Octa-2,6-diyne

Di- and tetraynes with hydrogen sulfide in an alkaline medium at 20-80°C form systems containing linked thiophene cycles. Thus, l,4-dithienylbuta-l,3-diyne (47) forms 2,5-di(2-thienyl)thiophene (48) in 78% yield, whereas octa-2,4,6-tiiyn-l-ol (49) under the same conditions gives 5-hydroxymethyl-2-prop-1-ynylthiophene (50) in 50% yield (77HOU947). 

Bis(l-boraadamant-2-yl)methane and -ethane <1998IZV728, 2000IZV501, B-2003MI94> are available via allylboron-acetylene condensation from hepta-l,6-diyne and octa-l,7-diyne, respectively. 

Condensation of triallylborane with octa-l,7-diyne (130-140 °C, 3 h) followed by treatment with methanol afforded a mixture of stereoisomeric l,4-bis(3-methoxy-3-borabicyclo[3.3.1]non-6-en-7-yl)butanes 66a and 66b (Scheme 26). Hydroboration of the latter with H3B-THF in THF and heating under reflux for 2 h gave rise to a mixture of racemic bis-l-boraadamantanes 67a and meso-ioim 67b in 94% overall yield. Pure racemate 67a was isolated by crystallization from the reaction mixture (THF) and converted to the pyridine complex 64 whose structure was established by X-ray diffraction analysis. 

Complexes 68 (mp 173 °C) and 69 (mp 114°C) were prepared starting from the reaction between trimethallyl-borane and octa-l,7-diyne (Scheme 27) . 

X-ray structure analysis and topochemical photopolymerization of 2,5-dimethoxyphenyl-and quinone-substituted octa-3,5-diynes. Tetrahedron 2000, 56, 6781-6794. 

Octa-l,7-diyne, Nona-1,8-diyne, and Deca-l -diyne... 

Products arising from propargylic C—C cleavage are not usually formed in solution, and the dialkyne 5 is photochemically inert to radiation of wavelength 254 nm However, cyclo-octa-l,5-diyne does cleave to give butatriene (equation 10), and the extra driving force here comes from the strain in the cyclic compound . 

Presumably the adducts are formed by singlet addition yielding (257) followed by a second addition. [2 + 4]Addition is also encountered yielding the photo-chemically labile 2,3-diphenylnorbornadiene. The irradiation (206 nm, pentane solution, degassed) of cyclo-octa-l,5-diyne at room temperature rapidly gave butatriene as the only product.176... 

Likewise, a,co-diynes can be used in this cycloaddition for instance, octa-l,7-diyne 176 affords the 5,6,7,8-tetrahydroisoquinoline 177 with nitriles ... 

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. ... 

The heat of hydrogenation of octa-l,7-diyne might be expected to be twice that of 1-butyne, which is in effect one half of the molecule. The difference is only 0-6 kcal/mole. The heat of hydrogenation of hexa-l,5-diyne —139-4) compares closely with that found for octa-l,7-diyne, as might reasonably be anticipated. Also, the heat of hydrogenation of dodeca-3,9-diyne (—131 15) is close to that estimated for two moles of 3-hexyne, (ca. —131 6). In octa-l,7-diyne, hexa-l,6-diyne, and dodeca-... 

Reaction is thought to proceed via initial ring-opening of the cyclobutene ring to give a 3,5-diene-l, 7-diyne. In accord with this, octa-3,5-dienc-l,7-diyne is unstable and is rapidly converted, in high yield, into a dimer of benzocyclobutadiene [103]. 

Subsequently partial hydrogenation of trans,trans- and of cw,c/ -2,8-decadiene-4,6-diyne over a Lindlar catalyst resulted in trans- and cw-7,8-dimethyl bicyclo[4.2.0]octa-2,4-diene, respectively (Scheme 9.48). " ... 

Octa-l,7-diene-3,5-diyne hydrogenated with Lindlar catalyst in n-hexane containing quinoline at 24-25° and slightly more than atmospheric Hg-pressure cycloocta-l,3,5-triene. Y 80%. W. Ziegenbein, B. 98, 1427 (1965). 

A mixture of propargyl bromide and tetrahydrofuran added during 45 min. with ice-cooling below 30° to Al and a trace of HgClg in the same solvent, stirring continued 1 hr. at 25-30°, 1,2-dichloro-1,2-diethoxy ethane and tetrahydrofuran added in one portion at 0°, and kept ca. 2 hrs. at 40-50° -> 4,5-diethoxy octa-l,7-diyne. Y 87%. Also the dimethoxy analog s. H.-J. Kabbe, E. Truscheit, and K. Eiter, A. 68A, 14 (1965). 

Another type of SiCaB reaction takes place when 1,6-diynes 543 bearing a basic amine moiety at the 4-position is employed. For example, the reaction of N-benzyl-, A - -hexyl- or 7V-allyldipropargylamine with EtjSiH (1.6 equiv) catalyzed by Rh(acac)(CO)2 at 65 °C and 50 atm of CO gave the correspontog 2-silyl-7-azabicyclo[3.3.0]octa-5,8-dien-3-one 545 as the exclusive product (Scheme 2-84). 

Octa-l,7-diyne treated with CO2 (initial pressure 50 kgcm - at room temp.) in THF at 100° in the presence of 10 mol.% of Ni(0)-catalyst (prepared from Ni(cod)2 2 eqs. l-(2 -pyridyl)-2-(di-A -butylphosphino)ethane) for 20 h - 5,6,7,8-tetrahydro-3/f-2-benzopyran-3-one. Y 68%. Such functionalized tert. phosphines with hard ligand components owe their effectiveness to intramolecular coordination of the pyridyl group to the Ni-atom in a 6-membered chelate. Trialkylphosphine ligands were not effective for terminally unsubst. acetylenes. F.e. and effect on regioselectivity s. T. Tsuda et al., J. Chem. Soc. Chem. Commun. 1989, 9-10 review of syntheses based on pyridine coordination s. P. Tomasik, L. Brzozka, Wiadom. Chem. 41, 741-57 (1987). 

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