gemar14 - 14-5-2022 at 12:37
I have protected a phenol with TIPS and am wondering if the TIPS group will survive Friedel-Crafts with AlCl3 and, say, acetyl chloride. From what I
understand, the oxygen of the OTIPS should be less nucleophilic than, say, that of anisole because of increased back-donation into a silicon sigma*
orbital. Also, the TIPS group itself is sterically bulky (I know the A value for TMS is around 2.5, so TIPS should be even bigger) which should
frustrate the formation of an adduct with AlCl3 even more. As far as I can tell, mechanistically the only worry is that IF an adduct is formed, the
chloride ion from another AlCl4- that will eventually detach from the Al can choose to either restore aromaticity in the phenyl ring or attack silicon
and deprotect. But thermodynamically and kinetically there should be no reason to choose the silicon since restoring aromaticity is much faster and
thermodynamically downhill whereas attacking silicon would break an Si-O bond in favor of an Si-Cl bond, which is weaker. What are your guys'
thoughts? Should PhOTIPS survive FC conditions for acylation? Am I missing something?
[Edited on 14-5-2022 by gemar14]
[Edited on 14-5-2022 by gemar14]