Substituted acetylenes

Hydrazides of vicinal acetylene-substituted derivatives of benzoic and azole carboxylic acids are important intermediate compounds because they can be used for cyclization via both a- and /3-carbon atoms of a multiple bond involving both amine and amide nitrogen atoms (Scheme 131). Besides, the hydrazides of aromatic and heteroaromatic acids are convenient substrates for testing the proposed easy formation of a five-membered ring condensed with a benzene nucleus and the six-membered one condensed with five-membered azoles. 

A more complex reaction is involved in the cooligomerization of acetylenes and tert-butyl isocyanide using nickel acetate as the catalyst (Scheme 20)43 the nature of intermediate complexes leading to the formation of 2-cyano-5-terf-butylaminopyrroles has not been established. Cocyclization of tert-butyl isocyanide with coordinated hexafluoro-2-butyne gives rise to coordinated cyclopentadienone anils for molybdenum systems,44 hence the nature of acetylene substitutents and of the organometallic catalyst play crucial roles in these processes. The pyrrole products from the former reaction can be decomposed by sulfuric acid and the overall sequence provides a simple synthesis of 5-amino-2-cyanopyrroles (Scheme 20). 

Addition of lithium derivatives of acetylenides (Li—C=C-C02R) to chiral nitrones proceeds with high stereoselectivity, giving a-acetylene substituted hydroxylamines (410a,b) (656). This reaction has been successfully applied to the synthesis of y-hydroxyamino-a, 3-ethylene substituted acids (411a,b), formed in the reduction of (410) with Zn in the presence of acid (657, 658), and to chiral 5-substituted-3-pyrroline-2-ones (412a,b) (Scheme 2.184) (658). 

In Scheme 39, new pathways to fused [l,4]thiazines are shown. The oxadiazolone derivative with a mercapto-methyl side chain (308) was reported to react with maleic anhydride to the fused product 309 in high yield <1996M549>. The acetylene substituted triazole 310, when reacted with 2molarequiv of phenylisocyanate, afforded a polysubstituted triazolothiazine derivative 311 via a fairly complicated reaction pathway <1998CJC635>. 

Reaction of the transient zinc intermediates with various electrophiles yielded the acetylenic substitution products and only minor amounts of allenes (Table 9.49). Reactions with aldehydes were non-selective, affording mixtures of stereo- and regioisomeric adducts. However, prior addition of ZnCl2 resulted in the formation of the homopropargylic alcohol adducts with high preference for the anti adduct, as would be expected for an allenylzinc chloride intermediate (Table 9.50). 

Titanium dioxide suspended in an aqueous solution and irradiated with UV light X = 365 nm) converted benzene to carbon dioxide at a significant rate (Matthews, 1986). Irradiation of benzene in an aqueous solution yields mucondialdehyde. Photolysis of benzene vapor at 1849-2000 A yields ethylene, hydrogen, methane, ethane, toluene, and a polymer resembling cuprene. Other photolysis products reported under different conditions include fulvene, acetylene, substituted trienes (Howard, 1990), phenol, 2-nitrophenol, 4-nitrophenol, 2,4-dinitrophenol, 2,6-dinitro-phenol, nitrobenzene, formic acid, and peroxyacetyl nitrate (Calvert and Pitts, 1966). Under atmospheric conditions, the gas-phase reaction with OH radicals and nitrogen oxides resulted in the formation of phenol and nitrobenzene (Atkinson, 1990). Schwarz and Wasik (1976) reported a fluorescence quantum yield of 5.3 x 10" for benzene in water. 

Terminal acetylenes and Ru3(CO)j2 yield complexes of the type [57] (9,190, 336), whereas internal acetylenes form either complexes [56] or acetylene-substituted RU4 complexes (229). Alternatively, two acetylene moieties are incorporated with formation of metallacyclopentadienes (229), a class of compounds more familiar in osmium cluster chemistry (cf. Chapter 3.4.). Instead of two acetylene molecules, one molecule of an arylbutadiene may be the precursor of the metallacycle (382). 

The acetylene substitution reaction proceeds much more rapidly than the related olefin reaction. The acetylene products and starting materials also undergo side reactions such as polymerization concurrently with the substitution. The best yields are obtained when the reactants are diluted with a large excess of amine, or carried out at lower temperatures in methanol with sodium methoxide as the base. Vinylacetylene derivatives can also be prepared by this reaction starting with vinylic halides. For example, ( )-methyl 3-bromo-2-methylpropenoate and r-butylacetylene react in 2 hours at 100° to form the expected vinylacetylene derivative in 59% yield ... 

Some examples of the terminal acetylene substitution reaction are given in Table X. 

