Hexyne isomers

Alkynes react with mercuric acetate in acetic acid to give addition products. In the case of 3-hexyne, the product has -stereochemistry, but the Z-isomer is isolated from diphenylacetylene. The kinetics of the addition reaction are first-order in both alkyne and... 

Examples of perfluoroalkyl iodide addition to the triple bond include free radical addition of perfluoropropyl iodide to 1 -heptyne [28] (equation 21), thermal and free radical-initiated addition of lodoperfluoroalkanesulfonyl fluorides to acetylene [29] (equation 22), thermal addition of perfluoropropyl iodide to hexa-fluoro 2 butyne [30] (equation 23), and palladium-catalyzed addition of per-fluorobutyl iodide to phenylacetylene [31] (equation 24) The E isomers predominate in these reactions Photochemical addition of tnfluoromethyl iodide to vinylacetylene gives predominantly the 1 4 adduct by addition to the double bond [32] Platinum catalyzed addition of perfluorooctyl iodide to l-hexyne in the presence of potassium carbonate, carbon monoxide, and ethanol gives ethyl () per fluorooctyl-a-butylpropenoate [JJ] (equation 25)... 

In acetic acid, both 1-pentyne and 1-hexyne give the syn addition product. With 2-butyne and 3-hexyne, the major products are p-chlorovinyl acetates of //-configuration.154 Some of the dichloro compounds are also formed, with more of the E- than the Z-isomer being observed. 

The addition of triethylsilane to 1-hexyne led to an 80/20 mixture of cis- to /raws-1-triethylsilyl-1-hexene. This is most anomalous usually, only trans isomers result by cis-addition of Si—H to the triple bond. 

Dinuclear palladium complexes catalyze m-hydroarylation of alkynes with arenes.56 The reaction of 3-hexyne with benzene in the presence of a dinulear palladium complex Pd2R2(M-OH)(//-dpfam) [dpfam = j/V,Ar -bis[2-(diphenyl-phosphino)phenyl]formamidinate, R=/>-Tol] and tri(/z-butyl)borane at 100 °C for 4h affords ( )-3-phenyl-3-hexene quantitatively (Equation (53)). The hydroarylation of 3-hexyne with monosubstituted benzenes ( )-3-aryl-3-hexenes with a 2 1 ratio of the meta- and ra -isomers. This regioselectivity is different from that of the hydroarylation of diphenylacetylene catalyzed by Rh4(GO)12.57... 

Beside the aromatic vinylidene complexes also alkyl vinylidene complexes [Ru(bdmpza)Cl(=C=CHPr)(PPh3)] (33c) and [Ru(bdmpza) Cl(=C=CHBu)(PPh3)] (33d) have been synthesized (Scheme 20), following the same procedure as earlier by using 1-pentyne or 1-hexyne. IR and NMR spectroscopic data of 33c and 33d are similar to those of 33a and 33b. Again only one major isomer was isolated in the case of [Ru(bdmpza)Cl(=C=CHPr)(PPh3)] (33c), though the... 

Indeed only alkynes could be reduced in (CH3)4N+ solutions while alkenes were inactive. Reduction of 1-hexyne, propargyl alcohol and 1,4-butyne diol were performed 13 at a mercury cathode with (CH3)4NC1 as the electrolyte. The corresponding olefins were formed and the respective yields were 45 %, 62 % and 82 %. The diacetate of 15 behaved similarly. However only the trans isomer 16 was formed from 15 while a mixture of trans and cis (6 4) isomers resulted from the reduction of the diacetate. Polarography of several alkynes in methanol with (C4H9)4N+ electrolytes showed, 3) that they react close to background decomposition. It was therefore proposed 14) that (CH3)4N+-mercury may be involved in the cathodic reduction of alkynes when (CH3)4N+ salts serve as the electrolytes. 

Cathodic reduction of disubstituted alkynes is possible but proceeds with relatively low current efficiency. Reduction of 4-octyne under similar conditions as used for 1-hexyne yields only 50% 4-octene after transfer of 8 F mol-1. It is interesting to note that the ratio trans/cis for the cathodically obtained 4-octene was 3/l. Other methods29 involving electron-transfer reductions yield the corresponding trans isomers almost exclusively. 

