5- penta-2,4-diyn

The product is distilled under nitrogen using a 25-cm. Vigreux column (Notes 8 and 9). After removal of unreacted propargyl bromide and phenylacetylene, 1-phenyl-1,4-penta-diyne is collected as the main fraction, b.p. 64-66° (0.45 mm), n25D 1.5713. The yield is 51-64 g. (45-57%) (Notes 9 and 10). The colorless product is best stored under nitrogen at ca. —78°. The n.m.r. spectrum (60 mHz., neat, external tetramethyl-silane reference) shows a triplet at 1.76p.p.m., a doublet centered at 2.92 p.p.m., and a multiplet at 6.87 p.p.m. of relative intensities 1 2 5, respectively (Note 11). 

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). 

Penta-1,3-diyne (Methyldiacetylene). CH3.CiC.CiCH mw 65.10 OB to C02 —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) Beil 1, [247], 1057 <1117)... 

The basic building block for the protected expanded [n]pericyclinones 89 [391 was obtained by simple acetalization of l,5-bis(trimethylsilyl)penta-l,4-diyne-... 

Not only electrophilic 1,4-addition, as shown above, but also radical 1,4-addition to conjugated enynes such as selenosulfonation is known to yield acceptor-substituted allenes [118]. Finally, monotitanation of conjugated diynes followed by treatment with benzaldehyde and aqueous workup leads to an ester of penta-2,3,4-tri-enoic acid, which is formally also a product of 1,4-addition [147]. 

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.

Keywords 5-(2-methylthio-4-methylpyrimidin-5-yl)penta-2,4-diyn-l-ol, polymerization... 

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). 

Competing dissociation and isomerization pathways in energy-selected ions of butene, pentene, 1,4-oxathiane, 1,4-dithiane, and dioxane A —> X Emission spectra of jet-cooled penta-1,3-diyne cations and deuteriated analogues. Vibrational frequencies and spin-orbit splittings A — X Emission spectra of jet-cooled CHjC C—C CCHJ and its [ Hj]- and analogues... 

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. 

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