Acetylene-terminated phenyl

A family of acetylene-terminated phenyl quinoxalines have been synthesized by the Polymer Branch of the Materials Laboratory. ( 1) These phenyl quinoxalines are remarkable for their thermooxidative stability and resistance to moisture. These materials have potential for structural applications as adhesives or composite matrix resins.(2) The feature of moisture resistance makes the materials especially attractive for bonding aluminum. However, problems arise from the fact that aircraft aluminum alloys (and their surface oxiges) are altered by exposures to temperatures above 177 C (350 F) and this is much lower than the polymerization temperatures of the acetylene-terminated oligomers. 

Progress has been made in initiating the polymerization reaction of an acetylene terminated phenyl quinoxaline at lower temperatures. While this result in itself is of practical significance to the Air Force, the investigation was embellished to provide generic foundations for subsequent studies. Observations were also made that may be of interest to other investigators. 

The Fukuyama indole synthesis involving radical cyclization of 2-alkenylisocyanides was extended by the author to allow preparation of2,3-disubstituted derivatives <00S429>. In this process, radical cyclization of 2-isocyanocinnamate (119) yields the 2-stannylindole 120, which upon treatment with iodine is converted into the 2-iodoindole 121. These N-unprotected 2-iodoindoles can then undergo a variety of palladium-catalyzed coupling reactions such as reaction with terminal acetylenes, terminal olefins, carbonylation and Suzuki coupling with phenyl borate to furnish the corresponding 2,3-disubstituted indoles. 

Interestingly, after reaching the maximum at the 6-membered cycle, the yields drop again. This decrease in efficiency occurs despite the appreciable reduction in the distance between the terminal acetylenic carbons relative to the 6-membered analogue. Here, the efficiency may simply be a function of how photochemical excitation is distributed in the reactive excited state. Calculated enediyne geometries suggest the cyclization is more efficient for those enediynes where the terminal phenyl groups are rotated outside of the enediyne plane (Table 3). 

The Michael addition reaction of dimercaptodiphenylether with N-(3-ethynyl phenyl) maleimide allowed the synthesis of ethynyl-terminated imido-thioether as shown in Fig. 50 (139). This acetylene terminated imidothioether was blended with acetylene terminated polyarylene ether oligomers of different molecular weights and tested as composite resins (140). Blends of functionalized thermoplastics such as the acetylene terminated polyarylene ethers with brittle high-Tg imide resins are finding increased attention for tough high-Tg composites. 

In the presence of a catalytic amount of PdCh, Ar>,BiX2 (X=C1, OAc) couples with arylstannanes to give biaryls (Scheme 14.155) or, under a CO atmosphere, diaryl ketones (Scheme 14.156) [316]. Unsymmetrical biaryls are also prepared by Pd-catalyzed reaction of diaryliodonium salts with Ar3BiX2 [317]. Terminal acetylenes are phenylated by Ph3BiF2 under CuCl catalysis to afford phenyl-substituted acetylenes [318]. 

Murphy et al. [73] studied the cure and degradation of an acetylene-terminated N-labelled poly(imide) using N CPMAS NMR. Initially, the conversion of the amic acid to the imide precursor was followed. Four resolved peaks are observed due to amide and imide either attached to a phenyl ring or at the terminal position. Measurements of the rate of crosspolarization, and the dipolar dephasing experiment, assisted in the assignment to the spectra. Very different rates of cross-polarization (1/Tnh), and values of Ti, were measured for the various structures. Imidization was incomplete after heating to 670 K for 1 h, a result at variance with the results of... 

The insertion of alkynes into Os-H bonds produces vinyl complexes. For example, 0sH(02CCF3)(CO)(PPh3)2 reacts with PhC=CR (R = Me, Ph) to give Os C(Ph)=CHR (02CCF3)(C0)(PPh3)2. These complexes are catalysts for the oligomerization of phenyl acetylene. Terminal alkynes insert into the Os-H bond of OsHCl(CO)(P Pr3)2 to give Os(CH=CHR)Cl(CO)(P Pr3)2. This complex is coordina-tively unsaturated see Coordinative Saturation Unsaturation) and can react with CO to form the six-coordinate complex Os(CH=CHR)Cl(CO)2(P Pr3)2 (Scheme 2). 

Terminal phenyl acetylenes and phenylpropiolic acids couple with vinyl halides in water at 100 °C in the presence of a Cul catalyst, PPh3, K2CO3, and (Bu)4NAc forming 1,3 enynes in yields usually between 50 and >99%P The reactions were successful with both electron-donating and electron-withdrawing meta- and para-substituents on the phenyl acetylenes and vinyl halides Z-vinyl halides did not react. Turnover rates of nearly 10 were observed and a possible mechanism is suggested. 

FIGURE 26.22 Phenyl acetylene-terminated poly(carborane-silane) (PACS) polymer. 

Quan, Z. Zuju, M. Lizhong, N. Jianding, C. 2007. Novel phenyl acetylene terminated poly(carborane-silane) Synthesis, characterization, and thermal property. J. Appl. Polym. ScL, 104 2498-2503. 

N-Aryl analogs have been synthesized193 by cycloaddition of terminal-acetylenic sugar derivatives to azides, as exemplified by the conversion of the pentyne derivative 171a into l-phenyl-4-(D-threo-... 

B-Bromo and B-iodo-9-borabicyclo[3.3.1]nonane add similarly in a cis fashion to terminal triple bonds 471 They do not react, however, with alkenes and internal acetylenic bonds. In contrast to the results mentioned above, phenyl-substituted chloroboranes (PhBCl2, Ph2BCl) do not participate in haloboration. Instead, the C—B bond adds across the multiple bond to form phenylalkyl-(alkenyl) boranes.466,468... 

These are good dienophiles. and aryl vinyl sulfones have found use as equivalents of ethylene and ketene through functional modifications of their adducts. However, as the base-induced elimination of a sulfinic acid to yield an olefin occurs only with difficulty, they are not direct precursors of acetylene equivalents, unless suitably modified as in ( )-l-phenyl-sulfonyl-2-trimethylsilyl ethylene (PhS02-CH=CH-TMS). In its cycloadducts the elimination to an alkene is smoothly realized by the fluoride ion. If an alkylation step is previously carried out on the adduct, the overall process realizes an indirect addition of a terminal acetylene, as in the examples given here [533]. 

Over the last few years it has become clear that rhodium(II) acetate is more effective than the copper catalysts in generating cyclopropenes.12 126 As shown in Scheme 28,12S a range of functionality, including terminal alkynes, can be tolerated in the reaction with methyl diazoacetate. Reactions with phenyl-acetylene and ethoxyacetylene were unsuccessful, however, because the alkyne polymerized under the reaction conditions. 

Electrophilic addition of iodine(III) reagents to the triple bond of alkynes leading to alkenyl(phenyl)iodonium salts is also possible. It has been effected in some alkynes, including acetylene, with Phl+F TfO" [95] or PhI+OH TfO [129] or Phi and XeF2 in MeS03H [130] to afford 2- -trifyloxy-alkenyl(phenyl)iodo-nium salts. Terminal alkynes reacted with p-TolylIF2 in Et3N-5HF to afford similarly jS-E-fluoroalkenyl(phenyl)iodonium fluorides (Scheme 43) [131]. 

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