Methylcyclopentane carbonylation

The forward synthetic sequence would therefore involve the Michael reaction of 2-methylcyclopentane-l,3-dione with methyl vinyl ketone to give (20), followed by cyclisation to the hydroxyketone (19), and then dehydration to the target molecule (13a). The overall process of addition and cyclisation is known as the Robinson annelation reaction.3 In this preparative example (Expt 7.6) the methyl vinyl ketone is used directly under conditions which minimise its polymerisation 48 it should be noted, however, that many literature examples of the annelation reaction use Mannich bases or the corresponding methiodides as an in situ source of the a, /J-unsaturated carbonyl component (see Section 5.18.2, p. 801). 

The third group of cyclic compounds formed by intramolecular carbanion addition to the carbonyl group are the target molecules 5,5-dimethylcyclo-hexane-l,3-dione (dimedone, 30) and 3-methylcyclopentane-l,2,4-trione (31). 

Suitable retrosynthetic disconnections of 3-methylcyclopentane-l,2,4-trione may not be immediately obvious owing to the presence of the three carbonyl groups. However, disconnection in the manner shown gives the reagent equivalents diethyl oxalate and butan-2-one. 

After evacuation, standard vacuum techniques are used to measure and condense equimolar amounts (20 mmoles each) of carbonyl fluoride and oxygen difluoride into the cylinder. The cylinder should be equipped with an explosion rupture assembly and should be in a shielded location before it is allowed to warm up. The valve is then closed, and the cylinder and its contents are allowed to warm to room temperature and remain at that temperature for 5 days. After this time, the cylinder contents are passed through a trap kept at approximately — 140°C. (melting Skelly-Solve F or methylcyclopentane). 

Carbonyl-derived RhCo bimetallic catalysts exhibit high selectivity toward skeletal rearrangement of methylcyclopentane (MCP) (to a mixture of 2- and 3-methylpentanes), whereas on the conventional counterpart hydrocracking... 

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]. 

Methyl methacrylate (MMA) carbonylation by, 234, 245-248 chemistry, 245-248 derivatives, 248 oxidation by, 130 Methyl phenol carbinol, 14 Methyl-tert-butyl ether (MBTE), 146, 150, 154 Methylamine, 231 Methylcyclopentane, 202... 

Protolytic ionization of methylcyclopentane gives an equilibrium mixture of the tertiary 1-methyl-1-cyclopentyl cation (29) (more stable by about 40 kJ/mol) and the secondary cyclohe l cation (32) (Scheme 5). At low temperature, irreversible reaction of 29 with CO leads to ion 30, which, after reaction writh ethanol, gives the 31 ester. Product composition, in this case, reflects the difference in stability of the intermediate carbocations. Since the carbonylation step is reversible at higher temperature, and carbocation 32 has a much higher affinity for CO, the concentration of 33 in solution continuously increases to yield, after quenching with ethanol, the 34 ester. This is an example of a kinetically controlled product formation through a thermodynamically unfavorable intermediate. 

One recent example of this is the carbonylation of methylcyclopentane in HF-SbFs solutions. An array of fascinating reactions occurs upon protonation of an alkane, and they are illustrated in the following scheme. The relative basicity of a bonds in alkanes is 3° C-H > C-C > 2° C-H >> 1° C-H. Hence, the protonation of methylcyclo-... 

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