Sterically hindered carbonyl on Enone (Enone + Grignard reaction)

[shaneo]

Hi all,

I am of the understanding that when a carbonyl group is in a sterically hindered environment on an enone the grignard reagent instead chooses to opt to react with the alkene group on the enone instead. (More specifically cleavage of a hydrogen atom). I have to write out a mechanism for this but i can't get to grips with it.

It would be much appreciated if someone could outline a general mechanism of a reaction of this type with the sterically hindered carbonyl group! or alternatively point me to a webpage or ebook that can! as i have scoured the web to no avail.



Thanks,

shaneo!