Alkynes => alkyl halides

Naming Cycloalkanes, Alkenes, Alkynes, Alkyl Halides, Alcohols, Ethers, and Amines... 

Pd(ll) catalysts can be employed as well. Compared to the standard Pd(ll) catalysts, the palladacycle catalyst 7 shows a broader compatibility with functional groups. Terminal alkynes, alkyl halides, and a-halogen ketones are tolerated <1997CB1449>. It is worth mentioning that other catalysts of Pd(ll) preferentially give dimerization products. 

Triphenylsilyl ethers are typically prepared by the reaction of the alcohol with triphenylsilyl chloride (mp 92-94 °C) and imidazole in DMF at room temperature. The dehydrogenative silylation of alcohols can be accomplished with as little as 2 mol% of the commercial Lewis acid tris(pentaf1uorophenyl)borane and a silane such as triphenylsilane or triethylsilane [Scheme 4.98]. Primary, secondary, tertiary and phenolic hydroxyls participate whereas alkenes, alkynes, alkyl halides, nitro compounds, methyl and benzyl ethers, esters and lactones are inert under the conditions. The stability of ether functions depends on the substrate. Thus, tetrahydrofurans appear to be inert whereas epoxides undergo ring cleavage. 1,2- and 1,3-Diols can also be converted to their silylene counterparts as illustrated by the conversion 983 98.4. Hindered silanes such as tri-... 

Carbon-Carbon Bond Formation. Various types of Bronsted and Lewis acids and superacids may be applied to perform the reaction of alkanes or arenes with different alkylating agents (alkenes, alkynes, alkyl halides, alcohols, ethers, esters). Acid-catalyzed alkylations, particularly alkane-alkene reactions, are of great practical importance in upgrading motor fuels. Acid-catalyzed alkylation produces alkylaromatics for manufacture of plastics (styrenes), detergents, and chemicals. 

Alkanes can be prepared via FGI starting with a variety of functional groups, including alkenes, alkynes, alkyl halides, alcohols, ketones, and aldehydes. In each case, the functional group is being replaced by simple C-H bonds, so these transformations will aU be described as reduction reactions. 

A map of reactions for interconversion between alkanes, alkenes, alkynes, alkyl halides, alcohols, and ketones/aldehydes. 

In some cases where a reaction involving a radical species occurred within cobalt porphyrin complexes, it has been possible to trap transient cobalt porphyrin hydride species. This was indeed observed during the synthesis of organocobalt porphyrin that resulted from the reaction of cobalt(n) porphyrin and dialkylcyanomethylradicals with alkenes, alkynes, alkyl halides, and epoxide. A transient hydride porphyrin complex was also involved in the cobalt porphyrin-catalyzed chain transfer in the free-radical polymerization of methacrylate. The catalytic chain transfer in free-radical polymerizations using cobalt porphyrin systems has been extensively investigated and will not be treated in this section. Gridnev and Ittel have published a comprehensive overview of the catalytic chain transfer in free-radical polymerizations. ... 

Sheppard N and De La Cruz C 1998 Vibrational spectra of hydrocarbons adsorbed on metals. Part II. Adsorbed acyclic alkynes and alkanes, cyclic hydrocarbons including aromatics and surface hydrocarbon groups derived from the decomposition of alkyl halides, etc Adv. Catal. 42 181-313... 

The higher homologues of propyne, e.g. 1-decyne, can be obtained in a similar way. Starting from 1-butyne and its homologues, alkylation with alkyl halides leads to 1-alkynes with a branched substituent. 

In Grignard reactions, Mg(0) metal reacts with organic halides of. sp carbons (alkyl halides) more easily than halides of sp carbons (aryl and alkenyl halides). On the other hand. Pd(0) complexes react more easily with halides of carbons. In other words, alkenyl and aryl halides undergo facile oxidative additions to Pd(0) to form complexes 1 which have a Pd—C tr-bond as an initial step. Then mainly two transformations of these intermediate complexes are possible insertion and transmetallation. Unsaturated compounds such as alkenes. conjugated dienes, alkynes, and CO insert into the Pd—C bond. The final step of the reactions is reductive elimination or elimination of /J-hydro-gen. At the same time, the Pd(0) catalytic species is regenerated to start a new catalytic cycle. The transmetallation takes place with organometallic compounds of Li, Mg, Zn, B, Al, Sn, Si, Hg, etc., and the reaction terminates by reductive elimination. 

Anions of acetylene and terminal alkynes are nucleophilic and react with methyl and primary alkyl halides to form carbon-carbon bonds by nucleophilic substitution Some useful applications of this reaction will be discussed m the following section... 

Just as It IS possible to prepare alkenes by dehydrohalogenation of alkyl halides so may alkynes be prepared by a double dehydrohalogenation of dihaloalkanes The dihalide may be a geminal dihalide, one m which both halogens are on the same carbon or it may be a vicinal dihalide, one m which the halogens are on adjacent carbons... 

The properties of organometallic compounds are much different from those of the other classes we have studied to this point Most important many organometallic com pounds are powerful sources of nucleophilic carbon something that makes them espe cially valuable to the synthetic organic chemist For example the preparation of alkynes by the reaction of sodium acetylide with alkyl halides (Section 9 6) depends on the presence of a negatively charged nucleophilic carbon m acetylide ion... 

These compounds are sources of the nucleophilic anion RC=C and their reaction with primary alkyl halides provides an effective synthesis of alkynes (Section 9 6) The nucleophilicity of acetylide anions is also evident m their reactions with aldehydes and ketones which are entirely analogous to those of Grignard and organolithium reagents... 

