Octynes isomerization

The action of the complex 570 on various alkynes gives diverse products ethyl propiolate affords a mixture of all three possible triethyl benzenetricarboxylates, phenylacetylene yields mainly the trans-QnyviQ 571 3-hexyne behaves similarly, but 1-octyne isomerizes to 2-octyne . The palladacyclopentadiene 572 catalyses the co-trimerization of hex-3-yne... 

The thiotelluration of 1-octyne requires prolonged photoirradiation, giving rise to an isomeric mixture of products in moderate yields. This result depends on the different stability of the two vinylic radicals. 

The study of Tables I and II has revealed the fact that isomerization of a normal paraffin to an isoparaffin produces certain specific and characteristic changes in the physical constants as the methyl group is moved from point to point along the chain. In a paper presented before the Refining Division of the American Petroleum Institute in November 1942, attention was called by this author to alternation in the melting points of the n-octenes and n-octynes as the point of unsaturation is moved from position 1 to 2 to 3 to 4 (5). Now that the cis-trans pairs have been separated and more highly purified, the alternation remains characteristic of both forms, although the data on the cis forms are not fully verified. 

Carbometalation of silylalkynes. In the presence of this nickel-aluminum catalyst, methylmagnesium bromide adds to 1-trimethylsilyI-l-octyne (1) to give the cis-addition product 2, which isomerizes slowly to 3, The use of ethylmagnesium bromide results in reduction mainly to cis-1 -trimethylsilyl-1 -octene. The products 2 and 3, as expected, react with a variety of electrophiles to give di- and trisubstituted... 

This catalyst (1) is a selective catalyst for hydrogenation of 4-octyne to cw-4-octene (90% yield). If the product is left in contact with 1, it isomerizes to the trans-isomer. Since monoalkenes are hydrogenated slowly with this catalyst, cyclo-octene can be obtained from either 1,3- or 1,5-cyclooctadiene. Of more interest, benzene can be hydrogenated to cyclohexane (83% yield). One drawback is that the catalyst loses about 90% of its activity after one cycle. 

The base-induced dehydrohalogenation of vinyl halides and allyl halides often gives low yields of allenes because of the competing reaction to alkynes alkynes can either be formed by direct elimination from vinyl halides or by isomerization of the allene first formed to the isomeric alkyne. Since it has been established that anti elimination of hydrogen halide from vinyl halides to yield alkynes is much faster than syn elimination, the proper choice of the starting material is often important for a successful allene synthesis. When ( )-4-bromo-4-octene was treated with NaOMe, the sole product was 3,4-octadiene, whereas the conesponding Z-educt yielded 4-octyne (Scheme 66). ... 

When 4-octyne (CH3CH2CH2-C=C-CH2CH2CH3) is added to n-propylamine (CH3CH2CH2NH2), two enamines result. This can be accounted for on the basis of Z-E geometric isomerism. The two isomers may be written as follows ... 

Hydroboration of terminal alkynes, e.g. 1 -hexyne, 1 -octyne or cyclohexylacetylene, with a dialkylborane, such as bis(l, 2-dimethylpropyl)borane, followed by copper(I)cyanide and copper(II) acetate in HMPA containing a trace of water, gives isomerically pure ( )-l-cyanoalk-l-enes (equation 29)133. Successive treatment of 1-bromo-l-alkynes with dialkylboranes and sodium methoxide results in the borinate esters 208, which are converted into ( )-alkenes of greater than 99% isomeric purity by protonolysis. The action of alkaline hydrogen peroxide on the borinates produces ketones (equation 30)134. 

Moving the triple bond towards the center of the alkyne substantially increases the relative abundance and hence stability of the corresponding molecular ion (Figure 2). With the isomeric octynes the fragmentation yields (total fragment ion current divided by [M ]) are 125 for 1-, 6.3 for 2-, 2.1 for 3- and 0.77 for 4-octyne. Analogous, albeit not as profound, trends were observed at 70 eVk Thus, determination of the fragmentation yield of isomeric alkynes suffices to ascertain the position of the triple bond". ... 

Fe(CO)5] to form a Fe(alkyne)+ complex on CAD, the latter produces structure-indicative fragments, based on which the position of the acetylenic bond can be determined ". This is illustrated for isomeric octynes in Figure 16 ". ... 

C24K is a moderately active catalyst for hydrogenation of alkenes. It is a very efficient catalyst for isomerization of cw-stilbene to trcnj-stilbene. It is also effective for isomerization of alkynes 2-octyne-> 1-octyne (86% yield). An allene is a probable intermediate 2-decyne -> 1-decyne (207o) and 1,2-decadiene (9%,). Potassium alone also effects these isomerizations, but only at higher temperatures. Benzene is slowly converted into biphenyl when in contact with C24K in refluxing cyclohexane. This reaction has also been reported for CgK in DMF at 20 (61%, yield).=... 

On the other hand, Yamamoto and co-workers observed that the Pd-catalyzed reaction of o-bromobenzaldehyde (71) with 4-octyne in DMF using Pd(OAc)2 gave rise to the indenol 74 in 71 % yield. Also it was conhrmed that the indenol 74, once formed, was isomerized to the indanone 75 quantitatively in the presence of Pd(OAc)2 and AcOK [24]. Furthermore, reaction of o-bromoacetophenone (76) with 4-octyne afforded the substituted indenol 77 in 82% yield, which has no... 

