Terminal acetylenic group

The most convenient method of preparing the flexible (low Tg) system is to employ the Ullmann ether reaction of dibromobenzene and aromatic bis-diols followed by catalytic replacement of the bromine atoms by terminal acetylene groups. A host of commercially available bis-diols have been used in the synthesis with both meta and para dibromobenzene. Low Tg arylether oligomers have been prepared containing sulfone, sulfide, carbonyl, isopropyl and perfluoroisopropyl groups in the backbone (9). 

In only one case was the triple bond differently functionalized a terminal acetylene group was converted by hydroboration into a for-mylmethylene (OHC-CH2-) grouping. In this way, 2-deoxy-DL-erythro-pentose (2) was obtained10 from en/t/iro-4-pentyn-l,2,3-triol (1). 

When the terminal acetylenic group was replaced with an olefinic double bond the analogous process gave rise to the stereoselective formation of di-hydropyrido[l,2- ]azepines 98 in a good yield (Scheme 30) (97T14687). 

The propargylic alcohol group may be exploited as an allylic alcohol precursor (Eq. 6A.2) and may be generated by nucleophilic addition to an electrophile [25] or by addition of a formaldehyde equivalent to a preexisting terminal acetylene group [26], Once in place, reduction of the propargylic alcohol with lithium aluminum hydride or, preferably, with sodium bis(2-methoxyethoxy)aluminum hydride (Red-Al) [27] will produce the trans allylic alcohol. Alternately, catalytic reduction over Lindlar catalyst can be used to obtain the cis allylic alcohol [28]. The addition of other lithium acetylides to ketones produces chiral secondary alcohols, which also can be reduced by the preceding methods to the cis or trans allylic alcohols. Additional synthetic approaches to allylic alcohols may be found in the various references cited in this chapter. 

Figure 7-43. The formation of a [3]-catenane. The coupling of the terminal acetylene groups is achieved by reaction with copper salts and dioxygen.

The reaction of the Simmons-Smith reagent with a carbon-carbon triple bond gives cyclopropene and its isomers (72), along with small amounts of allene derivatives (123, 529). Terminal acetylenic groups give... 

In the second approach shown in Scheme 10, the vinyl radical was generated by addition of a tributyltin radical to the terminal acetylene group. In this case, the allyl radical formed in the first cyclization reaction might provide a large steric bias during the second ring closure and could thus impose a better stereoselectivity than in the first approach. The synthesis commenced from the same starting material 77 as in the synthesis of 78. The butenyl chain was attached first and the butynyl chain was introduced second to provide ketoester 83. 

Bauerle and co-workers have synthesized a macrocycle consisting of 8 thiophenes in conjugation by an oxidatively induced elimination of platinum complexes <03CC948>. The platinum complexes 55 were obtained by reaction of terthiophene with terminal acetylenic groups with cw-Pt(dppp)Cl2 in the presence of Cul and EtsN. C-C bond formation was effected by oxidatively induced elimination using iodine and the diacetylene bridged thiophene macrocycle 56 was converted to an all thiophene macrocycle 57 by reacting with sodium sulfide. 

A complex of DBU and copper(I) halide (chloride or iodide) was used for the alkylation of terminal acetylene groups in an inert solvent and in the presence of a small amount of hydroxylamine hydrochloride under an argon atmosphere (75FPR2243172 75GEP2344985 78LA658). 

Sefcik and coworkers [80] were the first to use solid-state NMR to study the curing of poly(imide) oligomers terminated with reactive groups. The authors observed a clearly-resolved peak at 84 ppm in the spectrum of the unreacted poly(imide) resin, Thermid 600, due to terminal acetylene groups. On curing at 450-640 K, the decrease in intensity of this peak allowed facile... 

Protection of a terminal acetylene group. Earborn et al.H found that treatment of the Grignard reagent (1) with trimethylchlorosilane in THF gave (2). Conversion... 

The Infrared spectra exhibited in all cases a sharp band at 3310 cm-- -, indicative of a terminal acetylene group, (4 ) and absorptions attributable to the FEB polymer structure.(5) Absent were absorptions in the 3400-3500 cm- region, indicative of unreacted o-aminophenol and at 1680 cm -, indicative of unreacted imidate ester. A representative infrared spectrum is shown in Figure 1. 

Reactions with butyllithium/tetramethylenediamine Silylacetylenes from halides Protection of terminal acetylene groups as trimethylsilyl derivatives... 

This reaction was first reported by Kuhn and Winterstein in 1928. It is the conversion of adjacent diois into corresponding olefins by means of a diphosphorus tetraiodide reduction and is known as the Kuhn-Winterstein reduction. This reaction is tolerable for the diois with a terminal acetylene group if the experimental conditions are carefully handled, such as the addition of diol in anhydrous pyridine to the supersaturated solution of diphosphorus tetraiodide in carbon disulfide. In most cases, this reaction gives /runs-oleflns as major products, unless the diol group is a part of a ring. ... 

Aromatic polyamides with terminal acetylenic groups were formed from 2,2 -diiodo-diphenyl-4,4 -dicarbonyl chloride reacted with aromatic diamines. The phenylethynyl groups were introduced by reacting the iodine moieties with copper phenyl acetylide. Thermal treatment converted the prepolymers to 9-phenyl dibenzanthracene based rigid-rod polymers that fail to melt below 500... 

The conversion of tertiary alkylacetylenic carbinols with a terminal acetylenic group to predominantly a,p-unsaturated ketones and not the expected aldehydes, is referred to as the Rupe rearrangement ... 

It has been possible to prepare [2]catenanes by simply using neutral n-n stacking interactions. Sanders reported the use of crown ether macrocycle 40 containing two electron-rich naphthalene units, which could interact with 2 equivalents of an electron-poor aromatic diimide unit 41 that is appended with terminal acetylene groups to allow... 

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