Ethynyl groups

Examination of the material recovered from the mother liquors indicates that the ethynyl group is reduced in about 10% of the starting material. 

The partial hydrogenation of a 17-ethynyl group over deactivated palladium occurs more readily than the saturation of any other functional group. This is also true of 17-ethynyl carbinols and 17-acetylenic ethers (52). ... 

The 13-ethyl-17-ketones, i.e., (63), have been found to be considerably less reactive than their 13-methyl counterparts towards acetylenic nucleophiles. The difference is attributed to the additional steric hindrance provided by the ethyl group. An attempt to introduce an ethynyl group into mc- 2>-isopropyl-3-methoxygona-l,3,5(10)-trien-17-one was unsuccessful even in ethylenediamine at 50°. However ethynylation of rac-13-isopropyl-3-methoxygona-1,3,5(10),8(14)-tetraen-17-one proceeded smoothly at room temperature to afford the 17a-ethynyl compound in 60% yield. ... 

Oligopyridine two-dimensional ligands connected by alkyne spacers with 1-4 ethynyl groups as photoactive conductors of molecular size 96CC1707. 

The pyrolysis of 1-propynoylpyrazoles gives alkynylpyrazoles (85TL6373 94AJC991). The peeuliarity of these eompounds is that the ethynyl group is bound to nitrogen atoms. Flash vaeuum pyrolysis (EVP) of 1-propynoylpyrazole at 700-900°C/0.1 torr gives 1-ethynylpyrazole in low yield (Seheme 58). 

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. 

The acidity of 4-ethynyl- 1-methylpyrazole is lower than that of phenylacetylene (pK =29.1) [75IZV2351 79JCS(P2)726 84IZV923]. The ethynyl group in other positions of pyrazoles has smaller values i.e., 4-pyrazolyl radicals have a weaker electron-acceptor characteristic than the phenyl ring. 

In the 4-substituted 1,3-dimethylpyrazoles with ethynyl group fixed in position 5, the acidity increases with a change in the character of substituents in the series H = NH2 < C CPh < I < Br = Cl. 

The increasing CH acidity in the ethynylpyrazole series points to the advantageous inductive nature of this influence. Although the data are rather scarce, some correlation is observed between the ethynyl group values and (T constants of substituents in heterocycles (Fig. 3). 

Fig. 3. The ethynyl group pA a values and

Replacement of the para-substituted phenyl unit of alternating phosphine-ary-lene polymers by an ethynyl group, gives rise to a new family of 71-conjugated materials. Indeed, compounds (77) and (78) were prepared in 53% and 3% iso-... 

Fig. 3. Known and hitherto elusive perethynylated building blocks for two- and three-dimensional acetylenic scaffolding. The only compounds shown are those with either free or silyl-protected ethynyl groups...

In order to connect ethynyl groups to the cyclobutadiene or cymantrene unit, we... 

Analogous reactions were postulated to occur for 17a-ethynylestradiol and, on the basis of experiments with model compounds, oxidation of the ethynyl group to -COCHO (Huber et al. 2004). 

The vinyl substituents could be converted by bromination and dehydrobromination to pendant ethynyl groups. 

Elaboration of a commercially viable route for total synthesis of 19-nor steroids led to the introduction of the totally synthetic product norgestrel (71) as the progestational component of an oral contraceptive. As was observed in the "natural" 19-nor-compounds, reduction of the 17-ethynyl group to 17-ethyl affords compounds with androgenic/anabolic... 

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. 

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