Phenylacetylene alkylation

J-unsaturated ester is formed from a terminal alkyne by the reaction of alkyl formate and oxalate. The linear a, /J-unsaturated ester 5 is obtained from the terminal alkyne using dppb as a ligand by the reaction of alkyl formate under CO pressure. On the other hand, a branehed ester, t-butyl atropate (6), is obtained exclusively by the carbonylation of phenylacetylene in t-BuOH even by using dppb[10]. Reaction of alkynes and oxalate under CO pressure also gives linear a, /J-unsaturated esters 7 and dialkynes. The use of dppb is essen-tial[l 1]. Carbonylation of 1-octyne in the presence of oxalic acid or formic acid using PhiP-dppb (2 I) and Pd on carbon affords the branched q, /J-unsatu-rated acid 8 as the main product. Formic acid is regarded as a source of H and OH in the carboxylic acids[l2]. 

Class (2) reactions are performed in the presence of dilute to concentrated aqueous sodium hydroxide, powdered potassium hydroxide, or, at elevated temperatures, soHd potassium carbonate, depending on the acidity of the substrate. Alkylations are possible in the presence of concentrated NaOH and a PT catalyst for substrates with conventional pX values up to - 23. This includes many C—H acidic compounds such as fiuorene, phenylacetylene, simple ketones, phenylacetonittile. Furthermore, alkylations of N—H, O—H, S—H, and P—H bonds, and ambident anions are weU known. Other basic phase-transfer reactions are hydrolyses, saponifications, isomerizations, H/D exchange, Michael-type additions, aldol, Darzens, and similar... 

Cyclization of substituted phenylacetylene sequences afforded functionalized macrocycles that were amenable to subsequent manipulation. For example, transesterification of 42 with octanol in the presence of 18-crown-6 ether and potassium carbonate gave the corresponding ester in 85% yield (Scheme 13). The ester functionalities could be reduced by DIBALH to give the hydroxymethyl-substituted macrocycle (43) in 61 % yield. The low yield of this particular transformation is attributed to mechanical losses during purification, due to the highly polar nature of the product. Macrocycle 43 could then be treated with alkyl bromides to give a group of benzyl ether derivatized PAMs. 

Complexes 59 and 60 catalyse the hydrosilylation of phenylacetylene (but not other terminal alkyl alkynes) with HSi(Me)jPh. Generally, the Rh analogue is more active than the relative Ir. Both catalysts gave mixtures of all regioisomers, with a preference for the p-Z-isomer, in contrast to what has been reported with other non-NHC cationic complexes of Rh, where the p-f isomers are predominating. Here also the exact nature of the catalytic species is unclear [48],... 

In addition, the most efficient mem-ligand depicted above was successfully applied, in 2006, to the alkynylation of ketones. Thus, Liu et al. showed that this ligand was able to catalyse the enantioselective addition of phenylacetylene to various ketones, using Cu(OTf)2 as the starting base in toluene. The results were excellent and homogeneous not only for substituted aryl alkyl ketones, but also for aliphatic methyl ketones (Scheme 4.6). 

We have also found that ultrasound will promote the liberation of hydrogen from phenylacetylene to give the nucleophile phenylacet-ylide which can be efficiently quenched with an alkyl halide(19) ... 

Phenyl(alkyltelluro)acetylenes (general procedure) n-BuLi (1.35 M in hexane, 22.2 mL, 30 mmol) is added dropwise to phenylacetylene (3.10 g, 30.0 mmol) in THF (15 mL) at 0°C nnder N2. After stirring for 5 min at 0°C, elemental Te (3.90 g, 30.0 mmol) is added and the mixtnre reflnxed nntil the Te disappears ( 30 min). The heat source is removed and the alkyl halide (30 mmol) is added. The mixtnre is stirred for 40 min at room temperatnre, then dilnted with ether (60 mL), washed with brine and the layers separated. The organic phase is dried (MgS04), evaporated and the residne purified by Si02 flash chromatography (elution with hexane). 

A one-pot reaction of phenylacetylene with a dialkyl ditelluride and an alkyl iodide under phase transfer catalysis (method a). The same product can be obtained by using the tellurenyl iodide prepared in situ (method b). ... 

