Methylenecyclohexanes from methylcyclohexene

Fig. 17. Preferred conformations of the transition state which yields the half-hydrogenated state from a 4-substituted methylcyclohexene and a methylenecyclohexane.

This process is synthetically important because a sacrificial alkene such as 1-decene or 1-hexadecene can be added to bias the overall reaction toward a specific target alkene. Mechanistically, thermal isomerization apparently involves a series of reversible elimination reactions of borane followed by re-addition in an anti-Markovnikov manner.2 If the sacrificial alkene has a significantly higher boiling point, then the desired alkene can he distilled from the reaction medium.22a xhe sacrificial alkene must not boil < 160°C, however, which is the temperature required for borane isomerization. This process makes it possible to isomerize the double bond of an alkene to a less substituted isomer, a process that Brown termed contrathermodynamic isomerization.29,30 methylenecyclohexane (41) was prepared from 1-methylcyclohexene by... 

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