Other Reactions of Acetylenes

Other Reactions of Acetylenes.—Several recent papers have been concerned with the mechanism of nucleophilic displacement at acetylenic carbon. In the halide displacement from halogenoacetylenes, substitution is feasible by either a-addition and / -elimination [reaction (4)] or by attack on the halogen atom with subsequent attack by the acetylide anion [reaction (5)]. 

Viehe and Delavarenne have suggested a third possibility which includes j5-addition, a-elimination, and onium rearrangement [reaction (6)] similar to the mechanism of the Frisch-Buttenberg-Wiechell rearrangement. Their 

Phenylethynyl ethers may be obtained from phenylchloroacetylene by treatment with alkoxide ion in aprotic solvents. A detailed study of the reaction of phenylchloroacetylene has shown the latter to be triphilic towards methoxide ion with 99 % of the attack occurring at the carbon bearing the chlorine. With phenylbromoacetylene the corresponding figure is 83 %.  

Acetylenes generally react with carbenes to form cyclopropenes. Whether this is a reaction via a singlet carbene or a two-step process via a biradical cannot be determined from the product, as is the case in the trapping with olefins. Isolation of indenes (116) from the reaction of acetylenes with di-phenylcarbene generated photochemically from the diazo-compound, however, was considered to be evidence for the intermediacy of a triplet carbene. 

Among Cope rearrangements involving acetylenes is the thermolysis of hex-5-en-l-yn-3-ol. The products were all considered to be derived by further 

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The monograph presents a modern methodology of regioselective synthesis of aromatic and nonaromatic carbocyclic and heterocyclic ring systems based mainly on [2+2+2] and [4+2] cycloaddition, and other reactions of acetylenic units, including enediynes and enyne-allenes. The features of the construction of polyaromatic structures, including heterostructures, based on cycloaddition reactions is used in the synthesis of advanced materials including nanomaterials. 

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