Intermediates, diacetylene

The dithienyl itself was shown to act as precursor of terthienyl (found in Echinops sphaerocephalus) by way of an intermediate diacetylenic dithienyl ... 

As in the reaction of diacetylene with alcohols (00UK642), the addition of glycols seems to start with attack at the terminal carbon atom of diacetylene, but no intermediate hydroxyl-containing enyne ether was isolated. 

Carbanions of substituted diacetylenes 68 generated under the action of complex superbase -BuLi/t-BuOK/THF/hexane add to carbon disulfide to afford the intermediates 69 which further transform to thieno[2,3-i]thiophenes (70) (90DIS 91SC145). 

Sixl, H. Spectroscopy of the Intermediate States of the Solid State Polymerization Reaction in Diacetylene Crystals. Vol. 63, pp. 49 — 90. 

Figure 8. Solid-state polymerization of diacetylenes. A crystalline array of monomer units polymerizes through intermediate states to the final crystalline polymer chain.

An interesting variation is the reaction of a diacetylene on cpCo(diene) systems [Eq.(24)J. 1,7-Octadiyne Initially undergoes an intramolecular process to give a nonisolable intermediate containing a cyclohexane ring. 

Enyne ethers HC=CCH=CHOR are useful synthetic intermediates. They can be prepared by base-catalysed addition of alcohols to diacetylene. The required conditions are rather forcing and not very attractive for laboratory scale preparations. A much more convenient way to prepare the enyne ethers (in these cases more than 80 rel.% of the -isomer is obtained) consists in treatment of the easily accessible 1,4-dialkoxy-2-alkynes with two equivalents of alkali amide in liquid ammonia. The first step in this elimination is the (transient) formation of an "anion RO-fiH-C CCH OR, which eliminates ROH (143). The resulting cumulenic ether ROCH=C=C=CH2 is immediately converted into the metallaied enyne ether. 

Reaction of thiophene or of 2-alkylthiophenes with butyllithium in the presence of HMPT is suggested to lead to the generation of dilithio intermediates (12), which are then cleaved in the usual way (entry 2 in Table I) the use of HMPT is critical in bringing about ring cleavage. 3,4-Dilithio species (13) give conjugated diacetylenes as products (see entries 17 and 26). 

Figure 5.4. The polymerisation of diacetylenes, (a), (b) and (c) are various possible intermediate structures. A dot denotes a free radical and two dots a free diradical. This figure is reproduced by kind permission of the authors and publishers from Polydiacetylenes, Synthesis, Structure and Electronic Properties by Bloor, D. and Chance, R.R. 1985 (Kluwer Academic, Dordrecht).

Oxidative addition of the copper(I) acetylide to the alkynyl halide with formation of a copper(III) intermediate (15), giving the corresponding diacetylene by reductive elimination [11a]. 

The aim of this article is to provide an overview of the polymerization of diacetylenes. The focus will be on optical excitation, although some results on thermal reactivity will also be quoted to illustrate analogies. Comprehensiveness is not intended, instead, emphasis will be placed on model considerations. Structural aspects of the polymerization process, as well as the low temperature spectroscopy of reaction intermediates will only briefly be addressed since they are treated in detail in the contributions of V, Enkelmann and H. Sixl in this volume. 

This contribution gives a review of recent spectroscopic investigations concerning the photophysical and photochemical primary and secondary processes of the solid state polymerization reaction in diacetylene single crystals. It will be shown, that diacetylenes are an unique model system for the study of the reaction mechanism of a solid state chemical reaction which is characterized by a variety of reaction intermediates. The polymerization reaction in these crystals is of special importance, due to the resulting polymer single crystals, which exhibit extraordinary anisotropic physical properties. 

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