Alkynyls reactivity

Alkynyl anions are more stable = 22) than the more saturated alkyl or alkenyl anions (p/Tj = 40-45). They may be obtained directly from terminal acetylenes by treatment with strong base, e.g. sodium amide (pA, of NH 35). Frequently magnesium acetylides are made in proton-metal exchange reactions with more reactive Grignard reagents. Copper and mercury acetylides are formed directly from the corresponding metal acetates and acetylenes under neutral conditions (G.E. Coates, 1977 R.P. Houghton, 1979). 

Other pseudo-halides are used for carbonylation. Phenyl tluorosulfonate (484) can be carbonylated to give benzoate[337]. Aryl(aryl)iodonium salts[338], aryl(alkenyl)iodonium salts (485)[339], and arylialkynyl)iodonium salts (486)[340] are reactive compounds and undergo carbonylation under mild conditions (room temperature, 1 atm) to give aryl, alkenyl, and alkynyl esters. lodoxybenzene (487) is carbonylated under mild conditions in... 

The allenyl moiety (2,3-aikadienyl system) in the carbonylation products is a reactive system and further reactions such as intramolecular Diels-Alder and ene reactions are possible by introducing another double bond at suitable positions of the starting 2-alkynyl carbonates. For example, the propargylic carbonate 33 which has l,8(or 1.9)-diene-3-yne system undergoes tandem carbonylation and intramolecular Diels-Alder reaction to afford the polycyclic compound 34 under mild conditions (60 C, 1 atm). The use of dppp as ligand is important. One of the double bonds of the allenyl ester behaves as part of the dieneflSj. 

The alkynylation of estrone methyl ether with the lithium, sodium and potassium derivatives of propargyl alcohol, 3-butyn-l-ol, and propargyl aldehyde diethyl acetal in pyridine and dioxane has been studied by Miller. Every combination of alkali metal and alkyne tried, but one, gives the 17a-alkylated products (65a), (65c) and (65d). The exception is alkynylation with the potassium derivative of propargyl aldehyde diethyl acetal in pyridine at room temperature, which produces a mixture of epimeric 17-(3, 3 -diethoxy-T-propynyl) derivatives. The rate of alkynylation of estrone methyl ether depends on the structure of the alkyne and proceeds in the order propar-gylaldehyde diethyl acetal > 3-butyn-l-ol > propargyl alcohol. The reactivity of the alkali metal salts is in the order potassium > sodium > lithium. 

McDowell and Stirling194 studied electronic effects upon the reactivity of aryl vinyl sulfones towards amines. Rate constants for t-butylamine addition in ethanol at 25 °C were well correlated by the Hammett equation, with p = 1.59. Comparison of this with p values for H-D exchange mentioned above191 suggested considerable carbanionic character in the transition state, perhaps in a concerted mechanism. Rates of addition of amines to alkenyl, allenyl and alkynyl p-tolyl sulfones have also been measured195. 

Fischer-type carbene complexes, generally characterized by the formula (CO)5M=C(X)R (M=Cr, Mo, W X=7r-donor substitutent, R=alkyl, aryl or unsaturated alkenyl and alkynyl), have been known now for about 40 years. They have been widely used in synthetic reactions [37,51-58] and show a very good reactivity especially in cycloaddition reactions [59-64]. As described above, Fischer-type carbene complexes are characterized by a formal metal-carbon double bond to a low-valent transition metal which is usually stabilized by 7r-acceptor substituents such as CO, PPh3 or Cp. The electronic structure of the metal-carbene bond is of great interest because it determines the reactivity of the complex [65-68]. Several theoretical studies have addressed this problem by means of semiempirical [69-73], Hartree-Fock (HF) [74-79] and post-HF [80-83] calculations and lately also by density functional theory (DFT) calculations [67, 84-94]. Often these studies also compared Fischer-type and... 

Complexes with unsaturated ligands (a-vinyl. a-allyl, and alkynyl) have been reported, each prepared from Fe(TPP)CI with the appropriate Grignard (vinyl, 2- methylvinyl.2,2-dimethylvinyl,allyl,or2-methylallyl)orlithiumreagent(LiC= C-n-Pr or LiC CPh) and observed by NMR spectroscopy (Scheme 4). The vinyl and alkynyl complexes are stable in solution at 25 C, whereas the allyl species decompose quickly if allowed to warm to room temperature. All were too reactive to be purihed by chromatography. The vinyl and allyl complexes show characteristic low spin behavior, although the temperature dependence of the vinyl... 

The low spin aryliron complexes Fe(Por)Ar behave differently than their alkyl counterparts toward oxygen. In chloroform the products of the reaction of Fe(Por)Ar with O2 are the iron(IV) alkyl Fe(Por)Ar] and Fe(Por)Cl, while in toluene the aryloxide complexes Fe(Por)OAr are formed with no direct evidence for the formation of arylperoxo intermediates."" The high spin iron(lll) alkynyl complexes which have more ionic character in the Fe—C bond do not react with oxygen, and the order of reactivity of organoiron(lll) complexes toward O2 is given by Fe(Por)(alkyl) > Fe(Por)(aryl) > Fe(Por)(C=CR). ... 

Bardaji, M., Lagrma, A. and Jones, P.G. (2001) Reactivity of anAcetylenephosphine Gold(III) Precursor Addition to the Triple Bond or Formation of Alkynyl Derivatives. Organometallics, 20(18), 3906-3912. 

Whereas Ullmann chemistry is limited to the coupling of aryl halides, a variety of species including aryl-, alkynyl-, alkenyl-, and alkylcopper species can be produced which are highly reactive toward other substrates. 

React at room temperature for up to 3 days (or at 4°C, if the protein is not stable at ambient temperature). The optimal time of reaction is dependent on the protein being coupled and the number of alkyne reactive groups available. An alkynyl-protein added to the nanoparticles at a high molar ratio probably would reach maximal coupling yield in a matter of hours. 

Furoxan and furazans alcohols are relatively uncommon compounds, but they can serve as useful precursors to various new derivatives of 1,2,4-oxadiazole. 3-Hydroxy-4-nitrofurazan 208 reacts with iodosylbenzene to produce a highly reactive intermediate phenyliodonium nitrofurazanylate 209 which can be converted to a series of alkynyl(phenyl)-iodonium nitrofurazanylates and related products (Scheme 48) <2001TL5759>. 

In summary, the detailed electronic character of dihapto metal-acetylene complexes depends strongly on the Lewis-acceptor capacity of the metal. Formal two-versus four-electron rp ligation to a transition metal can lead to breaking of one or both 7T bonds, dramatically altering the structure and reactivity of the alkynyl... 

The second reason for the lower yields is the high reactivity of the intermediate. Two molecules of the alkynyl bromide react in a stepwise manner with the zirconacyclopentadiene. When one alkynyl halide molecule couples with the zirconacyclopentadiene, the intermediate bears a metalladienyne moiety (as in 50), as shown in Eq. 2.36... 

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