Formation of Acetylenic Alcohols

The reaction is carried out in dioxane, hexametapol, and sulfolane (100°C-140°C, the initial acetylene pressure 12 atm). Catalyst and solvent have the most essential impact on the yield of carbynol. The efficiency of the studied catalysts drops in the following order KOH RbOH [(C4H9)4N+]-OH NaOH. LiOH and Rb(Tl do not catalyze the reaction. Aqueous DMSO is the easiest medium to prepare acetylenic alcohol dioxane takes the second place in terms of efficiency. The addition of DMSO to dioxane does not almost improve the carbynol yield. In hexametapol and sulfolane, 1-ethynyl-l-cyclohexanol is formed in trace amounts only. 

The formation of ammonium is always observed in the course of the reaction. Though it is a common knowledge [331] that some ketoximes, upon heating with metal hydroxides, partially regenerate ketones and release ammonium, nevertheless, cyclohexanone likely is not an intermediate product of this reaction. This follows from a special experiment with cyclohexanone, acetylene and ammonium, the reaction of which results in a complex mixture of products containing no 1-ethynyl-l-cyclohexanol [175]. 

Almost entire inertness of cyclohexanone oxime in the experiments with NaOH and tetrabutylammonium hydroxide testify against the intermediate formation of cyclohexanone. 

In optimum (or close to them) conditions of pyrroles and N-vinylpyrroles synthesis from ketoximes and acetylene in the system KOH/DMSO, acetylenic alcohols are not almost formed. 

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Using this hydrogenation as the final step simplifies the problem to a synthesis of this acetylenic alcohol. We know how to form carbon-carbon bonds next to triple bonds, and we have seen the formation of acetylenic alcohols (Section 9-7B). 

Normant and coworkers demonstrated that the intermolecular carbomagnesiation across acetylene (HC=CH) could be catalyzed by a copper salt . The treatment of w-heptylmag-nesium bromide with acetylene in the presence of a catalytic amount of CuBr (5 mol%) in EtgO at —20 °C followed by the reaction with C2H5CHO and quenching with H2O results in the formation of allylic alcohol 12 in 31% yield (Scheme 9) . The carbomagnesiation takes place in a yw-addition manner. 

The electrochemical allylation of carbonyl compounds by electroreductivc regeneration of a diallyltin reagent from allyl bromide and a Sn species leads to formation of homoallylic alcohols in yields of 70-90 % even in methanol or methanol/water (Table 7, No. 12) Bisaryl formation is possible also from aryl iodides or bromides in the presence of electro-generated Pd phosphane complexes (Table 7, No. 13) In the presence of styrenes, 1,3-butadienes, or phenyl acetylene the products of ArH addition are formed in this way (Table 7, No. 14) . The electroreductivc cleavage of allylic acetates is also possible by catalysis of an Pd°-complex (Table K No. 15)... 

The ring-opening addition of 2-dialkyIamino tetrahydropyran [59] or 1,3-oxazoIidine [60], leading to formation of acetylenic alkylamino alcohols has been reported. In the same way, substituted aldose, which has the structure of cyclohemiacetals, yields dihydroxy alkynes (see Table 4, entries 7-9) [61]. 

Pyrolysis of poly(1,4-butylene terephthalate) is in some respects similar to that of poly(ethylene terephthalate) and generates compounds such as benzoic acid, terephthalic acid dibutylene ester, probably terephthalic acid, etc. Also the formation of CO, CO2, benzene, biphenyl, etc. is similar. On the other hand, the percentage distribution of different compounds is rather different for poly(1,4-butylene terephthalate). A relatively high level of butadiene is generated from this polymer, white in the case of PET, formation of acetylene would not be thermodynamically possible and acetaldehyde is formed. Also, the esters of terephthalic acid with C4 alcohols are at considerably higher levels in the pyrolysate of PBT, which seems to indicate that they are more stable than the corresponding esters with C2 alcohols in PET pyrolysate. 

Oxygenation of carbanions. The a1 transforming carbanions into alcohols [Pg.70]

Oxygenation of carbanions. The alkoxide form (i.e., (-BuOOLi) is capable of transforming carbanions into alcohols (after subsequent protonation). Of particular interest is the formation of acetylene oxides. 

DAIB =((-)-3-exo-(Dimethylamino)isobomeol) was introduced as a chiral auxiliary (AX) for the enantioselective addition of dialkylzincs to aldehydes [112]. It has been applied for both intermolecular [113a] and intramolecular [113b] formation of ( -aIlyl alcohols from acetylenes and aldehydes via (l-alkenyl)(alkyl)zinc intermediates. 

It has been noted that the synthesis of pyrroles from ketoximes and acetylene in some case leads to tertiary a-acetylenic alcohols [4,5,7], It indicates a possibility of oxime involvement into the Favorsky alkynol synthesis. The conditions of acetylenic alcohols formation from ketoximes and acetylene have been investigated on the example of the reaction between cyclohexanone oxime and acetylene (Scheme 1.160) [175]. 

Acetaldehyde [75-07-0] (ethanal), CH CHO, was first prepared by Scheele ia 1774, by the action of manganese dioxide [1313-13-9] and sulfuric acid [7664-93-9] on ethanol [64-17-5]. The stmcture of acetaldehyde was estabhshed in 1835 by Liebig from a pure sample prepared by oxidising ethyl alcohol with chromic acid. Liebig named the compound "aldehyde" from the Latin words translated as al(cohol) dehyd(rogenated). The formation of acetaldehyde by the addition of water [7732-18-5] to acetylene [74-86-2] was observed by Kutscherow] in 1881. 

