METAL ACETYLIDES

Both cis- and irans- 1,2-dibromoethylenes react with metal acetylides, but with different reactivity. For the competitive reaction of cis- and trans- fl-dibromoethylenes with the zinc acetylide 314 shows that the irans isomer is more reactive than the cis isomer[228,229]. It was also found by a competitive reaction with the zinc acetylide 317 that the irans vinyl monobromide 315 is more reactive than the cis isomer 316[230]. 

Chlorine Ammonia, acetylene, alcohols, alkanes, benzene, butadiene, carbon disulflde, dibutyl phthalate, ethers, fluorine, glycerol, hydrocarbons, hydrogen, sodium carbide, flnely divided metals, metal acetylides and carbides, nitrogen compounds, nonmetals, nonmetal hydrides, phosphorus compounds, polychlorobi-phenyl, silicones, steel, sulfldes, synthetic rubber, turpentine... 

Hydrogen chloride Acetic anhydride, aluminum, 2-aminoethanol, ammonia, chlorosulfonic acid, ethylenediamine, fluorine, metal acetylides and carbides, oleum, perchloric acid, potassium permanganate, sodium, sulfuric acid... 

Lead(ll) oxide Chlorinated rubber, chlorine, ethylene, fluorine, glycerol, metal acetylides, perchloric acid... 

Metal acetylides Metal-air cells Metal alcoholates Metal alkoxides Metal alloys Metal amalgams... 

Metal Acetylides. The replacement of a hydrogen atom on acetylene by a metal atom under basic conditions results in the formation of metal acetyhdes which react with water in a highly exothermic manner to yield acetylene and the corresponding metal hydroxide. Certain metal acetyUdes can be... 

Difliioramino compounds Fliiorodinitromethyl compounds Haloacetylene derivatives Halogen azides High-nitrogen compounds Hydroxylammoniiim salts Metal acetylides... 

Ethynylation of the totally synthetic racemic 18-methyl-17-ketone (63) with acetylene and potassium t-butoxide in t-butanol-toluene or with alkali metal acetylide in liquid ammonia gives a low yield of rac-18-methyl-17a-ethynyl-3-methoxyestra-l,3,5(10)-trien-17/ -ol (64). 

Alkali metal acetylides M2C2, MCCH and MCCR can readily be prepared by passing C2H2 or C2HR into solutions of the alkali metal in liquid NH3, and these can be used to synthesize a wide range of transition-element... 

Luminescent polynuclear metal acetylides whith a metal as part of a cycle 99JOM(578)3. 

Reaction of estrone with a metal acetylide affords 17a-ethynyl-173-hydroxy-estradiol (etbynylestradiol, 30a EE). This compound is equipotent with estradiol by subcutaneous administration, but it is 15 to 20 times as active when administered orally. Ethynylation of the methyl ether of estradiol analogously affords mestranol (30b), It should be noted that the same factors apply in these reactions as in previously discussed reductions at 17 almost the sole products of these reactions are those which result from attack of reagent from the least hindered a side of the steroid. Ethynylestradiol and mestranol are of special commercial significance since the majority of the oral contraceptives now on sale incorporate one or the other of the compounds as the estrogenic component. 

Oppenauer oxidation of the enol ether (34) affords the corresponding 17 ketone (37) (the enol ether is stable to the basic oxidation conditions). This ketone affords the corresponding 17a-ethynyl compound on reaction with metal acetylides. Hydrolysis of the enol ether under mild conditions leads directly... 

Especially in the early steps of the synthesis of a complex molecule, there are plenty of examples in which epoxides are allowed to react with organometallic reagents. In particular, treatment of enantiomerically pure terminal epoxides with alkyl-, alkenyl-, or aryl-Grignard reagents in the presence of catalytic amounts of a copper salt, corresponding cuprates, or metal acetylides via alanate chemistry, provides a general route to optically active substituted alcohols useful as valuable building blocks in complex syntheses. 

We see from these examples that many of the carbon nucleophiles we encountered in Chapter 10 are also nucleophiles toward aldehydes and ketones (cf. Reactions 10-104-10-108 and 10-110). As we saw in Chapter 10, the initial products in many of these cases can be converted by relatively simple procedures (hydrolysis, reduction, decarboxylation, etc.) to various other products. In the reaction with terminal acetylenes, sodium acetylides are the most common reagents (when they are used, the reaction is often called the Nef reaction), but lithium, magnesium, and other metallic acetylides have also been used. A particularly convenient reagent is lithium acetylide-ethylenediamine complex, a stable, free-flowing powder that is commercially available. Alternatively, the substrate may be treated with the alkyne itself in the presence of a base, so that the acetylide is generated in situ. This procedure is called the Favorskii reaction, not to be confused with the Favorskii rearrangement (18-7). ... 

Acetylene can form metal acetylides, e.g. copper or silver acetylide, which on drying become highly explosive service materials require careful selection. 

Keywords. Metallodendrimer, Organometallic complex. Metal acetylide... 

The alkynyl-metal (metal-acetyhde) complex is one of the best building blocks for organometallic dendrimers, since it has some advantages compared to other organometallic complexes [18]. Most of the metal-acetylide complexes are thermally robust and stable, even when exposed to air and moisture. Metal-acetylide complexes are fairly accessible in high yields by well-established synthetic methodology [19]. These features are essential to the construction of dendrimers. 

Metal-acetylide complexes have been used as a unit of organometallic polymers that have metallic species in the main chain [20]. Representative examples are metal-poly(yne) polymers (19) of group 10 metals depicted in Scheme 5. These polymers are easily prepared from M(PR3)2Cl2 (M=Pt, Pd) and dialkynyl compounds catalyzed by Cu(I) salts in amine. Recently, this synthetic method was successfully applied to the construction of metal-acetylide dendrimers. 

Metal-acetylide complexes including metal-poly(yne) polymers often show unique properties [21-23]. Thus, metal-acetylide dendrimers are of interest because amplification of the functionality due to metal-acetylide units based on three-dimensional assembly with a regular dendritic structure is expected. 

Scheme 12. Reversible formation of cationic metal-acetylide dendrimers 39 and 40...

The effect of ethylmagnesium iodide on ethoxyacetylene leads to a metal acetylide, which detonate when the medium is stirred. 

Propargyl bromide forms explosive metal acetylides when copper or its alloys, silver or mercury are present. 

Because of the slightly acidic nature of the sp C-H bonds, the reaction of metal acetylides with various electrophiles is one of the most general strategies in organic transformations.1 Traditionally, such reactions are carried out by using alkali metal acetylides which are air and water sensitive. On the other hand, there is much interest in developing transition-metal catalyzed terminal alkyne reactions involving soft and more stable C-M bonds as reaction intermediates, because many such reactions can tolerate water. 

See 1,3-Butadiyne, and Buten-3-yne, both below See METAL ACETYLIDES... 

See Other HALOGENATION INCIDENTS Metal acetylides and carbides... 

See related HALOACETYLENE DERIVATIVES, METAL ACETYLIDES See other silver compounds... 

---