Alkynes and their derivatives

Alkynes are hydrocarbons that contain a carbon-carbon triple bond. A triple bond consists of a cr bond and two tt bonds. The general formula for the alkynes is C li2n-2- The triple bond possesses two elements of unsaturation. Alkynes are commonly named as substituted acetylenes. Compounds with triple bonds at the end of a molecule are called terminal alkynes. Terminal —CH groups are called acetylenic hydrogens. If the triple bond has two alkyl groups on both sides, it is called an internal alkyne. 

Ethyne (acetylene) 1-Butyne (ethylacetylene) 2-Pentyne (ethylmethylacetylene) Terminal alkyne Internal alkyne 

The lUPAC nomenclature of alkynes is similar to that for alkenes, except the -ane ending is replaced with -yne. The chain is numbered from the end closest to the triple bond. When additional functional groups are present, the suffixes are combined. 

The triple bond consists of one cr bond and two tt bonds. Each carbon is bonded to two other atoms, and there are no nonbonding electrons. Carbon 

Terminal alkynes are acidic, and the end hydrogen can be removed as a proton by strong bases (e.g. organolithiums, Grignard reagents and NaNH2) to form metal acetylides and alkynides. They are strong nucleophiles and bases, and are protonated in the presence of water and acids. Therefore, metal acetylides and alkynides must be protected from water and acids. 

---

Name alkynes and their derivatives, and draw correct structures when given their names. 

Biochemistry of triple-bonded functional groups TABLE 2. Distribution of alkynes and their derivatives in higher plants... 

The classification of hydrocarbons as aliphatic or aromatic took place m the 1860s when It was already apparent that there was something special about benzene toluene and their derivatives Their molecular formulas (benzene is CgHg toluene is C7Hj ) indicate that like alkenes and alkynes they are unsaturated and should undergo addition reac tions Under conditions m which bromine for example reacts rapidly with alkenes and alkynes however benzene proved to be inert Benzene does react with Bi2 m the pres ence of iron(III) bromide as a catalyst but even then addition isn t observed Substitu tion occurs instead ... 

Alkenes and alkynes are similar in structure to the alkanes except the alkenes contain a carbon-to-carbon double bond (C=C) and the alkynes contain a carbon-to-carbon triple bond (C=C). The name prefixes are exactly the same as for the alkanes with the same number of carbons, but the endings are -one for compounds with double bonds and their derivatives and -yne for compounds with triple bonds... 

Carboxylic acids and their derivatives like esters, amides, anhydrides, and acyl halides are formally synthesized from olefins, carbon monoxide, and compounds represented by Nu-H such as H2O, ROH, RNH2, RCOOH (Equations (4) and (5)). Alkynes also react under similar conditions to afford the corresponding unsaturated carboxylic acid derivatives. These reactions have been named hydrocarboxylation, hydroalkoxycarbonylation, and hydroaminocarbonylation. 

The following discussion deals not only with this reaction, but related reactions in which a transition metal complex achieves the addition of carbon monoxide to an alkene or alkyne to yield carboxylic acids and their derivatives. These reactions take place either by the insertion of an alkene (or alkyne) into a metal-hydride bond (equation 1) or into a metal-carboxylate bond (equation 2) as the initial key step. Subsequent steps include carbonyl insertion reactions, metal-acyl hydrogenolysis or solvolysis and metal-carbon bond protonolysis. 

A 1,3-dipole is a compound of the type a—Het—b that may undergo 1,3-dipolar cycloadditions with multiply bonded systems and can best be described with a zwitterionic all-octet Lewis structure. An unsaturated system that undergoes 1,3-dipolar cycloadditions with 1,3-dipoles is called dipolarophile. Alkenes, alkynes, and their diverse hetero derivatives may react as dipolarophiles. Since there is a considerable variety of 1,3-dipoles—Table 15.2 shows... 

Diazomethane is an electron-rich 1,3-dipole, and it therefore engages in Sustmann type I 1,3-dipolar cycloadditions. In other words, diazomethane reacts with acceptor-substituted alkenes or alkynes (e. g., acrylic acid esters and their derivatives) much faster than with ethene or acetylene (Figure 15.36). Diazomethane often reacts with unsymmetrical electron-deficient... 

The first alkynyliodonium salt, (phenylethynyl)phenyliodonium chloride, synthesized in low yields from (dichloroiodo)benzene (3) and lithium phenylacetylide (equation 1), was reported in 196526. This chloride salt is unstable and readily decomposes to a 1 1 mixture of chloro(phenyl)acetylene and iodobenzene. It was not until the 1980s, however, that alkynyliodonium salts became generally available. This was made possible by the introduction of sulfonyloxy-/l3-iodanes as synthetic reagents46 and by the recognition that iodosylbenzene (4) can be activated either with boron trifluoride etherate or with triethy-loxonium tetrafluoroborate31. These reagents are now widely employed for the conversion of terminal alkynes and their 1-silyl and 1-stannyl derivatives to alkynyliodonium salts (equations 2 and 3). A more exhaustive survey of iodine(III) reagents that have been... 

As stated in the Introduction, Templeton7 published a comprehensive review entitled Four Electron Alkyne Ligands in Molybdenum(II) and Tungsten(II) Complexes, including halocarbonyl complexes, which dealt with the literature up to 1987. Hence, this section of the review deals with the literature on halocarbonyl alkyne and alkene complexes published from 1987 to mid-1995. The vast majority of papers that have appeared during this period are concerned with the reactions of [MI2(CO)3(NCMe)2] (M = Mo, W) and their derivatives with alkynes, which begin this section of the review. 

Draw and name alkynes, cycloalkynes, and their derivatives. 

Nina A. Nedolya was born in Irkutsk (Russia) and educated in organic chemistry at the Irkutsk State University (Diploma 1972, PhD 1982, DSc 1998). From 1995 to 1999 she was associated with Prof. L. Brandsma at the Utrecht University (The Netherlands). In 1999 she obtained her second PhD from the Utrecht University. She is presently Head of the Research Group of Chemistry of Heterocyclic Compounds at A. E. Favorsky Irkutsk Institute of Chemistry. She is the author of over 210 review articles and research papers. She is also one of the inventors for 112 patents. She is interested in the chemistry of polyfunctional unsaturated heteroatomic systems (vinyl, allenyl, and alkynyl ethers and their derivatives, linear and cyclic heteropolyenes, hetero-cumulenes), including synthesis of important heterocycles, particularly pyrroles, thiophenes, thiazoles, imidazoles, dihydrofurans, dihydropyridines, pyridines, quinolines, dihydroazepines, and azepines, based on metallated allenes or alkynes and/or heterocumulenes. 

Although it may be said that alkylidyne clusters do not contain an unsaturated organic fragment, the chemistry of these compounds is related to that of the alkyne and alkene derivatives, and their synthesis will be discussed briefly. 

The classical version of the Diels-Alder reaction uses a 1,3-diene as the 4it component and an alkene or alkyne containing electron-withdrawing groups (conjugated aldehydes, ketones, acids and their derivatives, nitroalkenes, etc.) as the 2n reactant. With appropriately chosen dienes and/or dienophiles, a wide array of purely carbocyclic or heterocyclic compounds can be easily synthesized. A representative set of simple examples is given in Scheme 2.118. 

B. Functional Groups — Preparation, reactions, and interconversions of alkanes, alkenes, alkynes, dienes, alkyl halides, alcohols, ethers, epoxides, sulfides, thiols, aromatic compounds, aldehydes, ketones, carboxylic acids and their derivatives, amines... 

---