Methylcyclopentane carboxylation

These investigators found that the normal acids occurred in much greater abundance than the branched acids. The cyclic acids isolated by Lochte and coworkers (31) include cyclopentanecarboxylic acid, 2-methylcyclopentanecarboxylic acid, 3-methylcyclopentane-carboxylic acid, cyclopentaneacetic acid, 3-methylcyclopentaneacetic acid, 2,3-dimethyl-cyclopentaneacetic acid, 1,2,2-trimethylcyclopentanecarboxylic acid, cyclohexanecarbox-ylic acid, p-methylcyclohexanecarboxylic acid, and the cis and trans forms of 2,2,6-tri-methylcyclohexanecarboxylic acid. In addition, Lochte and coworkers (31) isolated dimethylmaleic anhydride, which has also been isolated by Nenitzescu and coworkers (42). 

Ring contraction. Cyclohexene added dropwise at 10-12° during 55 min. from a syringe to AggO in 98%-H2S04 under 1 atm. CO 1-methylcyclopentane-carboxylic acid. Y 84%. - Similarly 1-Hexanol a,a-dimethylpentanoic acid. Y 79%. F. e., also from satd. hydrocarbons, s. Y. Souma and H. Sano, Bull. Chem. Soc. Japan 47, 1717 (1974). 

Methylcyclopentane tert. Butanol 15-25 46% 1-Methylcyclopentane-carboxylic acid-1 7 % Pivalic acid... 

The formation of C6 and C7 acids along with some ketones was reported in the reaction of isopentane, along with methylcyclopentane and cyclohexane with CO in HF-SbF5 at ambient temperatures and atmospheric pressure.406 Yoneda et al.407 have also found that other alkanes can be carboxylated as well with CO in HF-SbF5. Tertiary carbenium ions, which are produced by protolysis of C—H bonds of branched alkanes in HF-SbF5, undergo skeletal isomerization and disproportionation before reacting with CO. Formation of the tertiary carboxylic acids in the... 

The HF-SbFs system works well in the Gattermann-Koch formylatlon of arenes and the Koch carbonylation of alkanes [54]. For instance, biphenyl is diformylated in HF-SbFs-CO to afford 4,4 -diformylbiphenyl as a major isomer (Scheme 14.20). The carbonylation of alkanes with C5-C9 carbon atoms in the HF-SbFs-CO system affords mixtures of C3-C8 carboxylic acids after hydrolysis of the generated secondary carbenium ions [55]. Successive treatment of methylcyclopentane with CO in HF-SbF and with water produces cyclohexanecarboxylic acid as a major product (Scheme 14.21) [56]. It seems that a tertiary methylcyclopentyl cation readily isomerizes to the more stable cyclohexyl cation before being trapped by CO. Bicyclic a, -unsaturated ketones are functionahzed by HF-SbF or FSOsH-SbFs under a CO atmosphere to give saturated keto esters after methanolysis (Scheme 14.22) [57]. Alcohols with short carbon chains also react with CO in HF-SbFs to give the corresponding methyl esters [58]. y-Butyrolactones are carboxy-lated under the same conditions to afford 1,5-dicarboxyhc acids [59]. 

The formation of Cg or carboxylic acids along with some ketones was reported in the reaction of isopentane, methylcyclopentane and cyclohexane with CO in HFiSbFg at ambient temperatures and atmospheric pressures. ... 

An interesting example of thermodynamic vs kinetic control was observed in the temperature dependence of carboxylation of methylcyclopentane in the presence of HF-SbFs (90). Carboxylations were carried out by bubbling CO through the reaction mixture either at —40°C or 0°C followed by quenching the resulting solution with ethanol. A reaction at -40°C yields quantitatively ethyl... 

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