Both CH3CH2CH2C=CH and CH3CH2C=CCH3 can be prepared by alkylation of acety lene The alkyne (CH3)2CHC=CH cannot be prepared by alkylation of acetylene because the required alkyl halide (CH3)2CHBr is secondary and will react with the strongly basic acetylide ion by elimination... 

Hydrogenation of alkynes to alkenes using the Lindlai catalyst is attractive because it sidesteps the regioselectivity and stereoselectivity issues that accompany the dehydration of alcohols and dehydrohalogenation of alkyl halides. In tenns of regioselectivity, the position of the double bond is never in doubt—it appears in the carbon chain at exactly the sane place where the triple bond was. In tenns of stereoselectivity, only the cis alkene forms. Recall that dehydration and dehydrohalogenation normally give a cis-trans mixture in which the cis isomer is the minor product. 

Reaction with Alkyl Halides The gas inlet tube is replaced by an addition funnel, and 10 ml of HMPT is added rapidly with stirring. The mixture is cooled to 10-15°, and a solution of the alkyl halide (0.1 mole) in 20 ml of THF is added dropwise over a period of 30-40 minutes. The mixture is then heated to 40° for 2-3 hours. The thick white suspension of the sodium halide is cooled and dilute cold hydrochloric acid is carefully added until the mixture is clear. The organic layer is separated, and the aqueous layer is extracted three times with 20-ml portions of ether, the ethereal extracts then being combined with the organic material. The ethereal solution is washed twice with saturated sodium chloride solution and dried. The ether and THF are removed under reduced pressure (rotary evaporator), and the alkyne is distilled. 

Alkynes can be prepared by the elimination of HX from alkyl halides in much the same manner as alkenes (Section 7.1). Treatment of a 1,2-dihaloaJkane (a vicinal dihalide) with excess strong base such as KOH or NaNH2 results in a twofold elimination of HX and formation of an alkyne. As with the elimination of HX to form an alkene, we ll defer a discussion of the mechanism until Chapter 11. 

The negative charge and unshared electron pair on carbon make an acetylide anion strongly nucleophilic. As a result, an acetylide anion can react with an alkyl halide such as bromomethane to substitute for the halogen and yield a new alkyne product. 

Alkyne alkylation is not limited to acetylene itself. Any terminal alkyne can be converted into its corresponding anion and then alkylated by treatment with an alkyl halide, yielding an internal alkyne. For example, conversion of 1-hexyne into its anion, followed by reaction with 1-bromobutane, yields 5-decyne. 

Problem 8.10 Show the terminal alkyne and alkyl halide from which the following products can be obtained. If two routes look feasible, list both. 

What is an immediate precursor of a terminal alkyne " Perhaps sodium acetylide and an alkyl halide. 

An alkyne is a hydrocarbon that contains a carbon-carbon triple bond. Alkyne carbon atoms are sp-hybridized, and the triple bond consists of one sp-sp a bond and two p-p tt bonds. There are relatively few general methods of alkyne synthesis. Two good ones are the alkylation of an acetylide anion with a primary-alkyl halide and the twofold elimination of HX from a vicinal dihalide. 

DNA sequencing and. 1113 Electrospray ionization (ESI) mass spectrometry, 417-418 Electrostatic potential map, 37 acetaldehyde, 688 acetamide, 791,922 acetate ion. 43. 53, 56, 757 acetic acid. 53. 55 acetic acid dimer, 755 acetic anhydride, 791 acetone, 55, 56. 78 acetone anion, 56 acetyl azide, 830 acetyl chloride, 791 acetylene. 262 acetylide anion, 271 acid anhydride, 791 acid chloride, 791 acyl cation, 558 adenine, 1104 alanine, 1017 alanine zwitterion, 1017 alcohol. 75 alkene, 74, 147 alkyl halide, 75 alkyne. 74... 

A microwave-assisted three-component reaction has been used to prepare a series of 1,4-disubstituted-1,2,3-triazoles with complete control of regiose-lectivity by click chemistry , a fast and efficient approach to novel functionalized compounds using near perfect reactions [76]. In this user-friendly procedure for the copper(l) catalyzed 1,3-dipolar cycloaddition of azides and alkynes, irradiation of an alkyl halide, sodium azide, an alkyne and the Cu(l) catalyst, produced by the comproportionation of Cu(0) and Cu(ll), at 125 °C for 10-15 min, or at 75 °C for certain substrates, generated the organic azide in situ and gave the 1,4-disubstituted regioisomer 43 in 81-93% yield, with no contamination by the 1,5-regioisomer (Scheme 18). 

The tin hydrides find important applications as reducing agents. Many of their reactions (particularly the reduction of alkyl halides and the hydrostannation of simple alkenes and alkynes) arc known to proceed through RaSn- intermediates, and this aspect of their chemistry is referred to in Section II,G. 

Haloalkynes (R—C=C—X) react with ArSnBu3 and Cul to give R—C= C—Ar. Acetylene reacts with two equivalents of iodobenzene, in the presence of a palladium catalyst and Cul, to give 1,2-diphenylethyne. 1-Trialkylsilyl alkynes react with 1-haloalkynes, in the presence of a CuCl catalyst, to give diynes and with aryl triflates to give 1-aryl alkynes. Alkynes couple with alkyl halides in the presence of Sml2/Sm. Alkynes react with hypervalent iodine compounds " and with reactive alkanes such as adamantane in the presence of AIBN. ... 

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