1,3-Hexadiyne

The product is rather volatile, with an estimated b.p. between 100 and 110 C at 760 mmHg. If the ethylation was carried out at the b.p. of ammonia and this solvent allowed to evaporate, 5-10% of the product would be lost. For this reason and also in view of the limited thermal stability of 1,3-hexadiyne (danger of explosive decomposition at elevated temperatures) we propose a work-up procedure similar to that used in exp. 3. 

A pyrrole synthesis leading to 20 has been achieved by a CuBr catalyzed cyclization of the intermediate imine 21, which was prepared over several steps from 1,3-hexadiyne (22) in a one-pot operation <02CHE748>. Aminomethyl substituted allenes have also been used for the synthesis of pyrroles by a palladium catalyzed annulation with aryl iodides <02H(57)2261>. 

Diazines arc formed by the addition of guanidine and its derivatives to diynes in the presence of base, as illustrated by the preparation of 174 from 1,3-hexadiyne and guanidine ... 

Conjugated diynes with a terminal triple bond give products in which the triple bonds remain conjugated as illustrated by the isomerization of 1,3-hexadiyne to... 

Figure 1.10. Structural formula of 5,6-dibromo-l,3-hexadiyne (a) the hexadiyne ending means that the major chain has six carbons and that there are two triple bonds in the chain. Since it is 1,3-hexadiyne, the triple bonds must be between the number 1 and 2 carbons and between the number 3 and 4 carbons, (b) The 5,6-dibromo, of course, indicates two bromine atoms, one each bonded to the number 5 and 6 carbons.

The reaction between disubstituted 1,3-diynes such as 5,5-dimethyl-1-tri-methylsilyl-l,3-hexadiyne with metallocenes M(t -C5H5)2 studied by Baumann et al yielded a complex with the intact diyne when M = Ti and a CT,7c-alkynyl-bridged dinuclear complex when M = Zr. These two types of compounds could be easily discriminated by the use of 7hc couplings observed between the terminal carbon atoms of the 1,3-diyne moiety and the protons either of the t-Bu or the SiMes group. 

Naphthyl substituent shows a different character in the excited state in comparison with phenyl substituent. The photohydration of 1-phenyl-5,5-dim-ethyl-l,3-hexadiyne gives three photohydration products (58-60) (two acetylenyl ketone and one allenyl ketone) through both Si and Tj excited states (Scheme 20). An allenyl ketone product is obtained as a minor product. A proposed mechanism involves the protonation step as the rate limiting step in the formation of acetylenyl ketone products. On the other hand, the allenyl ketone product is formed by the synchronous addition mechanism of H3O+. 

Irradiation of l-(p-nitrophenyl)-5,5-dimethyl-l,3-hexadiyne (p-NDHD) in aqueous sulfuric acid gives four photoproducts (61-64) as shown in Scheme 21 [76]. Kinetic studies on the products formation are carried out monitoring the disappearance rate of the starting material. The data clearly show that p-NDHD is initially converted photochemically into allenyl ketone compounds which undergo thermal hydration to give dicarbonyl compounds. 

Draw the structure of 1,3-cyclopentadiene, of 3-ethyl-l,5-hexadi-ene, and of 6-bromo-l,3-hexadiyne. 

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