3-Butyne Subject

Using NaOH as the base, diarylacetylenes have been synthesized from either 2-methyl-3-butyn-2-ol [121] or trimethylsilylacetylene [122], In both cases, NaOH unmasked the protections after the first coupling reaction, revealing the additional terminal alkynyl functionality. Therefore, coupling the adduct 141, derived from 2-iodothiophene and 2-methyl-3-butyn-2-ol, with 2-iodobenzothiophene provided diarylacetylene 142 [121], Analogously, dithienylacetylene (143) was obtained when 2-iodothiophene and trimethylsilylacetylene were subjected to the same conditions [122],... 

CYCLOHEXEN-l-ONE. Importantly, only 1.6 equivalents of Ag20 are required for efficient coupling. The final preparation in this series illustrates the hydrosilation of racemic 3-butyn-2-ol catalyzed by a phosphine based platinum(O) catalyst. The resultant racemic (E)-vinylsilane is then resolved with a commercially available lipase and subjected to a Johnson ortho ester Claisen rearrangement to afford [3R- AND 3S-]-(4E)-METHYL... 

A. ( )-1-(Dimethylphenylsilyl)-1-buten-3-ol (2a). A solution of 10.0 g (0.143 mol) of racemic 3-butyn-2-ol (Note 1) dissolved in 255 mL of tetrahydrofuran (THF, Note 2) in a 1-L, round-bottomed flask equipped with a reflux condenser and nitrogen atmosphere is prepared. Dimethylphenylsilane (21.4 g, 0.157 mol) (Note 3) and a small piece of sodium metal (ca. 5 mg) (Note 4) are placed in the reaction mixture. The solution is stirred for 15 min and 12 mg (2.05 x 10 5 mol) of bis(q-divinyltetramethyldisiloxane)tri-tert-butylphosphineplatinum(O) (Note 5) is added. The reaction mixture is then heated under reflux for 12 hr. The orange solution is cooled to ambient temperature, and the solvent is removed under reduced pressure to yield a crude orange residue containing 2a. The oil is subjected to column chromatography on silica gel (Note 6) (gradient elution 5, 10, 20, 35% EtOAc/hexanes) providing 25.4 g (123.23 mmol, 86%) of pure 2a as a yellow oil (Note 7). 

When 2-methyl-3-butyn-2-ol 66 is subjected to the conditions similar to Equation (34), /3-lactone 205 (SiR3 = SiPhMe2) and 3-silylpropenal 67a are obtained in 43% and 52% yields, respectively (Equation (35))." ... 

Truce and collaborators (7-9) have shown that cis-dichloroethylene 20 reacts readily with sodium -toluenethiolate in the presence of sodium ethoxide to give cis-1,2-bis-p-tolylmercapto-ethylene 22 while the trans-isomer 21, when subjected to the same conditions is recovered unchanged. Convincing evidence was obtained that the conversion 20 22 takes place via the intermediates 23, 24, and 25. Truce and Simms (9) have also observed that the base-catalyzed addition of -toluenethiol to phenyl acetylene and to 2-butyne yields ci s-styryl -tolylsulfide (26) and 2-p-tolylmercapto-trans-2-butene (27) respectively. 

Each of the dibromides shown yields 3,3-dimethyl-1-butyne when subjected to double dehydro-halogenation with strong base. 

To a solution of 2-iodo-5-(4-fluorophenylmethyl)thiophene (5.30 g, 16.6 mmol), in anhydrous DMF (5.0 ml) was added (R)-N-hydroxy-N-(3-butyn-2-yl)urea (2.12 g, 16.6 mmol), triphenylphosphine (84.0 mg, 0.32 mmol), bis(acetonitrile)palladium(II) chloride (40.0 mg, 0.16 mmol), copper(I) iodide (16.0 mg, 0.08 mmol), and diethylamine (5.6 ml). The mixture was stirred under nitrogen at room temperature for 22 h and concentrated in vacuum at 32°C. The residue was subjected to chromatography on silica eluting with 2-7% MeOH in CH2CI2, crystallization from ethyl acetate-hexane and trituration in CH2CI2 to afford (R)-N- 3-[5-(4-fluorophenylmethyl)thien-2-yl]-l-methyl-2-propynylVN-hydroxyurea as a cream-colored solid 0.94 g (18%), melting point 135°-136°C, (dec). 

In an alternative route to such molecules, Cargill and Crawford demonstrated that the photocycloadduct of cicyclo[4.3.0]non-l(6)-en-2-one (474) and 2-butyne, ie., 475, was subjected to acid-catalyzed isomerization with formation of 476.409)... 

