[rentj]

i am wondering if i have a bromo substituent at the end of an unsaturated trans compound, where the other end is an aldehyde. if i put magnesium metal to make a grignard reagent of it, will it cyclize? the 'carbanion' will attack the aldehyde to form an alcohol, but what happens to the c=c double bond? in a cyclic molecule, the c=c bond has to be cis. if the initial molecule has a trans c=c bond, does the reaction occur? thank you.

[Borek]

Even if cyclization is possible (no idea, I am not an organiker), you will get a mixture of products, there is nothing that could stop intermolecular reaction from occurring.

[rolnor]

Six membered rings is highly favored, I think other products are very minor

[Babcock_Hall]

How does the double bond isomerize?

[rolnor]

Hi, hi, yeah, that is problematic. Taking that in consideration, polymers are absolutely possible.

[clarkstill]

No, the cyclization won't occur - we have a very similar project running in my lab at the moment but forming a lactam by Buchwald-Hartwig coupling. We're playing around with photo-isomerisation of the alkene, since in the trans configuration cyclization is impossible. Ideally you would find a way to isomerise the alkene reversibly in situ, so the cis form can be continuously trapped out by cyclization. You can also use catalytic iodine (e.g. https://uregina.ca/~eastalla/I2cistra.pdf) but it wouldnt be compatible with grignard conditions.

You could potential mask the alkene as something sp3 hybridised, then re-form it after cyclization, but the most common way would be to add HBr across the alkene - which would cause problems with selectively forming the correct grignard reagent. Perhaps hydroboration-oxidation to generate the alcohol? If the alcohol is protected, you could then cyclized, deprotect and eliminate? But elegant it aint...