Ma.nufa.cture. The principal manufacturers of A/-vinyl-2-pyrrohdinone are ISP and BASF. Both consume most of their production captively as a monomer for the manufacture of PVP and copolymers. The vinylation of 2-pyrrohdinone is carried out under alkaline catalysis analogous to the vinylation of alcohols. 2-Pyrrohdinone is treated with ca 5% potassium hydroxide, then water and some pyrroHdinone are distilled at reduced pressure. A ca 1 1 mixture (by vol) of acetylene and nitrogen is heated at 150—160°C and ca 2 MPa (22 atm). Fresh 2-pyrrohdinone and catalyst are added continuously while product is withdrawn. Conversion is limited to ca 60% to avoid excessive formation of by-products. The A/-vinyl-2-pyrrohdinone is distilled at 70-85°C at 670 Pa (5 mm Hg) and the yield is 70-80% (8). 

The direct combination of selenium and acetylene provides the most convenient source of selenophene (76JHC1319). Lesser amounts of many other compounds are formed concurrently and include 2- and 3-alkylselenophenes, benzo[6]selenophene and isomeric selenoloselenophenes (76CS(10)159). The commercial availability of thiophene makes comparable reactions of little interest for the obtention of the parent heterocycle in the laboratory. However, the reaction of substituted acetylenes with morpholinyl disulfide is of some synthetic value. The process, which appears to entail the initial formation of thionitroxyl radicals, converts phenylacetylene into a 3 1 mixture of 2,4- and 2,5-diphenylthiophene, methyl propiolate into dimethyl thiophene-2,5-dicarboxylate, and ethyl phenylpropiolate into diethyl 3,4-diphenylthiophene-2,5-dicarboxylate (Scheme 83a) (77TL3413). Dimethyl thiophene-2,4-dicarboxylate is obtained from methyl propiolate by treatment with dimethyl sulfoxide and thionyl chloride (Scheme 83b) (66CB1558). The rhodium carbonyl catalyzed carbonylation of alkynes in alcohols provides 5-alkoxy-2(5//)-furanones (Scheme 83c) (81CL993). The inclusion of ethylene provides 5-ethyl-2(5//)-furanones instead (82NKK242). The nickel acetate catalyzed addition of r-butyl isocyanide to alkynes provides access to 2-aminopyrroles (Scheme 83d) (70S593). 

The reaction can be performed under a variety of conditions. Origin-aiiyi2o,i26,234 acetylene and potassium in liquid ammonia were used. Subsequently, this was simplified by the use of potassium r-amylate in r-amyl alcohol and later this system was found to react selectively at C-17 in the presence of an A-ring a,j5-unsaturated ketone. A closer investigation of these reaction conditions revealed the formation of a small amount (2-3 %) of the disubstituted acetylene this can be avoided by reacting the 17-keto steroid with acetylenedimagnesium bromide in ether-tetrahydrofuran (see chapter 10.)... 

Methylsulfinyl carbanion (dimsyl ion) is prepared from 0.10 mole of sodium hydride in 50 ml of dimethyl sulfoxide under a nitrogen atmosphere as described in Chapter 10, Section III. The solution is diluted by the addition of 50 ml of dry THF and a small amount (1-10 mg) of triphenylmethane is added to act as an indicator. (The red color produced by triphenylmethyl carbanion is discharged when the dimsylsodium is consumed.) Acetylene (purified as described in Chapter 14, Section I) is introduced into the system with stirring through a gas inlet tube until the formation of sodium acetylide is complete, as indicated by disappearance of the red color. The gas inlet tube is replaced by a dropping funnel and a solution of 0.10 mole of the substrate in 20 ml of dry THF is added with stirring at room temperature over a period of about 1 hour. In the case of ethynylation of carbonyl compounds (given below), the solution is then cautiously treated with 6 g (0.11 mole) of ammonium chloride. The reaction mixture is then diluted with 500 ml of water, and the aqueous solution is extracted three times with 150-ml portions of ether. The ether solution is dried (sodium sulfate), the ether is removed (rotary evaporator), and the residue is fractionally distilled under reduced pressure to yield the ethynyl alcohol. 

Silylated acetylenic alcohols such as 1500 cyclize on treatment with HMDS-Li to give, via 1501 and 1502, 2-phenylpyrrole 1503 [46] (Scheme 9.27 compare also the formation of 2-pyridyl-2-pyrrole 543 in Chapter 5). 

An accident of the same nature happened when it was dried with diphosphorus pentoxide. In this case, it is unlikely that the reason for it is the formation of an acetylene salt. The author believes that, since water plays a desensitising role on this compound, it leads to a very unstable pure alcohol when it is removed by strong dehydrating agents. The temperature rise due to the dessicating agent hydration is sufficient to decompose the pure alcohol violently.This interpretation could also be applied to the previous case. 

Metal-catalyzed C-H bond formation through isomerization, especially asymmetric variant of that, is highly useful in organic synthesis. The most successful example is no doubt the enantioselective isomerization of allylamines catalyzed by Rh(i)/TolBINAP complex, which was applied to the industrial synthesis of (—)-menthol. A highly enantioselective isomerization of allylic alcohols was also developed using Rh(l)/phosphaferrocene complex. Despite these successful examples, an enantioselective isomerization of unfunctionalized alkenes and metal-catalyzed isomerization of acetylenic triple bonds has not been extensively studied. Future developments of new catalysts and ligands for these reactions will enhance the synthetic utility of the metal-catalyzed isomerization reaction. 

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). 

Acid-catalyzed rearrangement of tertiary a-acetylenic (terminal) alcohols, leading to the formation of a,(3-unsaturated ketones rather than the corresponding a,(3-unsaturated aldehydes. Cf. Meyer-Schuster rearrangement. 

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