A high-molecular-weight, insoluble polymer is obtained when perfluoro-2-butyne is subjected to various initiators for free-radical polymerisation (Figure 7.87). The off-white colour of this material is remarkable for a polyacetylene [307, 308]. Indeed, it is largely ignored in discussions on polyacetylenes because, of course, the fact that it is not coloured also means that the system is not conjugated the trifluoromethyl groups keep the TT-systems out of plane relative to each other. 

Acetylenes are well known to undergo facile trimerizations to derivatives of benzene in the presence of various transition metal catalysts 23). A number of mechanisms for this process have been considered including the intervention of metal-cyclobutadiene complexes 24). This chemistry, however, was subjected to close examination by Whitesides and Ehmann, who found no evidence for species with cyclobutadiene symmetry 25). Cyclotrimeri-zation of 2-butyne-l,l,l-d3 was studied using chromium(III), cobalt(II), cobalt(O), nickel(O), and titanium complexes. The absence of 1,2,3-trimethyl-4,5,6-tri(methyl-d3) benzene in the benzene products ruled out the intermediacy of cyclobutadiene-metal complexes in the formation of the benzene derivatives. The unusual stability of cyclobutadiene-metal complexes, however, makes them dubious candidates for intermediates in this chemistry. Once formed, it is doubtful that they would undergo sufficiently facile cycloaddition with acetylenes to constitute intermediates along a catalytic route to trimers. 

Bayer and Siebert reported the reaction of 3,3-dimethyl-l-butyne with -BuLi in pentane, followed by the addition of boron trichloride to afford the intermediate dichloro(3,3-dimethylbut-l-ynyl)borane that was hydroborated with dichloroborane formed in situ to give l,l-bis(dichloroboryl)-3,3-dimethylbutene 51 (Scheme 6) <2002ZN1125>. When the latter was subjected to halogen exchange with boron triiodide, it was converted into the corresponding tetraiodide 52, which underwent a redox reaction with hex-3-yne to give the 2-(2,2-dimethylpropylidene)-l,3-diborole 22 in 73% yield. 

Boron is the prime metal in the area of stoichiometric interactions between metals and unsaturated bonds. Especially, boron hydride additions have been investigated, in particular by H. C. Brown and his students. Nowadays, these addition reactions are well-established text book subjects. A number of reviews on hydroboration have appeared . The development of a clear mechanistic picture lagged far behind the applications in synthesis. It was also the group of Brown that contributed to mechanistic understanding by performing careful kinetic measurements using 9-borabicyclo[3.3.1]nonane, abbreviated as 9-BBN-H, as reagent. Reactive alkynes such as 1-hexyne and 3-methyl-1-butyne exhibited first-order kinetics in 9-BBN-H with a rate constant equal to that of reactive... 

Reduction of the lactone 137 to the corresponding lactol 138 necessitated use of DIBAL quenching the reaction with methanol followed by workup with aqueous potassium sodium tartarate furnished the product as a clear viscous oil that solidified on standing to a white solid. The anomeric hydroxyl group was conveniently protected by the formation of terf-butyldimethylsilyl ether by treatment with rert-butyldimeth-ylsilyl chloride, imidazole, and A,A-dimethylaminopyridine. Further activation of the anomeric position in compound 139 with trimethylsilyl bronfide followed by treatment with l-t-butyldimethysiloxy-3-butyne and n-butyUithium yielded a transicis mixture (1 1) (140) that was used without further purification. Reaction of compound 140 with tetrabutylammonium fluoride led to deprotection of the hydroxy functionality. The resulting transicis mixture of the alkynols was subjected to extensive chromatography and repeated crystallization to obtain a tran -alcohol (141) as a white crystalline solid. Further elaboration to 131 was carried out by appropriate modifications of a literature procedure. ... 

The Diels-Alder adduct formed by treating furan with hexafluorobut-2-yne has been subjected to a retro-Diels-Alder reaction acetylene is eliminated and the reaction provides a route to 3,4-bis(trifluoromethyl)furan. The corresponding cycloadduct (154) formed from l,l-dimethyl-2,5-diphenyl-sllacyclopentadiene and the butyne was decomposed in an attempt to generate dimethylsilylene by a symmetry-allowed cheletropic fragmentation (Scheme 50) 836 evidence for silylene formation could be obtained unless the decomposition was effected photochemically or in refluxing cumene, under which conditions the addition of tolan enabled dimethylsilylene to be trapped... 

Rzaeva et al." compared propargyl ether, propargyloxy formates, and propar-gyloxy acetates, and found them all to be effective inhibitors of steel in HCI. Allabergenov et al." synthesized various propargyl ethers of substituted phenols, which also proved to be quite effective (18% HCI at 160°F, i.e., 71°C). One such product, 1-phenoxy-2-butyn-4-ol, is so exceptional that it has been the subject of subsequent studies."... 

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