Carbonylation proceeds in the presence of chalcogen compounds without poisoning Pd catalysts. Pd-catalyzed stereo- and regioselective carbonylative double thiolation of 1-octyne with diphenyl disulfide (3) afforded the (Z)-j6-(phenylthio)--unsaturated thioester 4 [2], The thioester 4 can be converted to 3-(phenylthio)-2-alkenal 5 by Pd-catalyzed reduction with HSnBu3 under mild conditions [3]. When propargyl alcohol was subjected to the carbonylation in the presence of either diphenyl diselenide (6) or disulfide 3, 3-phenylselenobutenolide 7 or 3-phenylthiobutenolide was obtained. The transformation involves isomerization of the acylpalladium intermediate 8 to 9 [4]. 

Hydrothiolation of 1-alkynes with thiols gives vinyl sulfides with high regio- and stereoselectivities. Reaction of 1-octyne with benzenethiol catalyzed by Pd(OAc>2 gave the Markonikov-type product 110. Isomerization of the double bond occurred and the isomer 111 was obtained when PdCl2(PhCN)2 was used [34]. 

It was reported that the pyrazolyl-borate complex of rhodium (Tp Rh(PPh3)2, Tp =hydrotris(3,5-dimethylpyrazolyl)borate) is active not only in the hydrothiolation with ArS H, but also with AlkS H in good to high yields of Markovnikov isomer at room temperature (Scheme 3.91) [162,163]. However the reaction of 1-octyne gave a mixture of isomers in 70% yield. In addition to the double bond isomerization, a Markovnikov/anti-Markovnikov ratio of 12 1 was found in the case of 1-octyne. 

WORKED PROBLEM 12.7 Di-rcc-butylacetylene (3,6-dimethyl-4-octyne) fails to isomerize to another alkyne when treated with NaNH2/NH3. Ebcplain. 

Table 35 [146]. Induction period and half-time values of isomeric n-octynes in the Ni-carbonyl-cataly ed hydrocarhoxylation under various reaction conditions...

Fig. 14 [146]. Half-time values of the hydrocarboxylation of isomeric n-octynes in dependence on the initial pressure at 200 °C in presence of catalytic amounts...

Let s start with a synthesis of racemic S-deoxy-VGEi (90) developed by the Sih group at the University of Wisconsin. The key reaction was the addition of vinyllithium 88 to the THP ether derived from enone 86. The vinyllithium reagent was prepared by hydroalumination-iodination of I-octyne (87) followed by a transmetallation. Enone 86 was prepared in two steps from cyclopentadiene and ethyl 7-bromoheptanoate. Notice that the alkylation of lithium cyclopentadienide with this bromoester provided I-substituted cyclopentadiene 84 in quantitative yield. The isomerization that had to be avoided in the Corey lactone approach was a necessary part of these tactics. 

Similar considerations allow us to tell the difference between 1-octyne and an isomeric bicyclic hydrocarbon, bicyclo[3.3.0]octane. 

The structural features present in 1-octyne and absent in the bicyclic hydrocarbon are a carbon-carbon triple bond and an sp-hybridized C—H bond. Once again, these features give rise to characteristic group absorptions, and 1-octyne has them and the isomeric bicychc hydrocarbon does not. 

The sp -hybridi2ed C—H bonds in saturated hydrocarbons such as octane (Figure 2.10a) absorb infrared radiation in the 2850—3000 cnr region. The sp -hybridized C—H bonds in alkenes such as 1-octene absorb energy at 3080 cnr . This peak appears separately from the absorptions associated with the sp -hybridized C—H bonds in this molecule (Figure 2.10b). The isomeric cyclooctane would not have the 3080 cm" absorption. An sp-hybridized C—H bond in a molecule such as 1-octyne (Figure 2.10c) absorbs infrared radiation at 3320 cm". An isomeric bicyclic hydrocarbon with no multiple carbon-carbon bonds, and hence no sp - or sp-hybridized carbon atoms, would have absorptions only in the 2850-3000 cm" region. 

The reaction of Pd(OAc)2 with 3 equiv of PhSH in THF-t/g immediately gave dark brown precipitates and ca. 2 equiv of AcOH. This precipitate scarcely exhibited the catalytic activities for the addition of PhSH to 1-octyne. On the other hand, the precipitates prepared in the presence of 1-octyne had a moderate catalytic activity. cw-Addition of PhSH to 1-octyne was confirmed by the reaction employing 1-octyne-i-J. The ( )-isomer, ( )- -C6Hi3(PhS)C=C(D)H, is the kinetic product and gradually isomerized to the (Z)-isomer. A mechanism similar to that shown in Scheme 6 was proposed [22]. 

To ascertain the stereochemistry of this Pd(OAc)2-catalyzed hydrothiolatiOTi of terminal alkynes, the reaction of PhSH with 1-octyne-l-d (containing 93% d) is monitored by H NMR spectroscopy. The E Z ratio of the thiolation products is 100 0 at the initial stage, and then -isomer as the kinetic product gradually isomerized to Z-isomer. These results clearly indicate that the hydrothiolation proceeds via yn-addition at least at the initial stage (Scheme 4). 

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