In a different pattern, by using silylated acetylenes, substituted pyridazines are obtainable217 from the tetrazine derivative 401 in a diene-type reaction, first introduced by Carboni and Lindsey218. Via this reaction 4-TMS- (402) and 4,5-bis(TMS)-3,6-bis(methoxycarbonyl)pyridazine (403) can be achieved in very high yield, being inert against acid catalyzed desilylation (Scheme 59). 

In this mode, an umpolung of reactivity for the nucleophile occurs, leading to many useful transformations. More complex pathways are not unusual these include addition to multiple bonds, vinylic and acetylenic substitution, rearrangements - some involving ring-expansion or ring-contraction - generation of reactive intermediates, etc. Solvent effects, especially solvent participation, may add new dimensions to reactivity. 

Thus all the data on acetylene substitution are interpreted in terms of a dissociative mechanism with metal-ligand bond cleavage as a limiting step of the reaction. Based on experimental data on replacement of one ligand by another ligand the following sequence of ligand substitution is established. 

The polyimides derived from the dianhydrides had high Tg s of 238 to 466 °C and they were soluble in chlorinated hydrocarbon solvents. Because of their solubility, copolyimides containing the following acetylene substituted diamine monomere were readily prepared by homogeneous high temperature solution polycondensation in m-cresol. 

Scheme 9. Ring expansion of acetylene-substituted squaric add esters and formation of substituted...

Organometallic derivatives of metal carbonyls have been shown to be intermediates in the polymerization and cyclization of acetylenes in the presence of metal carbonyls, and many acetylene derivatives of metal carbonyl compounds have been isolated 43,198). Acetylene-substituted carbonyl clusters have, in general, been prepared by one of two methods. 

Since acetylenic esters of any type, but especially ones with a good leaving group, like sulfonates, were unknown until recently [4], early substrates for nucleophilic acetylenic substitutions [Sn-A] were primarily the haloacetylenes 1 [2, 3, 5]. Unfortunately, product yields in these reactions tend to be moderate at best, usually because of competing reactions including displacement of RC C via direct attack on the halogen itself. 

Formalistically, reactions 63 and 64 are nucleophilic acetylenic substitutions (Sa -A) with the corresponding anions (sulfonate, phosphate or carboxylate) acting as nucleophiles and alkynyliodonium species 97-99 as the electrophilic substrates. However, the actual details of the mechanism are considerably more complex (equation 66). 

The great majority of known2 reactions of acetylenes are with electrophiles either via the acetylide ions RC=C", or by way of electrophilic addition reactions to the triple bond. Nucleophilic acetylenic substitutions (Sat-A) are generally unfavorable2. Alkynyl(phenyl)iodonium species may serve as synthons for the electrophilic alkynyl... 

Condensation of D-glucose with 1,2-diaminobenzene or its 3-substituted-de-rivatives, then with hydrazine, provided the pyrazoloquinoxalines 107/ Triazolopyrimidopurines such as 108 (and a regioisomer) were obtained by cycloaddition of an acetylene-substituted heterocycle with a 1-azido-l-deoxy-alditol derivatives/ ... 

N. Bilow, R. H. Boschan, A. L. Landis, Acetylene-substituted aromatic primary amines and the process of making them, 1975 US Patent 3928450. 

Some plants contain fatty acids only found in a few species. These are termed unusual fatty acids and are often located in seed oils. However, when found, these bizarre structures frequently represent major components of the individual seed being studied. The unusual fatty acids can be conveniently divided into five groups nonconjugated ethylenic, conjugated ethylenic, acetylenic, substituted, and branched-chain. The structures and distribution of some of these acids are shown in Tables II-IV. For a more complete description the reader is referred to Galliard (1974), Hitchcock (1975), Hitchcock and Nichols (1971), Hopkins (1972), and Smith (1970). 

In acetylenes substituted by a substituent of group (A) plus one of group (B), the carboxyl group is added to the C-atom of the triple bond which is substituted by a class (A) substituent. 

N. Bilow, "Acetylene-Substituted Polyimides as Potential High... 

The polycondensation of acetylene-substituted metallocenes has yielded polymers containing backbone aUcyne bridges. The synthesis of l-iodo-2-methoxy-methyl-3-ethynylferreocene and l-iodo-2-(N,N-dimethylamino methyl)-3-ethynyl-ferreocene was reported by Plenio and coworkers. Polymerization of these ferrocene-based complexes gave rise to soluble bimodal 1,3-linked ferrocene-acetylene polymers. Polymers exhibiting optical activity or functionalized sidechains were produced via Sonogashira coupling reactions. 

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