[Swerning]

Hi, I'm trying to protect an hydroxyl group on a ring as its silyl ether (TBS group), but i'm having no joy, also the hydroxyl group has a small alkenyl chain alpha to it and they are cis to one another

I tried the standard reaction of TBDMSCl, imidazole, DMF but this just gave unreacted starting material. I was thinking instead to try TBDMSCl, Et3N and DMAP or use the more reactive TBDMSOTf.

Any thoughts??

[Dan]

I had a stubborn neopentyl OH I wanted to silylate a few months ago. I got my best yields using TBDMSCl and using pyridine as the solvent/base, stir at RT overnight. I don't like imidazole because it's a pain to get rid of.

A post doc in the group had a very stubborn OH which me managed to protect by using something like 3 eq TBDMSCl, 5 eq imidazole, very concentrated in DMF and heated to 100 degrees C.

[movies]

As you suggested, DMAP is a good additive here.  Silyl triflates are okay, but they sometimes cause some other problems depending on what else you have in your molecule.

A guy in our lab had some crazy conditions with TBSCl and AgNO₃.  He swore by them!

[wintermute]

see this milkshake's post
http://orgprepdaily.wordpress.com/2007/03/16/notes-on-lousy-reactions/