Synthesis of aryl and heterocyclic acetylenes via copper acetylides

Abstract

Ethynylbenzene (I), 1-ethynylnaphthalene (IX), 2-ethynylthiophen (IV), and 2-ethynyl-5-iodothiophen (XII) have been prepared from the corresponding iodo-derivatives (V), (VII), (II), and (X), by reaction with copper(I) 3,3-diethoxyprop-1-ynide to give αβ-acetylenic aldehydes, followed by base-catalysed deformylation. Alternatively, copper(I) 3-tetrahydropyranyloxy-prop-1-ynide gave the αβ-acetylenic alcohols (XVIII), (XIX), (XIII), (XX), and (XV), which were oxidised with nickel peroxide and then deformylated, or oxidised in aqueous alkali directly, to the same acetylenes (I), (IX), (IV), (XII), and 5-ethynyl-2,2′-bithienyl (XVII). The application of this sequence to the protection of terminal ethynyl groups is indicated.