The catalytic enantioselective synthesis of tetrahydrofurans, which are found in the structures of many biologically active natural products, via a transition-metal-catalyzed hydrogen atom transfer (TM-HAT) and radical-polar crossover (RPC) mechanism is described herein. Hydroalkoxylation of nonconjugated alkenes proceeded efficiently with excellent enantioselectivity (up to 94% ee) using a suitable chiral cobalt catalyst, N-fluoro-2,4,6-collidinium tetrafluoroborate, and diethylsilane. Surprisingly, the absolute configuration of the product was highly dependent on the steric hindrance of the silane. Slow addition of the silane, the dioxygen effect on the solvent, thermal dependence, and DFT calculation results supported the unprecedented scenario of two competing selective mechanisms. For the less-hindered diethylsilane, a high concentration of diffused carbon-centered radicals invoked diastereoenrichment of an alkylcobalt(III) intermediate by a radical chain reaction, which eventually determined the absolute configuration of the product. On the other hand, a more hindered silane resulted in less opportunity for a radical chain reaction, instead facilitating enantioselective kinetic resolution during the late-stage nucleophilic displacement of the alkylcobalt(IV) intermediate.

Catalytic enantioselective synthesis of tetrahydrofurans, which are found in the structures of many biologically active natural products, via a transition-metal catalyzed-hydrogen atom transfer (TM-HAT) and radical-polar crossover (RPC) mechanism is described herein. Hydroalkoxylation of non-conjugated alkenes proceeded efficiently with excellent enantioselectivity (up to 94% ee) using a suitable chiral cobalt catalyst, <i>N</i>-fluoro-2,4,6-collidinium tetrafluoroborate, and diethylsilane. Surprisingly, absolute configuration of the product was highly dependent on the steric hindrance of the silane. Slow addition of the silane, the dioxygen effect in the solvent, thermal dependency, and DFT calculation results supported the unprecedented scenario of two competing selective mechanisms. For the less-hindered diethylsilane, a high concentration of diffused carbon-centered radicals invoked diastereoenrichment of an alkylcobalt(III) intermediate by a radical chain reaction, which eventually determined the absolute configuration of the product. On the other hand, a more hindered silane resulted in less opportunity for radical chain reaction, instead facilitating enantioselective kinetic resolution during the late-stage nucleophilic displacement of the alkylcobalt(IV) intermediate.

States of water molecules confined in a nanospace designed by montmorillonite (negatively charged silicate layer) and charge compensating benzyl­ammonium were investigated. Caffeine was used as a probe because of its compatibility for the fine structure of the interlayer water. Powder synchrotron radiation X-ray diffraction (SXRD) and adsorption isotherms of the water vapor revealed a metastable structure of bimolecular water layers (2WLs) in the interlayer space. Water molecules readily penetrated to expand the interlayer space to 0.56 nm. The interlayer space did not increase further even in the presence of excess water. According to the isosteric heat of water, the expansion was limited because of moderate hydration as forming 2WLs. Caffeine molecules replaced a part of the water molecules in the 2WLs to expand the interlayer space to 0.65 nm. Time-resolved SXRD with an accumulation time of 500 ms revealed that the interlayer expansion reached a steady state within a few minutes. The caffeine intercalation proceeded, involving a change in the molecular orientation that increased the contact area of the caffeine molecules. The interlayer expansion was limited in all the solvents examined (mixtures of water with methanol, ethanol, acetone, and tetrahydrofuran), while the packing density of the incorporated caffeine was maximized in the absence of an organic solvent. The water molecules confined in the interlayer space acted as an actuator to accommodate a large quantity of amphiphilic molecules by adapting the nanostructure, which was achieved by releasing the confined water molecules.

The catalytic enantioselective synthesis of tetrahydrofurans, found in the structures of many biologically active natural products, via a transition-metal-catalyzed hydrogen atom transfer (TM-HAT) and radical-polar crossover (RPC) mechanism is described. Hydroalkoxylation of non-conjugated alkenes proceeded efficiently with excellent enantioselectivity (up to 97:3 er) using a suitable chiral cobalt catalyst, <i>N</i>-fluoro-2,4,6-trimethylpyridinium tetrafluoroborate, and a diethylsilane. Surprisingly, absolute configuration of the product was highly dependent on the bulkiness of the silane. Mechanistic studies suggested a HAT mechanism and multiple enantiodetermining steps via an organocobalt(III) intermediate. DFT calculations suggested the presence of a cationic organocobalt intermediate, and that a critical factor of the enantioselectivity is the thermodynamic stability of the organocobalt(III) intermediate.

A correction method was developed for estimation of daily dietary iodine intake. The iodine intake level for preschoolers was comparable to levels for adult population.