2- Butyne isomerization

Acetylene is also protected as propargyl alcohol (300)[2H], which is depro-tected by hydrolysis with a base, or oxidation with MnOi and alkaline hydrolysis. Sometimes, propargyl alcohols are isomerized to enals. Propargyl alcohol (300) reacts with 3-chloropyridazine (301) and EtiNH to give 3-diethylami-noindolizine (303) in one step via the enal 302[2I2]. Similarly, propargyl alcohol reacts with 2-halopyridines and secondary amines. 2-Methyl-3-butyn-2-ol (304) is another masked acetylene, and is unmasked by treatment with KOH or NaOH in butanol[205,206,213-2l5] or in situ with a phase-transfer cata-lyst[2l6]. 

Isothiocyanates (R,NCS) react with l,4-diamino-2-butynes to give 2-amino-5-p-aminoethylidene-A-2-thiazolines, which can be isomerized into 2-amino-5-p-aminoethylthiazoles with Rj, R2, Rs = alkyl (Scheme 130) (789). 

Give the structures of three isomeric dibromides that could be used as starting materials for the preparation of 3 3 dimethyl 1 butyne J... 

A one-pot three-step conversion of aryl fluorides to phenols based on a consecutive nucleophilic aromatic substitution/isomerization/hydrolysis sequence has been reported by Levin and Du (Scheme 6.126) [256], The authors discovered that 2-butyn-l-ol can function as a hydroxyl synthon through consecutive SNAr displacement, in situ isomerization to the allenyl ether, and subsequent hydrolysis, to afford phenols rapidly and in good yields. In most cases, excesses of 2-butyn-l-ol (1-2 equivalents) and potassium tert-butoxidc (2-4 equivalents) were required in order to achieve optimum yields. 

In 1982, the ruthenium-catalyzed isomerization of 2-butyne-l,4-diol to butyrolactone was reported. This reaction was proposed to proceed through initial isomerization of 2-butyne-l,4-diol to a,/3-unsaturated aldehyde followed by cyclization and double bond isomerization (Scheme 52).91... 

Complex condensation products are obtained by reaction of the alkyne complex with excess of 3,3-dimethyl-l-butyne, which yields two isomeric products of formulas Ru3(CO)6[HC2C(Me)3-COCH2CMe3][HC2CMe3]2 (125). The X-ray structure of one of those adducts (Fig. 19) shows that both dimerization of two alkyne molecules and the insertion of carbon monoxide into the alkyne metal bonds have occurred. The Ru-Ru distances of 2.820,2.828, and 2.686 A in the ring are of interest. The value of 2.686 A is one of the shortest found in a... 

In another study the kinetics and mechanism of an unprecedented T/2-vinyl isomerization of a highly fluorinated tungsten(II) metalla-cyclopropene complex was studied (92). Photolysis of a tungsten(II) tetrafluoroaryl metallacycle 1 and perfluoro-2-butyne results in the formation of the kinetic rf -vinyl complex 2 in which the fluoride is trans to the inserted acetylene and cis to both carbonyl ligands. Upon heating 2 is converted to the thermodynamic rf -vinyl complex 3 in which the fluoride ligand is now cis to the inserted alkyne and trans to one CO and cis to the second CO ligand as shown in Scheme 1. 

The next homologues are 1- and 2-butyne, where similar isomerizations have been observed [20] a recent report describes the reaction on a basic, alkali metal-exchanged zeolite [21]. As an unexpected product, an allene was obtained in reactions with hydrogen and a samarium catalyst [16, 22]. 

Of further significance is the fact that no 1,3-pentadiene is formed This behavior is similar to that of the butynes, where also no 1,3-butadiene was observed. Furthermore, this is in complete accordance with the proposed mechanism of the potassium 3-aminopropylamide-mediated isomerization of internal alkynes to terminal alkynes by repetitive alkyne-allene-alkyne isomerizations [24]. 

Dimethylamino-l-butyne (282) undergoes a base-catalysed isomerization to 2-dimethylamino-1,3-butadiene (283)312. 

Some 3-amino-1-butynes have been reported to rearrange in the vapor phase to the isomeric 2-amino-1,3-butadienes or when heated from 10° to 30°C above their boiling point [81] (Eq. 26). Similarly, l,4-bis(dialkylamino)-... 

Zirconocene diiodide can promote the addition of diallylzinc to a,/1-disubstituted unactivated alkynes. Thus, in the case of 5-decyne, a 94/6 mixture of the two isomeric alkenyl iodides (derived respectively from syn and anti additions to the triple bond) was obtained after iodinolysis (equation 74)108. However, the stereoselectivity was lower for 2-butyne (80/20) and the case of unsymmetrical alkynes was not mentioned. 

In each of the alkyne metatheses outlined here, the byproduct is the volatile 2-butyne. The alkyne metathesis can only be carried out on internal alkynes, since the metathesis catalysts cyclotrimerize terminal alkynes such as 11 to benzene derivatives. In this context, it may prove useful that readily-available terminal alkynes such as 14 are easily isomerized specifically to methyl alkynes such as 15... 

