1-Phenyl-l-alkyne

The organozinc reagents 123, which were generated from 1-phenyl-l-alkyne 122 with nBuLi in the presence of 1.5 mol% of HgCl2 followed by addition of 1.5 equiv. of ZnBr2, exists as a tautomeric mixture of an allenylzinc and a propargylzinc species (Scheme 3.62) [103]. 

The mechanism of the Au(III) catalysis proposed in Scheme 5 implies the stereoselective formation of the new C-C bond which, of course, cannot be observed in the final product when terminal alkynes are used (the aryl group and the former alkyne hydrogen are situated at the same side of the double bond in the vinyl-Au intermediate). For the reaction of 1-phenyl-l-propyne and mesitylene 1 (see below, Table 1) the proposed mechanism should lead to preferential formation of the Z isomer which is, in fact, observed [2]. The formation of a small amount of E isomers can be explained by isomerization of the initially formed Z compound. Such isomerization was, in fact, observed directly in the case of related electron-poor alkynes [4],... 

Phenyl-1-alkynes (1-phenyl-l-propyne, -1-butyne, and -1-nonyne) polymerize in high yields in the presence of WClg—Pl Sn 30,32). The Mw s of the polymers, however, are not very high (5x 103-5x 104). MoCls—Ph4Sn is virtually inactive toward these acetylenes. 

Many monomers with simple structures, including phenylacetylene, t-butyl-acetylene, 1-phenyl-1-propyne, 2-octyne, and 1-trimethylsilyl-l-propyne, are commercially available. These monomers are usually purified by distillation in the presence of suitable drying agents prior to use. On the other hand, monomers that are more complex, such as ort/zo-substituted phenylacetylenes, A-pro-pargylcarbamates, ring-substituted diphenylacetylenes, and 1-chloro-l-alkynes, must be synthesized. Derivatization of simple alkynes rather than formation of the acetylenic moiety, is frequently applied to synthesize such monomers. These are then purified by vacuum distillation or column chromatography. 

Substituted 1-halo and 1-alkoxy isoquinolines are formed from A/-methoxy benzimidoyl halides and alkynes with a ruthenium catalyst (Scheme 59) (13CC3703). The reaction with an unsymmetrical alkyne, 1-phenyl-l-propyne, occurs regioselectively, with the phenyl adding adjacent to the nitrogen. The reaction occurs with both imidoyl chlorides and... 

Alkynes (e.g., 2-octyne), which are sterically not very crowded, polymerize with Mo catalysts to give polymers with MWs over one million. For these monomers, W and Nb catalysts are less effective, and Ta catalysts yield only cyclotrimers. Symmetrical dialkylacetylenes (e.g., 4-octyne) are slightly more crowded, and consequently Nb, Ta, and W catalysts exhibit high aaivity, while Mo catalysts are hardly active. Since f-phenyl-l-alkynes (e.g., 1-phenyl-1-propyne) possess even larger steric effeas, Nb and Ta catalysts produce polymers having MW equal to 1 X 10 -1 X 10 . By contrast, W catalysts yield only oligomers of MW lower than 1 x 10, and Mo catalysts are inaaive. 

DPAs and 1-phenyl-1-alkynes show intense photo- and electroluminescences. A systematic investigation of the luminescence of poly(DPA)s has revealed that these polymers exhibit photoluminescence around 530 nm and electroluminescence around 550 nm. In a similar way, poly(l-phenyl-l-alkyne)s photochemically and electrochemically emit strong lights with spectral maxima located around 455 and 470 nm, respectively. Green and blue emissions are observed from electroluminescent devices using poly(DPA)s and poly(l-phenyl-1-alkyne) s, respectively, as emission layers. - "... 

When compound (443), which contains alkene and alkyne moieties, was reacted with benzonitrile oxide, both an isoxazoline (444) and isoxazole (445) were produced, with the former predominating. Oxidation of (444) with permanganate produced 3-phenyl-2-isoxazoline-5-carboxylic acid (446) (67ZOR82i). The reaction of 1-trimethylsilylbut-l-yne-3-ene produced only a compound which reacted at the alkenic unit. Oxidation of the adduct also produced (446) (68ZOB1820). These reactions are shown in Scheme 102. 

The regiochemistry of Al-H addition to unsymmetrically substituted alkynes can be significantly altered by the presence of a catalyst. This was first shown by Eisch and Foxton in the nickel-catalyzed hydroalumination of several disubstituted acetylenes [26, 32]. For example, the product of the uncatalyzed reaction of 1-phenyl-propyne (75) with BujAlH was exclusively ds-[3-methylstyrene (76). Quenching the intermediate organoaluminum compounds with DjO revealed a regioselectivity of 82 18. In the nickel-catalyzed reaction, cis-P-methylstyrene was also the major product (66%), but it was accompanied by 22% of n-propylbenzene (78) and 6% of (E,E)-2,3-dimethyl-l,4-diphenyl-l,3-butadiene (77). The selectivity of Al-H addition was again studied by deuterolytic workup a ratio of 76a 76b = 56 44 was found in this case. Hydroalumination of other unsymmetrical alkynes also showed a decrease in the regioselectivity in the presence of a nickel catalyst (Scheme 2-22). 

This appears to be the first report of the addition of H2 to the silylformyla-tion reaction mixture. Good yields are obtained when Et3SiH or PhjSiH is used in the reaction of 1-hexyne or 4-phenyl-l-butyne. Although a variety of functionally substitued terminal alkynes have been studied, most lead only to the silylformylation product and do not appear to be affected by the presence of H2 in the system. Other rhodium catalysts investigated, such as [Rh(COD)(dppb)]+BPh4 and Rh6(CO)16, catalyze the silylformylation reaction even under H2 pressure and do not lead to any of the silylhydrofor-mylated products. 

As l,2,4-triazole-3,5-dione (PTAD) is a stronger dienophile than acetylenic esters, more facile formation of the Diels-Alder cycloadducts was expected. But because it cannot behave as a diene in a reaction with alkynes such as diethyl azodicarboxylate, the formation of dihydrooxadia-zines is excluded. In spite of these characteristics, no Diels-Alder adducts were obtained in the reaction of l-phenyl-4-vinylpyrazole with PTAD in acetone at -80°C and 2,2-dimethyl-4(l-phenylpyrazol-4-yl)-8-phenyl-l,6,8-triaza-3-oxabicyclo[4.3.0]nona-7,9-dione 277 was obtained as a major product. The isolation of the tetrahydrooxadiazine 277 indicates that the 1,4-dipole 278 was formed and trapped with acetone. 

The photoaddition of alkanes onto electron-poor alkynes (e.g., propiolate or acetilendicarboxylate esters) can be accomplished by a radical conjugate addition reaction [7]. Radicals have been generated either via hydrogen abstraction from cycloalkanes or via electron transfer from 2-alkyl-2-phenyl-l,3-dioxolanes. In the first case, the irradiation was pursued on an alkane solution of an aromatic ketone (used as the photomediator) and the alkyne. Under these conditions, methyl propiolate was alkylated upon irradiation in the presence of 4-trifluoromethylacetophenone to form acrylate 48 in 97% yield (E/Z= 1.3 1 Scheme 3.31) [78]. 

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