Cyclohexene from methane

Other methods for the preparation of cyclohexanecarboxaldehyde include the catalytic hydrogenation of 3-cyclohexene-1-carboxaldehyde, available from the Diels-Alder reaction of butadiene and acrolein, the reduction of cyclohexanecarbonyl chloride by lithium tri-tcrt-butoxy-aluminum hydride,the reduction of iV,A -dimethylcyclohexane-carboxamide with lithium diethoxyaluminum hydride, and the oxidation of the methane-sulfonate of cyclohexylmethanol with dimethyl sulfoxide. The hydrolysis, with simultaneous decarboxylation and rearrangement, of glycidic esters derived from cyclohexanone gives cyclohexanecarboxaldehyde. 

As in the [22]porphyrin(3.1.3.1) series, the cyclohexene moieties being part of the bridges originate from the preparation of the dimers from dimethylpyrrole and a hydronaphthalene diketone by acid-catalyzed condensation. The synthetic approach developed by Franck2b has the advantage over the foregoing method that more stable conventional pyrroles and dipyrryl-methanes can be used to form the macrotetracycle in a stepwise manner. 

The thermal decomposition of diazo(phenylsulfonyl)methane 223 under a nitrogen atmosphere generates phenylsulfonylcarbene which is trapped by olefin such as cyclohexene to give norcaranes 224 and 225 (equation 138)132. No cycloheptatriene derivative is isolated from the thermolysis of223 in benzene133. In contrast, intramolecular insertion of sulfonylcarbenes into a benzene ring is observed in the thermolysis of 226 (equation 139)134. 

The di-ji-methane reaction results in a 1,2-shift in a 1,4-diene unit, but such shifts sometimes occur in monoalkenes (2.44, and the mechanism must be different. The substrates are usually tetra-substituted ethylenes, and it is suggested that the reactive excited state is a Rydberg singlet state, which rearranges initially to give a carbene. Support for such a mechanism comes from the structures of products obtained from 1,2-dimethy(cyclohexene (2.45), which are... 

Thermal decomposition of 1-butene provides a more complex product spectrum than is obtained from either cis- or trans-2-butenes. Between 550° and 760°C in a flow system with nitrogen dilution (3), methane, propylene, butadiene, and ethylene were major products as well as hydrogen, ethane, 1-pentene, 2-pentene, 3-methyl-1-butene, and 1,5-hexa-diene. In studies in a static system (4), cyclohexadienes, benzene, cyclopentene, cyclopentadiene, toluene, orthoxylene, and cyclohexene were observed among the liquid products of the reaction over the temperature range 490°-560°C. 

The various radicals produced can all abstract an allylic hydrogen from the organic substrate, cyclohexene in this case. With BDEs of 372kJ/mol, allylic C-H bonds are considerably weaker than regular alkyl-H bonds, whose dissociation energies vary from about 404 kJ/mol for a tertiary C-H bond to as high as 439 kJ/mol for methane. Allylic hydrogen abstraction is shown below for the benzoyloxy radical, a major radical species in the system ... 

Figure 1.4 Microreactors with sputter-deposited catalysts (a) chip (63 X 25 mm) with Ag film for oxidative dehydrogenation of 3-methyl-2-buten-1-ol to aldehyde (464 °C) (b) chip (3x1 cm) containing Pt, Fe or Co for (de)hydrogenation of cyclohexene (up to 250°C) and synthesis gas methanation (up to 300°C). Reprinted from [31], Copyright 2004, and [35], Copyright 2003, with permission from Elsevier.

---