The first rearrangement involving an acetylenic compound was reported by Favorskii133 as early as 1887. He found that when 1-butyne and higher-molecular-weight straight-chain 1-alkynes are heated with an alcoholic solution of potassium hydroxide, they are isomerized to 2-alkynes ... 

A unique mechanism was suggested to interpret the difference observed in the isomerization and hydrogenation of 1-butene and ds-2-butene over a stepped Pt(775) surface.360 It was observed that the hydrogenation rates were insensitive to surface structure for both 1-butene and ds-2-butene. The isomerization rates of cis-2-butene to give only trans-2-butene on the stepped Pt(775) surface, however, was double that of 1-butene to yield both cis- and trans-2-butenes. The Horiuti-Polanyi associative mechanism, that is, the involvement of the 2-butyl intermediate (see Section 4.3.2), cannot explain this difference. However, a facile dehydrogenation of ds-2-butene to 2-butyne followed by a rehydrogenation is consistent with the experimental observations ... 

Notice that cis-trans isomerism is not possible at a carbon-carbon triple bond, as for 2-butyne, because the bonding arrangement at the triply bonded carbons is linear ... 

The basic catalyst in the isomerization of 1,2-butadienes to butynes acts by removing an alkenic proton from the hydrocarbon. Two different anions can be formed, each of which is stabilized by electron delocalization involving the adjacent multiple bond. Either anion can react with the solvent by proton transfer to form the starting material or an alkyne. At equilibrium the most... 

When we reacted hexafluoro-2-butyne and methyl disulfide, the reaction proceeded readily in good yield to form the isomeric 1 1 adducts [i.e., cis- and trans-2,3-bis(methylthio)hexafluoro-2-butene in equal mole ratio], but the formation of the methylthio adducts with hexafluorobutadiene was difficult (9). This agrees with the previous alkyl disulfide and the terminal olefinic bond reaction (Eq. 2, where k, /k2 [RSSR] is relatively large) proceeding to a very poor yield of the adduct (10) ... 

Isomerization of 2-butyne-1,4-diol. In the presence of this catalyst, 2-butyne-l,4-diol isomerizes to butyrolactone. RuH2[P(C6H5)3]3 is somewhat less active.2... 

The hydroarylation of such acetylenic ketones as 3-butyn-2-one 26 poses no problems. In these cases nearly complete E-selectivity was observed, because of isomerization of the kinetically formed Z compounds [2, 4]. Four different electron-rich arenes, ArH, were shown to react smoothly, affording products 27 in yields of 77-96%. 

Boitiaux et al. (61) have examined the influence of palladium sulfuration on the hydrogenation and isomerization of 1-butene, 1,3-butadiene, and 1-butyne. The tested catalysts have been sulfided with thiophene to obtain an atomic ratio (sulfur per surface palladium) varying between 0 and 0.5. The thiophene in heptane solution is put in contact with the reduced palladium catalyst at 50°C, under 2 MPa hydrogen pressure. The butane evolution is followed during the sulfiding step (see above) and a control of total sulfur adsorption is performed by the analysis of the heptane after the sulfiding step and through X-ray fluorescence after the reaction step. 

The primary source of isoprene today is as a by-product in the production of ethylene via naphtha cracking. A solvent extraction process is employed. Much less isoprene is produced in the crackers than butadiene, so the availability of isoprene is much more limited. Isoprene also may be produced by the catalytic dehydrogenation of amylenes, which are available in C-5 refinery streams. It also can be produced from propylene by a dimerization process, followed by isomerization and steam cracking. A third route involves the use of acetone and acetylene, produced from coal via calcium carbide. The resulting 3-methyl-butyne-3-ol is hydrogenated to methyl butanol and subsequently dehydrogenated to give isoprene. The plants that were built on these last two processes have been shut down, evidently because of the relatively low cost of the extraction route. 

Reaction of Fe3(CO)12 with 3-pentyn-l-ol gives the hydrido cluster 4, formed by coupling of an allenylidene unit with a coordinated carbonyl ligand and methoxy group. In contrast, reaction with the isomeric alkyne 2-methyl-3-butyn-2-ol affords a binuclear iron complex.18 Treatment of Fe3(p3-S)2(CO)9 with Me3NO affords the vinylferrocene complex 5, whereas the similar reaction with Fe3(p3-Te)2(CO)9 gives no cluster products.19... 

In an alternative route to such molecules, Cargill and Crawford demonstrated that the photocycloadduct of cicyclo[4.3.0]non-l(6)-en-2-one (474) and 2-butyne, ie., 475, was subjected to acid-catalyzed isomerization with formation of 476.409)... 

The organozinc reagent derived from 3-bromo-l-butyne which has the allenic structure (XLII) affords a mixture of three isomeric alcohols upon reaction with diisopropyl ketone, indicating the strong tendency of rearrangement in the systems (171). The proportion of allenic alcohol... 

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