The alkylation proceeds mainly via a trans-mode giving cA-l,2-disubstituted adducts. When an excess of phenylacetylene is used, the yield of the alkylation product is raised (98%, EIZ=9 9l), indicating that the alkylation competes with the self-degradation of n-Bu4Te (to n-Bu2Te, butane and octane). 

Among group 8 transition metal catalysts, iron-based Ziegler-type catalysts such as Fe(acac)3-Et3Al(l 3) (acac = acetylacetonate) have been well known from the early stage of the catalyst investigation, which are readily prepared in situ to polymerize sterically unhindered terminal acetylenes such as -alkyl-, r f-alkyl-, and phenylacetylenes. The formed poly(phenylacetylene) has red color and r-cisoidal structure, and is insoluble and crystalline. 

The alkylation of phenylacetylene with ferf-butyl chloride, benzyl chloride, and diphenylmethyl chloride follows an AdE2 mechanism57-59 with the involvement of the open vinyl cationic intermediate 17 ... 

Friedel-Crafts alkenylation of arenes with various phenylacetylenes to yield 1,1-diarylalkenes was reported. Alkyl-substituted benzenes and naphthalene react with phenylacetylene in the presence of zeolite HSZ-360 to afford the products in good to excellent yields and selectivities 415... 

Well-controlled polymerization of substituted acetylenes was also reported. A tetracoordinate organorhodium complex induces the stereospecific living polymerization of phenylacetylene.600 The polymerization proceeds via a 2-1 -insertion mechanism to provide stereoregular poly(phenylacetylene) with m-transoidal backbone structure. Rh complexes were also used in the same process in supercritical C02601 and in the polymerization of terminal alkyl- and arylacetylenes.602 Single-component transition-metal catalysts based on Ni acetylides603 and Pd acet-ylides604 were used in the polymerization of p-diethynylbenzene. 

Contrasting results are obtained for the peralkylated disilanes RMe2SiSi-Me2R (R = Me, "Bu, Bu), which yield only trace amounts of the 1,4-addition products under the same reaction conditions. Attempts to increase double silylation yields by use of other platinum or palladium catalyst precursors under carbon monoxide pressure or inert atmosphere were also unsuccessful for these peralkylated disilanes. Additionally, the reaction of tetramethyl-l,2-divinyldisilane results in conversion to an intractable product mixture, with no incorporation of the 1,3-diene. Phenyl-substituted disilanes are also effective reagents in the Pt(dba)2-catalyzed double silylation of phenylacetylene, but again, the alkylated disilanes and the vinyl-substituted disilane do not give double silylation products. 

Activation of two Si—Si bonds in bis(disilanyl)alkanes with palladium(O) bis(tert-alkyl isocyanide) induced the formation of the cyclic bis(silyl)palladium(II) bis(terf-alkyl isocyanide) complexes (100) and disilanes described schematically in Scheme 42. These complexes were found to react with phenylacetylene, affording different amounts of five-membered cyclic products and acyclic products which are derived from the insertion of the alkyne into the general intermediate complex 101 (Scheme 42, equation 54). The bis(silanyl)dithiane palladium complex (102) was isolated and characterized in the solid state the two silicon atoms, the two isocyano carbons and the palladium atom are nearly in a plane with a short cross-ring Si—Si distance of 2.613(2) A, suggesting the possibility of covalently bonded two Si—Si atoms in the four-membered ring. Similar reaction with cyclic disilanes afforded oligomers, and cyclic 20-membered compounds have been prepared in the presence of nitriles248,249. 

It has been reported that the cycloaddition of arylimines with nitrosoalkenes proceeds in a 3 + 2-manner, whereas alkylimines cycloadd to nitrosoalkenes in a competitive 3 + 2- and 4 + 2-manner.80 The alkylative 3 + 2-cycloaddition of nitrosoarenes with alkynes, phenylacetylene and methyl propiolate, in the presence of K2CO3-Me2S04 produced /V-meihoxyindoles in high yields. This procedure has been used to prepare the Wasabi phytoalexins, 3-carboxy-A-alkoxyindoles.81... 

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