Stable carbocations. CLXXXIII. Haloacetylium ions

Preparation of α,β-Unsaturated Ketones Bearing a Trifluoromethyl Group and Their Application in Organic Synthesis

“…Attempts to improve their activity with Lewis acids (as in the case of aromatic hydrocarbons' trifluoroacylation [32][33][34]) lead to cationic polymerization of the unsaturated substrates. Perfluorinated acylium salts which can be used for the perfluoracylation of unsaturated hydrocarbons are unstable and decompose readily with decarbonylation (Eq.1) [35,36].…”

Carbocationic rearrangement of pivaloyl cation and protonated pivalaldehyde in superacid medium: A novel solution equivalent of the McLafferty rearrangement

“…In the superelectrophilic formylation of isobutane, the formyl cation in HF:BF 3 (1:1) can undergo further protosolvation (HCO ϩ . .…”

“…Activation of acyl ions by Lewis acids has been studied extensively by Vol'pin et al [21] and they found that in the low temperature isomerization of saturated hydrocarbons, a 1:1 CH 3 COX-AlX 3 Friedel-Crafts complex was found to be inactive where as CH 3 COX-2AlX 3 (1:2) complex was found to be highly reactive due to the superelectrophilic character of the acetylium ion by further O-complexation with a second molecule of AlCl 3 . Theoretical calculations at the HF/6-31G* level have shown that O-protonation of the acetyl ion leads to a stable but highly electron deficient, superelectrophilic gitonic dication, CH 3 ϪC ϩ ¢O ϩ ϪH (9b) which corresponds to a global minimum on the potential energy surface [22].…”

“…Also the acylium salts in superacid media are found to be excellent acylating agents for deactivated aromatics. However, Olah et al have shown that such reactions do not take place with acylium salts themselves in the absence of superacids in aprotic solvents such as SO 2 , SO 2 ClF, AsF 3 , or CH 2 Cl 2 [3].…”

2-Chloro-3-(dimethylamino)prop-2-enoyl Fluoride, a Stable Acyl Fluoride

“…The size of this coupling constant shows that the F-atom is directly bound to a CO C-atom (cf. the CO signal of AcF [3]: 162.7 ppm, 1 J 356 Hz, or of PhCOF [4]: 158.0 ppm, 1 J 343.5 Hz). Likewise, the large coupling constant of 77 Hz ( 2 J(C,F)) of the signal at 80.4 ppm requires the corresponding C-atom to be in b-position to the F-atom [3] [4].…”