylenic esters and sulfones has been investigated (173-177) and it appears that an initial trans addition is followed by isomerization to more stable products where the amine and functional group are in a trans orientation (178). Enamines have also been obtained by addition of secondary amines to allenes (179). 

Nucleophilic addition to acetylenic sulfoxides provides a,/ -ethylenic sulfoxides. Treatment of 181 with monoalkyl-copper afforded nearly quantitatively /J-alkylated a, / -ethylenic sulfoxides 182 through cis-addition to the triple bond. The reaction with lithium dimethylcuprate also afforded a similar adduct however, the reaction with lithium di-n-butylcuprate was found to give a small amount of ethyl n-butyl sulfoxide 183 besides the... 

Summary of Electrophilic Additions to Acetylenes and Allenes Involving Vinyl Cations... 

It is also difficult to determine exactly the relative stabilities of vinyl cations and the analogous saturated carbonium ions. The relative rates of solvolysis of vinyl substrates and their analogous saturated derivatives have been estimated to be 10 to 10 (131, 134, 140, 154) in favor of the saturated substrates. These rate differences, however, do not accurately reflect the inherent differences in stability between vinyl cations and the analogous carbonium ions, for they include effects that result from the differences in ground states between reactants, as well as possible differences between the intermediate ions resulting from differences in solvation, counter-ion effects, etc. The same difficulties apply in the attempt to estimate relative ion stabilities from relative rates of electrophilic additions to acetylenes and olefins, (218), or from relative rates of homopropargylic and homoallylic solvolysis. 

This disilene undergoes Diels. Alder reaction with 1, 3 diene addition to acetylene and a single example of reaction with a carbonyl system. 

When acetylenes, or alkenes having an electron-withdrawing group attached to the carbon-carbon double bond, are added to the solution t-BuSOH undergoes rapid addition to the triple or double bond in the fashion shown in (4) and (5). The addition to acetylenes was shown to take place stereo-specifically in a cis fashion. 

Silicones can be prepared in such a way that they contain only one percent or less of vinyl groups and silicon hydrides, which undergo a catalytic hydrosilylation reaction to give the desired cross-linking (Figure 18.3). Vinyl silanes are made by Si-H addition to acetylene, and thus two hydrosilylations are involved. 

Many valuable reviews of the chemistry of these species are given in the new book Dicoordinated Carbocations An introduction by Grob " is followed by reviews of various theoretical studies of vinyl cations, their gas-phase chemistry, their generation by nuclear decay, and their NMR spectroscopic characterization. Vinyl cation production by addition to acetylenes and allenes, by solvolysis, and photolytically are covered, together with the chemistry of the species generated in these various ways. The next chapter deals with the synthetic applications of vinyl cations,and alkynyl and aryl cations are covered in the last chapter. A review of the NMR spectroscopic and quantum-chemical investigation of vinyl cations in superacid media (also of dienyl and 1-cyclopropylvinyl cations) is published separately,as is a review of alkynylcar-... 

Organyl tellurolate anions effect 1,4-additions to acetylenes bearing electron-withdrawing groups such as acetylenic ketones, aldehydes, esters, diacetylenic ketones, " as well as acetylenic phosphonates and sulphones giving 2-substituted vinyl tellurides with Z configuration. 

Until recently it was often difficult to assign structures to the isomeric triazoles formed in additions to acetylenes. There are now several useful NMR criteria (Section III,B) which can help to distinguish the isomers. 

Relatively few additions of the lower molecular weight alkyl azides have been performed, mainly because of their volatility and thermal sensitivity simple alkyltriazoles are normally obtained by alkylation of the w-triazoles. On the other hand, a very wide range of less volatile substituted alkyl azides has been added to acetylenes Their addition to acetylenic esters usually proceeds readily and provides a useful method of characterizing the azides. Benzyl azide has often been used because it is relatively stable (up to 150°), it is readily prepared, and the benzyl group can be removed from the resulting triazoles (Section IV, E). 

Cyanogen azide is less stable than most azides, and few additions have been attempted. Addition to acetylene and to alkynesgives the triazoles, which, like some sulfonyltriazoles, exist in equilibrium with open-chain tautomers. 

In general, acyl azides are too unstable to survive at the temperatures required for addition to acetylenes, although benzoyl azide adds readily to ynamines in toluene. Ethoxycarbonyl azide also gives triazoles in good yield with ynamines. The azide adds to propargylic alcohols in boiling ethanol, and to acetylene at 100° under pressure. Addition to phenylacetylene and to electron-deficient acetylenes has been carried out at 130°. Oxazoles are also formed at this temperature by competing thermal decomposition of the azide, and addition of ethoxycarbonylnitrene to the acetylenes. The triazole obtained from phenylacetylene is 2-ethoxycarbonyl-4-phenyltriazole the two 1-ethoxycarbonyltriazoles can be isolated if the addition is carried out at 50° over several weeks. Since the IH- to -triazole isomerization takes place readily in these systems, a IH-structure cannot be assumed for a triazole formed by addition of these azides. 

Additions to acetylenes have been carried out with many other types of azide, including glycosyl azides, various heterocyclic azides ... 

Synthesis of Heterocycles through Nucleophilic Additions to Acetylenic Esters... 

Secondary amines, such as dimethylamine, diethylamine, diisopropylamine, dicyclohexylamine, A(-methylaniline, aziridine, and azetidine, are reported to undergo cis addition to acetylenic esters, giving rise to simple 1 1 Michael adducts, in each case. These adducts have been successfully employed in the synthesis of different heterocyclic compounds. 

Thiophenols undergo base-catalyzed, Michael addition to acetylenic acids and esters to give trans addition products. These vinyl thioethers have been used in the synthesis of thiochromones. " Recently, Undheim and Lie have shown that thiophenol adds to DMAD with concomitant cyclization to give benzo[6]thiophenes. 

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