Octyne reduction

Asymmetric reduction of a, -acetylenic ketones 2 Detailed directions for reduction of l-octyne-3-one to (R)-l-octyne-3-ol with this reagent are available. This method has been used to reduce 10 other acetylenic ketones in >70% ee. 

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. 

B. The flask 1s cooled to 0°C (ice bath) and 35.3 g (0.285 mol) of 1-octyn-3-one (Note 5) is added. After an initially exothermic reaction, the reaction is allowed to warm to room temperature. The reduction can be monitored by gas chromatography (Note 6), but generally 8 hr is required for completion. The color of the reaction mixture is initially light yellow and darkens to red at the end of the reduction. 

The most popular methods of preparing optically active l-octyn-3-ol involve asymmetric reduction of l-octyn-3-one with optlcally-active alcohol complexes of lithium aluminum hydride or aluminum hydride. These methods give optical purities and chemical yields similar to the method reported above. A disadvantage of these metal-hydride methods is that some require exotic chiral alcohols that are not readily available in both enantiomeric forms. Other methods include optical resolution of the racemic propargyl alcohol (100 ee) (and Note 11) and microbial asymmetric hydrolysis of the propargyl acetates (-15% ee for l-heptyn-3-ol)... 

Alternatively, lithium/ammonia reduction of 4-octyne, followed by addition of HBr, gives 4-bromooctane. 

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... 

In the initial studies by Campbell and Eby it was noted that 3- and 4-octyne, 3-hexyne and 5-decyne could be efficiently reduced to the corresponding rram-alkenes in good yields and with remarkably high stereoselectivity. Shortly thereafter, Henne and Greenlee reported the quantitative reduction of 1-alkynes to 1-alkenes using sodium in ammonia in the presence of ammonium ion. In the absence of ammonium ion, however, extensive metallation of the 1-alkyne occurs. In the presence of ammonium ion dialkylacetylenes are inefficiently reduced (extensive hydrogen evolution occurs, in which sodium is consumed). 

Benkeser et al. have reported that the reduction of 3- and 5-octyne with lithium in ethylamine at -78 °C produces the corresponding rran -alkenes in good yield. At 17 "C, however, overreduction of the alkene can occur if excess lithium is present. ... 

Sih (38) has described the reduction of E-l-iodo-l-octen-3-one with Penicillium decumbens to give the desired S-alcohol. Based on optical rotation, the e.e. was about 80%, An asymmetric chemical reduction of this same ketone, using lithium aluminum hydride that had been partially decomposed by one mole each of S-2,2 -dihydroxy-l,T-binaphthol and ethanol (42), gave the desired alcohol in 97% e.e. This reagent also reduced l-octyn-3-one in 84% e.e. to the corresponding alcohol (43). A 92% e.e. could be obtained with B-3-pinanyl-9-borabicyclo[3.3.1]nonane as the reducing agent (44). 

The first attempt to prepare dialkyl 1-aIkynyIphosphonates by a Michaelis-Becker reaction was reported in 1965, " Only octyne is produced when 1-bromooctyne is allowed to react with sodium diethyl phosphite in liquid ammonia, the coproduct being diethyl phosphoramidate. It seems likely that reduction of the bromo compound occurs by a halogen-metal exchange, with the resulting diethyl bromophosphate being immediately converted into diethyl phosphoramidate by the hquid anunonia. ... 

This polyamide was also used to support a palladium catalyst for the selective reduction of alkynes and dienes.209 Phenylacetylene was reduced to styrene in 100% yield and 100% conversion. The reduction of 1-octyne was 80% selective to 1-octene at 100% conversion. There was no loss in activity or selectivity after 11 successive runs. A polymeric analogue of triphenylphosphine (5.49) has been used to immobilize rhodium dicarbonylacetylacetonate for the hydroformylation of 1-octene to the corresponding aldehyde (5.50).210... 

Reaction (d) occurs for terminal alkynes (R = H), 1-hexyne, 1-octyne and phenyl acetylene (80-98%), with no further reduction to alkanes . The internal alkynes, 2-hexyne and diphenylacetylene, give exclusively cis-alkene (80-95%) ". However, the organometallic intermediates of Eq. (d) may contain Cu—C rather than Mg—C bonds. 

In reactions with aliphatic alkynes, such as CH3(CH2)5C CH, besides the addition-elimination product, CH3(CH2)5C=CRf, a reduction product CH3(CH2)5CH=CHRf was also formed, whereas with 4-octyne the only product isolated was CH3(CH2)2C(Rf)= CH(CH2)2CH3156. 

The other major body of work relating to catalytic hydrogenation in the liquid phase is due to Sokol skii and co-authors. In a succession of papers he reports studies of the hydrogenation of 3-butyn-l-ol on Pd at open-circuit and controlled potentials, a number of alkynes" such as hexyne and octyne, the effect of alkali-metal cations, the hydrogenation of DMVC on Pd as a function of composition open circuit and driven hydrogenation of furfural and furfuryl alcohol at a Pd-Pt surface and most recently Ni catalysed reduction of pyridine. In the more recent of these papers the use of product analysis methods affords a further insight into the process and... 

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]. 

Although mechanistically different, functionalized alkenylsilanes are prepared stereoselectively by the reaction of 1-alkynes with iodotrimethylsilane (123) and diethylzinc. At hrst oxidative addition of 123 to Pd(0) generates 125. Then insertion of 1-octyne to 125 affords the alkenylpalladium 126. Transmetallation with Et2Zn gives 127 and reductive elimination provides the alkenylsilane 124. The reaction can be regarded as a Heck-type reaction of alkyne with MesSi-I, followed by Negishi coupling [37]. 

Dissolving metal reductions works very well with aldehydes and ketones, but alkenes are not readily reduced under the same conditions. For example, 1-hexene is reduced to hexane in only 41% yield with Na/MeOH/liquid NHg.14 Alkynes, on the other hand, are reduced to alkenes in good yield using dissolving metal conditions, and the experimental evidence shows that the -alkene is the major product. In a typical example, 4-octyne (60) is treated with sodium in liquid ammonia, and oct-4 -ene (64) is isolated in 90% yield. None of the Z-alkene is observed in this reaction. The reaction with sodium in liquid ammonia is an electron transfer process similar to that observed with ketones and aldehydes, but how is the E geometry of the alkene product explained ... 

With Ni° as a catalyst, an intermolecular [4+2] cycloaddition [45] reaction with cyclobutanone 52 and 4-octyne 53a produced cyclohexenone 54a in 95% yield. The proposed reaction mechanism is illustrated in Scheme 9. Presumably the reaction of 52 and 53a with Ni° would proceed through oxidative cyclization to give oxanicke-lacyclopentene (55). P-C elimination cleaves the cyclobutane ring to generate 56 and leads to formation of product 54a after reductive elimination. Overall, a formal [4+2] cycloaddition was accomplished with Ni° via p-C elimination. In contrast, Rh was not an effective catalyst for this transformation. 

Other reactions studied include reduction of the triple bond of a-acetylenic esters and nitriles by tributyltin hydride in methanol electroreductive cyclization of acetylenic halides at a mercury cathode the trimerization and tetramerization of cyclo-octyne in the presence of various transition metals the kinetics of bromination of alka-l,3-diynes, of permanganate oxidation of acetylenedicarboxylic acid, and of iodination of propiolic acid the participation of the triple bond in reactions of various acetylenes of the general formula (225) and the trimerization of but-2-yne with tolyl-palladium chloride to give a [Pg.48]

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