Similar irradiation of 34 and p-tolylpentamethyldisilane with 1-hexyne or trimethylsilylacetylene in benzene leads to the formation of ( )-olefins in moderate yields (89). In no case are (Z)-isomers detected. The quenching capacity of the acetylenic compounds, however, seems lower than... 

The hydrosilation of 1-alkynes can give either Z-or E-isomers (see (E) (Z) Isomers) of the linear vinylsilane or the Markownikow product (equation 5). Reaction of 1-hexyne with trichlorosilane under platinum catalysis conditions gives a mixture of 1- and 2-silyl-l-hexene (78 22). From the E-stereochemistry of the 1-silyl isomer, a yyn-addition mechanism can be assumed. 

Hexyne is best suited to study activity and selectivity of a hydrogenation catalyst. A mixture of 1,10-phenanthroline-stabilized seven- and eight-shell Pd clusters (Pd 7/8) on Ti02, dispersed in ethanol, catalyzes the transformation of 2-hexyne to cA-2-hexene with ca. 95 % selectivity and a turnover frequency (TOF) of 35 min . As can be seen from Figure 2, tranx-2-hexene, n-hexane, and other hexene isomers are only formed in consecutive reactions. If the phenan-... 

The benzylation reaction of 3-hexyne with benzyl chloride was reported to give a mixture of cis and trans addition compounds and 2,3-diethylindenone (equation 124). ° It was found that in high polarity solvents the yield of the trans addition compound and of the indenone increased. An ionic mechanism was suggested to account for the trans addition compound, and a more covalent complex or ion pair to account for the cis isomer. 

The coupling reaction between sp - and ip-carbon centers is stereospecific with (Z)- and ( )-vinylic bromides. For example, (Z)-methyl-3-bromoacrylate reacts with 1 -hexyne in the presence of a Pd catalyst to form the (Z)-enzyne as the only product (Scheme 24). This technique has also been applied in the stereoselective synthesis of 1 -chloroenynes from (Z)-dichloroethylene (Scheme 25). Trimethylsilylacetylene affords the 2 1 coupled endiyne product (37) in a stereospecific manner on coupling with geometrical isomers of 1,2-dichloroethylene (Scheme 26). In the absence of copper(I) iodide, no reaction occurs. ... 

Fig. 6.33. Possible isomers from the hydrosilylation of 1-hexyne (adapted from...

The P-acetylenic alcohol, 3-hexyne-l-ol, also reacted with the P=N species via addition of the 0-H moiety. In this case, however, the next step is a simple proton migration from nitrogen to phosphorus to give the P-H bonded P isomer. Similar addition-migration processes are found in the reactions of the two-coordinate phosphinimine with simple aliphatic alcohols (5). 

Furoxans have appeared rather unexpectedly in two nitrosoacetylene reactions. Base induces dimerization of 1-nitroso-l-hexyne (54), giving butyl-hexynylfuroxan (55, or its isomer).293 With anilines, and in the presence of nitrosyl chloride used in its preparation, the nitroso compound 54 formed arylaminofuroxans (56).294 The structure of one of these (56 Ar = p-BrC6H4) was proved by X-ray crystallography.53... 

The formation of benzoquinones from alkynes and the cobalt complex 595 proceeds with moderate regioselectivity e.g. 1-hexyne affords the isomers 596 and 597 in the ratio 4 ... 

Cobalt metal catalyses the co-trimerization of one molecule of acetonitrile with two of 1 -pentyne or 1 -hexyne to yield mixtures of the pyridines 610 and 611 (R = Pr or Bu). The regioselctivity of the reaction of nitriles with terminal acetylenes has been investigated. It was found that, in general, mixtures of 2,4,6- and 2,3,6-trisubstituted pyridines are produced. The selectivity depends on the size of the substituents attached to the triple bond and the cyanide group. If either of these is large, only 2,4,6-substituted pyridines are obtained. Ethyl propiolate and aliphatic or aromatic nitriles (RCN) yield, in addition to the usual type of product, i.e. 612 and 613, the 2,3,5-isomer 614. Pyridines 617 result from the action of alkynes RC=CH (R = Ac, PrCO or C02Me) on the electron-rich... 

Deuterium labeling corroborates the migration of a j5-H atom. If no j5-hydrogen is available after propargylic insertion (as, e.g., in 3-hexyne or 2-pentyne), the Fe+ ion either catalyzes interconversion to an isomer which possesses a j5-H atom (3-hexyne 2-hexyne),... 

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