[jayashae]

Studying for another midterm for monday and this problem on past exam is confusing me.



so for the bottom of the ring, I think it's some form of nucleophilic attack on a brominated propane turned eventually into a dimethyl ketone and undergoes a grignard reaction with the main molecule.

as for the top, I think it's some sort of aldol condensation but I'm not really sure?  any helpful hints or guidelines would be much appreciated, my exam is tomorrow.


Thanks!

[discodermolide]

I would reduce the aldehyde to the alcohol, brominate the alcohol and make I phosphonium salt and do a Wittig reaction, this puts the double bond in place.
As you said make acetone from propane, make the Grignard and react with the acetone.
The Grignard I would do after reduction of the alcohol.
I hope that's clear enough

[jayashae]

omg thanks for the quick input! can you elaborate on the part about bromination of the alcohol and make I phosponium salt?  little unfamiliar with the mechanism

[jayashae]

The Grignard I would do after reduction of the alcohol.

hmm, if I leave the grignard to the end, wouldnt the Br's on both side of the molecule do the grignard?

[discodermolide]

omg thanks for the quick input! can you elaborate on the part about bromination of the alcohol and make I phosponium salt?  little unfamiliar with the mechanism

This is the Wittig reaction, see picture

[discodermolide]

The Grignard I would do after reduction of the alcohol.

hmm, if I leave the grignard to the end, wouldnt the Br's on both side of the molecule do the grignard?

You must figure out an order of steps, obviously what you said will happen.
I just gave you some thoughts on a possible synthesis in no particular order.

by the way if you have acetone made you can use it to protect the alcohol before the Grignard.