5-Decyne reduction

Now let s draw the forward scheme. The 3° alcohol is converted to 2-methylpropene using strong acid. Anti-Markovnikov addition of HBr (with peroxides) produces l-bromo-2-methylpropane. Subsequent reaction with sodium acetylide (produced from the 1° alcohol by dehydration, bromination and double elimation/deprotonation as shown) produces 4-methyl-1-pentyne. Deprotonation with sodium amide followed by reaction with 1-bromopentane (made from the 2° alcohol by tosylation, elimination and anfi -Markovnikov addition) yields 2-methyl-4-decyne. Reduction using sodium in liquid ammonia produces the E alkene. Ozonolysis followed by treatment with dimethylsulfide produces an equimolar ratio of the two products, 3-methylbutanal and hexanal. 

The reduction of medium-size cycloalkynes, however, always yields considerable amounts of the less strained cis-cycloalkenes (A.C. Cope, 1960 A M. Svoboda, 1965). Cyclo-decyne, for example, is reduced almost exclusively to cis-cyclodecene. 

It is generally considered that alkylacetylenes are inert while others, especially with conjugative substituents, are active in polarographic reduction. That is, the supporting electrolyte and/or the solvent are usually reduced in preference to an alkyl-acetylene. It has been estimated that, relative to the standard calomel electrode (SCE), 3T for cyclononyne, 5-decyne, 1-hexyne, 3-hexyne and 2,2,5,5-... 

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). 

When I-halo-5-decynes are electrolyzed at carbon in DMF containing tetraalkylam-monium perchlorates [114], the yield of pentylidenecyclopentane increases dramatically (up to 60%) two other major products are 5-decyne and l-decen-5-yne. Reduction of 6-iodo-1-phenyl-1-hexyne at carbon in DMF containing TMAP affords benzylidenecyclopentane (36%) and 1-phenyl-1-hexyne (38%) however, in the presence of an added proton donor (l,l,l,3,3,3-hexafluoro-2-propanol), the yield of benzylidenecyclopentane climbs to approximately 60% [115]. 

Another method for the conversion of an alkyne to an alkene uses sodium or lithium metal as the reducing agent in liquid ammonia as solvent. This method is complementary to the Lindlar reduction because it produces trans rather than cis alkenes. For example, 5-decyne gives trans-5 decene on treatment with lithium in liquid ammonia. 

Bromo- and l-iodo-5-decyne were studied because they do not possess electroactive carbon-carbon triple bonds and therefore the electrolytic cleavage of the carbon-halogen bonds can be investigated over a relatively wide range of potentials. The reduction product distribution proved to be dependent upon the potentials employed during the... 

Iridium complex-catalyzed cyclization of an Af-arylcarbamoyl chloride with an alkyne has been reported by Tsuji and coworkers [153]. In a typical example, Af-methyl-Af-phenylcarbamoyl was reacted with 5-decyne and a catalytic amount of [IrCl(cod)]2 (2.5mol%) and additional cod (30mol%) in refluxing o-xylene for 20 h to give 3,4-dimethyl-l-methyl-2-quinolone in 92% yield (Scheme 11.5). During this reaction, no indole product formed by decarbonylation was observed. This reaction is proposed to proceed by oxidative addition of Af-arylcarbamoyl chloride to Ir(I), giving a carbamoyl chloroiridium(III) species. Subsequently, the formation of a five-membered iridacycle by ortho-aryl C-H activation followed by insertion of the alkene and reductive elimination produces the 2-quinolone derivative. 

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