Penta-l,3-diyne

The reaction of diacetylene and its asymmetric homologs (penta-l,3-diyne, hexa-1,3-diyne) with semicarbazide (72ZOR2605) affords the amides of 3-methyl-pyrazole- 1-carboxylic acid (27) (80°C, EtONa, EtOH, 40 h). Amide 26 undergoes irreversible rearrangement to amide 27 at 80°C (EtONa, EtOH). 

In the majority of pentatetraenylidene complexes prepared or generated so far, the pentatetraenylidene ligand is derived from suitable C5 precursors. Usually penta-1,3-diynyl derivatives like the alcohol HC = C—C = C—CPh20H, its trimethylsilyl ether, or the 5,5,5-tris(dimethylamino)-substituted penta-l,3-diyne are employed. 

Scheme 3.13 Allenylidene complexes from pentatetraenylidene ruthenium complexes formed in situ by reaction of [RuCl2(dppm)2] and penta-l,3-diyne derivatives.

Finally, anions produced by deprotonation of an alkyne a to the triple bond can also be added to carbon disulfide. This can produce 2-(methylthio)thiophenes via the sequence shown in Scheme 85 or can be extrapolated (Scheme 86) [132] to penta-l,3-diynes and lead to thieno[2,3-b]thiophenes 61. 

Scheme 86 The synthesis of thieno[2,3- >]thiophenes from penta-l,3-diynes [132]...

Photoinduced absorption studies of the oligomer have shown that the dominant long-lived photocarriers are bipolarons formed by interchain charge separation. The lifetimes of the bipolarons in poly(l-(A-carbazo-lyl)penta-5-acetoxy-l,3-diyn) are of the order of seconds at 80 K. The polymer of 1-(A-carbazolyl)-penta-l,3-diyne-5-ol, which is an intermediate compound in the synthesis of (61), has a very low band gap energy (1.6 eV) exhibits a strong non-linear optical... 

The attempts to apply both of the above-described reactions for the preparation of the parent heterocycle 22 (R1 = R2 = H) with the use of penta-l,4-diyn-3-one were only partially successful. The yields of 22 (R1 = R2 = H) were lower than 5%, the main products being unidentified oligomers (92MI3). The first synthesis of 22 (R1 = R2 = H) of preparative significance was when l,5-bis(trimethylsilyl)penta-l,4-diyn-3-one was the... 

The addition of telluride anion to l-(trimethylsilyl)penta-l, 4-diyn-3-ones apparently represents a general method for the preparation of 2-substituted l-telluracyclohexa-2,5-dien-4-ones 22 (92MI3). In actual fact, the reaction of l-(trimethylsilyl)-5-phenylpenta-l,4-diyn-3-one with telluride anion affords 22 (R1 = Ph, R2 = H) in 38% yield, whereas only 12% of this compound is attained in the reaction with l-phenylpenta-l,4-diyn-3-one (87JOC3662). 

Penta-l -diyne (Methyldiacetylene). CH3.C C.CiCH mw 65.10 OB to COj -294.93% liq mp -4.5 to -38.5° bp 76-77° (explds at atm press), 45° at 140mm d 0.7909 g/cc at 20/4° RI 1.4762 (Ref 3) and 1.4817 (Ref 1). Sol in ethanol and petr with a bp > 180°. Prepn is by reacting monosodium-acetylenide with dichloromethane in liq ammonia at 20 to 40°, followed by treatment with ammonium chloride. The product is stable in the dark at —35° but polymerizes readily at above —20° in the light. Penta-1,3-diyne forms two expl salts Copper penta-1,3-diyne, CuCsH3, dark yel ndls, by reaction with CuCl, explds on shock or by rubbing and Silver penta-1,3-diyne, yel-brn ndls, by reaction with aq silver nitrate in ammonium hydroxide, a v expl compd Refs 1) Belli, [247], 1057 <1117>... 

Finally, silylated penta-3,4-dien-l-ynes (216) are synthesized from 1,5,5,5-tetra-lithiopenta-l,3-diyne (215) with Me3SiCl in THF at very low temperature (equation 102)128. 

Another unsymmetrical polydiacetylene with the carbazolyl group as one of the substituents was prepared by Dellepiane et al. [386,387]. Since the polymerizability of monomers with two aromatic groups is usually low, the authors expected increased reactivity from l-(A -carbazolyl)penta-5-acetoxy-l,3-diyn (58). However only oligomers were obtained. 

Dien-4-ynes 136 (R -R = alkyl) are produced from propargylic carbonates 135 and terminal alkynes in the presence of a palladium-phosphine complex and copper(I) iodide. The linear co-dimerization of terminal acetylenes and 1,3-dienes is catalyzed by ruthenium(cyclooctadiene)(cyclooctatriene)(trialkylphosphine) (alkyl = Et, Bu or octyl) thus 1-hexyne and methyl penta-2,4-dienoate give a mixture of the eneynes 137 and 138. Coupling of octa-l,7-diyne (139) with the acetylenic bromo acid 140 in aqueous THF-methanol containing butylamine, hydroxylamine hydrochloride and copper(I) chloride gave a mixture of the triynyl acids 141 and 142. ... 

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