Terminal diacetylene

Decreasing the temperature still further (80-90°C), the authors managed to obtain even the unstable terminal diacetylene, l,3,5-trimethyl-4-butadiynylpyrazole (yield 45%) (69KGS1055) (Scheme 95). 

Only two general methods have been developed for the synthesis of the macrocyclic annulenes.9 The first of these, developed by Sondheimer and co-workers, involves the oxidative coupling of a suitable terminal diacetylene to a macrocyclic polyacetylene of required ring size, using typically cupric acetate in pyridine. The cyclic compound is then transformed to a dehydroannulene, usually by prototropic rearrangement effected by potassium i-butoxide. Finally, partial catalytic hydrogenation of the triple bonds to double bonds leads to the annulene. 

The oxidative coupling of long-chain terminal diacetylenes carried out in very dilute solutions gives macrocyclic diacetylenes and polyacetylenes... 

Figure 2.3.12 Wireframe representations of the co-crystals involving the terminal diacetylene reactant (a) before reaction (b) after complete reaction.

Figure 2 shows the TEM images of microstructures made from amino acid terminated diacetylene lipids. For L-Glu-PDA (Fig. 2A), the aggregate consists of twisted and untwisted ribbons and fibers, with their lengths var5ring from... 

Until 2003 [11] no single crystal to single crystal transformation of a monosubstituted diacetylene to polydiacetylenes had been reported [27]. The Cambridge Structural Database contains only four entries for terminal diacetylenes and none of these have the supramolecular structural features necessary for a topochemical 1,4-polymerization as outlined in Scheme 5.1. There are many reasons for the lack of information on the topochemical polymerization of unsymmetrical monosubstituted diacetylenes. One is that the oxidative coupling procedure, readily applied for the preparation of symmetrical diacetylenes, is not easily applied to the preparation of unsymmetrical diacetylenes. Another factor is that unsymmetrical diacetylenes lack a center of symmetry and are less likely to pack with simple translational symmetry, a structural feature commonly observed for diacetylenes that undergo a topochemical polymerization (see Scheme 5.1). 

Figure 5.6. The pale background drawing shows the structure of the 16 H2O terminal diacetylene monomer structure. The bold foreground drawing shows the structure of the shrinkage of the unit cell c axis and a 9% resulting polydiacetylene. The main motion is increase in crystal density.

There have been attempts to polymerize terminal diacetylenes. For example K. Inoue, N. Koga, H. IwAMUA,/. Am. Chem. Soc. 1991, 113, 9803-9810. 

In the reactions of nucleophilic addition to diacetylene, monoalkylhydrazines behave in two ways (71AKZ743). In an anhydrous medium at 40-50°C, the reaction with methyl- and ethylhydrazines proceeds in such a way that a more nucleophilic disubstituted nitrogen atom attacks the terminal carbon atom of diacetylene to form l-alkyl-3-methylpyrazoles (17), the content of isomeric 1-alkyl-5-methylpyrazoles being 15% according to GLC (71AKZ743 73DIS 77AKZ332). 

In aqueous solutions, the prevailing process is the primary attack of the unsubstituted nitrogen atom of alkylhydrazines at the terminal carbon atom of diacetylene with predominant formation of l-alkyl-5-methylpyrazoles (18) (73DIS). The content of isomeric l-alkyl-3-methylpyrazoles is less than 10% (GLC). In the authors opinion, this different direction of the attack at diacetylene in aqueous media is related to the hydration of alkylhydrazines and the formation of ammonium base RN" H2(0H) NH2, in which the primary amino group becomes the major nucleophilic center. 

The reaction of disubstituted diacetylenes with hydrazine hydrate was reported by Darbinyan et al. (70AKZ640). In the first stage the addition of hydrazine to the terminal carbon atom of the diacetylene system is analogous to that of primary amines to diacetylene (69ZC108 69ZC110). With monosubstituted diacetylenes (R = H), hydrazine adds to the terminal triple bond. This leads to the formation of vinylacetylenic hydrazine 22 which cyclizes to dihydropyrazole 23 subjected to further isomerization to the pyrazole 25. It is possible that hydrazine 22 undergoes hydration to the ketone 24 which can easily be cyclized to the pyrazole 25... 

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. 

Diacetylene homologs are involved in this reaction by terminal acetylene bond to form monoadducts 5-alkynylpyrazoles 82 (65ZOR610). 

The addition of benzyl azide to monosubstituted diacetylenes initially proceeds at the terminal acetylene bond to form two regioisomeric 4- and 5-ethynyl-1,2,3-triazoles 98 and 99 along with minor amounts of the corresponding diadducts (81ZOR741 82ZOR1619). 

Terminal acetylenes such as phenylacetylene are transformed by Znl2, CuCl, CuBr, or CuCN and BTSP 1949 into 1-iodo- 1976, 1-chloro- 1978, 1-bromo- 1979, or l-cyano-4-phenylaIkynes 1980 and to the diacetylene 1977 [156] (Scheme 12.44). 

Diacetylenes having an internal and a terminal triple bond can be reduced selectively at the internal triple bond if they are first converted to sodium acetylides at the terminal bond by sodamide prepared in situ from sodium in... 

An alternative view of the polysilane structure is depicted using the worm-like model as proposed for poly(diacetylene)s59, where the linear chain has a large number of small twists without sharp twists playing a special role60-62. In this model, a Gaussian distribution of site energies and/or exchange interactions and the coherence of the excitation is terminated by any of the numerous usual random deviations from perfect symmetry. 

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