Haruhiko Fukaya

The gas‐phase acidities of very strong neutral Brønsted acids are estimated based on Gaussian theory and two‐layer ONIOM calculations. Although the calculated gas‐phase acidities using Gaussian theory are in excellent agreement with the experimental values, these high‐level calculations are limited to small molecules because of their high computational cost. ONIOM calculation with the smallest model system, where only the acid center is placed in the high layer, gives relatively poor results. In contrast, ONIOM calculation with a model system expanded to neighbor atoms or the next neighbor atoms of the acid center gives estimates of gas‐phase acidities with practically useful accuracy.

Efavirenz is manufactured worldwide, and its asymmetric synthesis requires a complex organometallic approach, while an organocatalytic approach is far less efficient. The first highly enantioselective approach is disclosed for the synthesis of Efavirenz under nonmetal organocatalysis with up to 93% ee for the Merck intermediate and 91% ee for the Lonsa intermediate using novel alkynyl cinchona catalysts.

Hexafluoropropene trimers were reacted with C₆F₅Si(CH₃)₃ to provide not only pentafluorophenyl but also perfluorophenylene derivatives [F(C₆F₄)_nC₉F₁₇; n=2–9] by successive pentafluorophenylation of perfluoroaryl rings. Their structures, including rotational isomers, were determined by MS, ¹⁹F and ¹³C–{¹⁹F} NMR spectroscopy, and/or X‐ray crystallography, and were further confirmed by B3LYP‐GIAO calculation of NMR shieldings. Formation of a pair of gear‐meshed rotamers with clockwise and counterclockwise conformations was identified by NMR measurements for the structures having geminal (CF₃)₂CF groups at the C=C bond. That the predominantly formed counterclockwise rotamer was gradually converted to the clockwise rotamer over 50 days at room temperature through a synchronized movement of gears was also confirmed by NMR measurements. A comparison between the X‐ray structure and B3LYP calculations showed some structural differences that arise from the crystal packing.

Gas-phase acidities of polyfluorinated hydrocarbons have been determined by measuring proton-transfer equilibria and by computing the free energies of deprotonated carbanions and the corresponding neutrals. An excellent linear relationship between acidities and the accumulated inductive effects of fluorine atoms contained in a molecule was observed for the perfluoroalkyl-substituted neopentanes, (Rf1)(Rf2)(Rf3)CCH3, and polyfluorinated bridgehead carbon acids where the contribution of negative hyperconjugation of the Cβ–F bond to the stability of the conjugate anions is absent or negligibly small. On the basis of this relationship, the extent of β-fluorine negative hyperconjugation involved in acidities of polyfluorinated hydrocarbons could be evaluated quantitatively. The negative hyperconjugation was found to be negligibly small in the stable tertiary polyfluorinated carbanions while in the less stable primary and secondary carbanions the contribution of this effect is present certainly, indicating that the negative fluorine hyperconjugation is complementary to the stabilization by the accumulated inductive effect of fluorine atoms. The extent of negative hyperconjugation was found to increase in order of CF3CH2− < C2F5CH2− ≈ C3F7CH2− < i-C3F7CH2−, being qualitatively consistent with the elongation of the Cβ–F bond by deprotonation. The effect of α-fluorine on acidity was found to change complicatedly with the carbanion, e.g., the α-fluorine substitution in CF3CH3 strengthens acidity, no effect in (CF3)2CH2, and strengthens again acidity in (i-C3F7)2CH2. Such varying effect of α-fluorine in the polyfluorinated hydrocarbons would be caused by a subtle balance of effective electronegativity of an anionic center carbon, a varying p–p lone pair repulsion depending on the net negative charge at the formal charge center carbon, and the change in ability of β-F negative hyperconjugation caused by α-F substitution.

The effects of doped low‐valence cations on the properties of the SnP₂O₇ proton conductor at ambient temperature are investigated from changes in solid‐state NMR spectra and nuclear magnetic relaxation times. Although the T₁H values increased with decreasing acidity as a result of cation exchange, the ¹H chemical shifts moved to lower field in Al‐ and In‐doped materials compared with undoped ones. Furthermore, the shifts changed to higher field in Mg‐doped materials, suggesting the existence of different protonic species in those materials. The bulk phosphate chemical shifts in the ³¹P dipolar‐decoupling MAS NMR spectra were very similar, regardless of the nature and amount of the doping species. On the other hand, by ¹H/³¹P cross‐polarization MAS NMR, P₂O₇ signals interacting with an interstitial proton [Q¹(proton)] were observed in all the undoped and doped SnP₂O₇, while acidic P–OH‐type phosphate signals [Q¹(acid)] were additionally observed in the Mg‐doped conductor. The different affinity of the proton with the dopants and phosphates caused lower conductivity and larger activation energy in the Mg‐doped materials, compared with those in the In‐ and Al‐doped materials. Copyright © 2014 John Wiley & Sons, Ltd.