alkyl groups undergo [1,5] shifts very poorly and usually require high temperatures. however, for cyclohexadienes, the temperature for alkyl shifts is not much higher than that for carbonyls, the best migratory group. a study showed that this is because alkyl shifts on cyclohexadienes proceed through a different mechanism. first the ring opens, followed by a [1,7] shift, and then the ring reforms electrocyclically: