[phth]

Is there an alternate route from this sm->pdt specifically?  Can anyone think of an enolate route?  Last step: would Schlosser base work better than RMgBr?

[kriggy]

Please can you turn the picture 180°? Its very hard to read
Why dont you do the enolate adition of methylpropene moiety 1st to cyclohexanon and then grignard reaction to get the product?

[OrgXemProf]

Initial Bamford-Stevens reaction should lead to cyclohexene, but I'm somewhat hesitant about the possibility of further reaction with a second equivalent of t-BuLi to form a vinyllithium. Maybe in the presence of added TMEDA or HMPA?

A simple alternative: First step, MeMgBr + cylohexanone followed by aqueous acidic workup to afford 1-methylcylohexanol. This tertiary alcohol when heated with acid should undergo E1 elimination (Zaitsev rule) to afford 1-methylcyclohexene.

The lack of elegance attendant with the alternative route is partially compensated by its simplicity.

[k1mng]

I find compounds with ring structures a struggle to determine synthetic routes towards because there always seems to be the issue of stereoselectivity in certain steps. To generate the stereocenter with the 2-methyl propylene substituent, probably would need to use some enantioselective enolate-type chemistry. Perhaps use an enantioselective Lewis base (catalytic) e.g. proline or some other secondary amine catalyst to make the enamine in situ (enolate analogue), and react that with an appropriate substrate containing the 2-methyl propylene backbone?

Also, I was thinking that maybe some allyl cation chemistry would be awesome in this case - the 2-methyl allyl acetate would be an ideal substrate for a Pd catalyst with an appropriate chiral ligand for enantioselectivity.

Grignard reaction would be best left to last to keep our ketone functionality (and looks like it'll work fine, Schlosser's base isn't necessary) - quick conformational analysis suggests that the Grignard should selectively form the product with the methyl and 2-methylpropenyl substituents cis.

I hope this helps somewhat!

[phth]

Kriggy: oops, my bad.  I got marked wrong for that route.  OrgXemProf:I got the idea for the Bamford stevens the variant is called Shapiro Rxn.  k1mng: E1 seems like very viable.  Thanks for the responses!