Acetylene: alkylation with

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. ... 

Both MeMn(CO)5 and PhMn(CO)5 react with acetylenes to yield vinyl ketone tetracarbonyl complexes, most likely via a pathway involving CO insertion [Eq. (18)] 14, 36). Reactions of these same alkyls with 1,3-dienes may proceed similarly 16, 95, 96). The chelating ligand o-styryldiphenyl-phosphine (L—L) converts MeMn(CO)j into two products 25) whose structures (XXII and XXIII) were elucidated by X-ray crystallography 24). An unusual migration of COMe onto L—L occurs subsequently to the initial insertion step. 

The reactivity of dichloro carbene towards acetylenic bonds was systematically investigated by Dehmlow19, 20 with respect to substitution of the acetylene, especially those containing additional C-C multiple bonds. It was shown that with aiyl alkyl acetylenes, e.g. 1-phenyl-butyne-l, often the normal cyclopropenone formation occurs only to a minor extent (to yield, e.g. 14), whilst the main reaction consists of an insertion of a second carbene moiety into the original acetylene-alkyl bond (giving, e.g. 15) ... 

All acetylenes with a terminal triple bond are instantaneously converted into the alkali acetylides by alkali amides in liquid ammonia. For many alkylations with primary alkyl halides liquid ammonia is the solvent of choice and the functionalization with oxirane can also be carried out in it with good results. Reactions of ROOM with sulfenyladng agents (R SSR1, R SON, R SSC R ) or elemental sulfur, selenium or tellurium are mostly very successful in ammonia, the same holds for the preparation of ROC1 from RC=CM and iodine. The results of couplings with carbonyl compounds are very variable. 

Exps. 9 and 10 are convincing illustrations of the high lrineiic acidity of the ethynyl proton. In principle, there are four reaction pathways if l-bromo-5-hexyne and a strongly basic reagent are allowed to interact abstraction of the acetylenic proton, Br-metal exchange, displacement of Br by the "nucleophilic" part of the base, and elimination of HBr with formation of HCsC(CH2)2CH=CH2- Only the first process takes place under the conditions of this experiment. The kinetic stability of the intermediate LiOC(CH2)4Br is sufficient to allow for successful functionalizations with a number of reagents. For alkylations with most of the alkyl halides, the polarity of the medium will usually be insufficient. 

Regiospecific alkylation of 1,3-dilithiated acetylenes is a good method for the preparation of branched 1-alkynes dilithiation of 1-butyne, for example, followed by alkylation with RBr, gives HOCCH(R)CH3 in good yields [73]. 

In view of the limited stability of the "carbenoid" LiCsCCP Cl, functionalization reactions have to be carried out a temperatures Lhat are as low as possible. Silylations of meiallated acetylenes are usually rather slow in Et20 at temperatures below -20 C. A small amount of HMPT appears to cause a considerable enhancement of the rates of silylatton with tri-methylchlorosilane. It is not known whether this effect is only due 10 the typical properties of HMPT as a dipolar aprotic solvent (also shown in alkylation with alkyl halides) or whether it is a result of active participation of this solvent in the reaction as depicted in the following equations ... 

The method is not satisfactory for methyl-and ethyl-acetylenes or with secondary and tertiary alkyl halides or with primary alkyl halides above hexyl. 

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. 

Kleinman and co-workers 20 synthesized a lactone precursor to the (2/ ,46, 56 )- -hydroxy-ethylene dipeptide stereoselectively in four steps using the lithium salt of ethyl propiolate as a homoenolate equivalent. As summarized in Scheme 11, addition of ethyl lithiopropiolate to a protected a-amino aldehyde affords hydroxy acetylenic esters as a mixture of dia-stereomers. Reduction of the acetylene group and subsequent lactonization gives a readily separable (4S)-lactone-enriched mixture. Direct alkylation with alkyl halide and lithium hexamethyldisilanazide yields the tram-lactone as the major stereoisomer. 

When acetylene reacts with symmetric ketoximes (75MIP1 79MIP1, 79ZOR602), the corresponding 2-alkyl- and 2,3-dialkylpyrroles and their A-vinyl derivatives are formed (Scheme 3). The yields and physicochemical constants of some typical representatives of the pyrroles synthesized are given in Table VIII. 

Several acetylene derivatives were prepared by alkylation of the terminal acetylene 56 with the requisite alkyl iodides followed by trityl deprotection (Scheme... 

For the syntheses of 2-amino(or 2-imino)-TAs 42,43, and 45 the condensation of acetylenic esters with thiourea and their /V-alkyl derivatives is used most often [62CPB19 64CPB683 67CB3671, 67CJC939 68CPB1351,... 

Acetylene itself and alkyl- and aryl-acetylenes react with diazomethane under more severe conditions, such as 2-5 atmospheres, 20-40°.465-469 By this method 3,3 -dipyrazolyl (38) was synthesized... 

Alkali metal acetylides obtained from acetylenes and sodium in liquid ammonia1 react with tellurium powder to yield sodium ethynetellurolates that are easily alkylated with alkyl halides. 

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