Relay Propagation of Crowding: The Trifluoromethyl Group as Both an Emitter and Transmitter of Steric Pressure

Abstract

Whereas lithium 2,2,6,6-tetramethylpiperidide (LITMP) abstracts a proton exclusively from the 4-position of 3-bromobenzotrifluoride, the same base attacks selectively the 2-position when employed in the presence of N,N,NЈ,NЈЈ,NЈЈ-pentamethyldiethylenetriamine and potassium tert-butoxide ("Faigl mix"). 1-Bromo-3,5-bis(trifluoromethyl)benzene also undergoes metalation at the 2-position but [2-bromo-4-(trifluoromethyl)phenyl]silane does not react at all, evidently locked up by a C-SiR 3 /C-Br buttressing effect. 2-Bromo-4-(trifluoromethyl)pyridine, aza-analogous to the parent model arene 3-bromobenzotrifluoride, and both the benzo-azaanalogous 2-bromo-4-(trifluoromethyl)quinoline and its regioinverted isomer 4-bromo-2-(trifluoromethyl)quinoline are again readily deprotonated at the Br-and CF 3 -flanked posi-

Trifluoromethyl‐Substituted Phenylsilanes: The Regiochemical Course of Their Metalation Dictated by Buttressing Effects

“…As previously reported, [1][2][3] chlorine and bromine atoms are potent transmitters of the steric pressure emanating from an adjacent trialkylsilyl substituent. As we expected trifluoromethyl groups to behave similarly, we have selected three archetypical model compounds belonging to the benzotrifluoride family to verify this hypothesis.…”

Substituent effects on the relative rates and free energies of ortho-lithiation reactions: families of fluorobenzenes as the substrates

“…In some cases (e.g. with X = SiMe 3 ), buttressing effects [34][35][36][37][38][39][40][41] (steric effects exerted by the X group through the fluoro group) 42 may compromise the reactivity of the 1,2-isomers 2. More importantly, the acidifying effect of substituents at meta positions is no longer the same as at ortho positions.…”

Fluorine‐Flanked Congested Sites: Minimal, Though Perceptible Buttressing Effects on the Proton Mobility of Arenes

“…Hypotheses about its origin, nature and implications are still tentative. [15,16] To gain more insight, one first has to explore the scope of the phenomenon.…”