Ethynyl groups terminal

The thermodynamic CH acidity of terminal acetylenes in the series of A-alkylpyrazoles was studied (83IZV466). These equilibrium CH acidity measurements were performed in DMSO by the method of remetallation (75ZOB1529). It reveals some regularities concerning the influence of the ring structure, the nature of other substituents, and the position of the ethynyl group on the acidity of ethynyl pyr azoles. 

Seyferth and coworkers [181] introduced ethynyl groups onto the periphery of carbosilane dendrimers by displacement of chloride from the terminal silicon groups. They further treated these ethynyl terminated silicon dendrimers with Co2(CO)8 to afford the corresponding acetylenedicobalt hexacarbonyl dendritic complexes. 

Although HR-600/Thermid-600 provided promising neat resin and composite properties, major processing problems have plagued these as well as other acetylene-terminated oligomers. Resin flow and wetting is inhibited due to the reaction of the terminal ethynyl groups prior to the formation of a complete melt or soft state. This becomes even more severe due to heat transfer problems as... 

The most successful class of thermally reactive oligomers consists of the functional polymers containing either pendant or terminal triple bonds, especially ethynyl groups. This area of research was recently reviewed (2), and the more recent developments in the field of a,w-bis(ethynylpheny1) aromatic polyether sulfones were summarized in two recent papers (5,6). 

Eastmond, R. Walton, D. R. M. 1968 The protection of terminal ethynyl groups in the oxidative couplings of acetylenes. Chem. Commun. 204—205. 

In many of these applications, the ethynyl group is present in the starting material only in latent form, e.g. as a chlorovinyl substituent, from which it is liberated during the pyrolysis step. That even non-terminal acetylenes can be employed in these cycloaromatizations is illustrated by the protected cross-conjugated diacetylene 43 in Scheme 11. When this was subjected to hydropyrolysis at 900 °C, the diacetylene 44 was generated in situ and double-cyclized to corannulene (40) immediately [23]. 

Oxidative coupling of compounds having two terminal ethynyl groups per molecule has been used for the preparation of polymers, as illustrated by equation (9)... 

The formal elimination of trialkyltin hydrides from enol systems has been very recently devised by Corey and Wollenberg to prepare terminal acetylenes (equation 92) and to introduce the ethynyl group into the -position of a, -unsaturated ketones. As equation (93) shows this may lead to the introduction of an ethynyl group into an angular position d . The preparation of the reagent 31 has been described . 

Three double-bond equivalents which follow from the empirical formula can be confirmed in the NMR spectrum using typical shifts and coupling constants. The proton signal at = 3.05 indicates an ethynyl group with terminal proton an MX system in the alkene shift range with 5m - 4.50 and 5x = 6.30, respectively, and the coupling constants Hz, reveal an ethene... 

Triple bonds can also be selectively reduced to double bonds with diisobutyla-luminum hydride (Dibal-H), ° with activated zinc (see 12-38), with hydrogen and Bi2B-borohydride exchange resin, or (internal triple bonds only) with alkali metals (Na, Li) in hquid ammonia or a low-molecular-weight amine. Terminal alkynes are not reduced by the Na NH3 procedure because they are converted to acetylide ions under these conditions. However, terminal triple bonds can be reduced to double bonds by the addition to the Na—NH3 solution of (NH4)2S04, which liberates the free ethynyl group. The reaction of a terminal alkyne with... 

Other masked ethynyl groups including dihaloethenyls [54b],ethenyl ethers [58] and terminally substituted acetylenes [59] have also been applied in the pyrolytic preparation of PAHs, presumably also via carbene intermediates [60]. Furthermore, the combination of the different synthetic strategies is also possible, as demonstrated by the first successful synthesis of benzocorannulene (28, Scheme 10, [54 g]) and other PAHs. 

A pair of Ullman s nitronyl nitroxide radicals carrying m- and p-ethynylphenyl groups at position 2 of the imidazoline ring (7 and 8) are quite stable at room temperature under air and the unpaired electrons withstand the catalyzed polymerization conditions (see Section 11.4.3) [6]. The terminal ethynyl groups are not susceptible to Pb02 in benzene/metha-nol at room temperature, which is used for the oxidation of the bis(hydroxylamine)s to the nitronyl nitroxides [6, 7]. Fremy s salt gives the best result for the oxidation of the hydroxyl-amine 14 carrying a terminal 1,3-butadiyne moiety [9]. 

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