A Base‐Free Neutral Phase‐Transfer Reaction System

Although phase‐transfer reactions catalyzed by using quaternary ammonium salts are generally believed to require base additives, we discovered that, even without any base additives, conjugate additions of 3‐substituted oxindoles to nitroolefins proceeded smoothly in the presence of lipophilic quaternary ammonium bromide under water–organic biphasic conditions. The mechanism of this novel base‐free neutral phase‐transfer reaction system is investigated and the assumed catalytic cycle is presented together with interesting effects of water and lipophilicity of the phase‐transfer catalyst. The base‐free neutral phase‐transfer reaction system can be applied to highly enantioselective conjugate addition and aldol reactions under the influence of chiral bifunctional ammonium bromides as key catalysts. The structure of the chiral ammonium enolate intermediate is discussed based on the single‐crystal X‐ray structures of relevant ammonium salts and the importance of bifunctional design of catalyst is clearly explained in the model of intermediate.     

Stereoselective synthesis of the right-hand segment of tubiferal A

Tubiferal A, a triterpenoid isolated from myxomycete Tubifera dimorphotheca, exhibits a reversal effect of vincristine (VCR) resistance against VCR-resistant KB cell lines. The compound possesses a complex structure involving the 6-7-6-5 polycyclic carbon framework with various functional groups. The stereoselective synthesis of the right-hand segment of tubiferal A was achieved on the basis of the cyclopentene annulation method and the semi-pinacol rearrangement reaction of an epoxy alcohol for constructing the trans-fused 6-5 bicyclic skeleton possessing two quaternary carbon atoms at the angular positions.     

Asymmetric phase-transfer reactions under base-free neutral conditions

Although quaternary onium salt-catalyzed phase-transfer reactions are generally believed to require base additives, we discovered even without any base additives conjugate additions of 3-substituted oxindoles proceeded smoothly in the presence of lipophilic quaternary onium bromide under water-organic biphasic conditions. The mechanism of this novel base-free neutral phase-transfer reaction system was investigated, and the assumed catalytic cycle was presented together with interesting effects of water and lipophilicity of the phase-transfer catalyst. The base-free neutral phase-transfer reaction system could be applied to highly enantioselective conjugate additions, aldol reaction, sulfenylation, and chlorination under the influence of chiral bifunctional onium bromides as key catalysts.     

Electrochemical performance of nanocomposite LiMnPO4/C cathode materials for lithium batteries

A LiMnPO₄/C composite cathode was prepared by a combination of spray pyrolysis and wet ball milling. The cathode showed stable performance at various cutoff voltages up to 4.9 V. The cutoff voltage increase up to 4.9 V allowed the achievement of a high discharge capacity in galvanostatic charge–discharge tests. The discharge capacities of 153 mAh g^?1 at 0.05 C and 149 mAh g^?1 at 0.1 C were achieved at room temperature; the trickle-mode discharge capacities at room temperature were 132, 120 and 91 mAh g^?1 at 0.1, 1 and 5 C discharge rates, respectively. The cell exhibited a good rate capability in the galvanostatic cycling up to 5 C discharge rates at both ambient temperature and 50 °C.     

Absolute configurations of endoperoxides determined by vibrational circular dichroism (VCD)

Diastereomeric mixture on the peroxide portion of an endoperoxide acetylmajapolene A (1) was efficiently separated by HPLC on a chiral column, submitting to vibrational circular dichroism (VCD) investigation. The ab initio theoretical VCD and IR calculations of 1a and 1b were performed by density functional theory (DFT) using the B3PW91/6-31G(d,p) level of theory. Focusing on an isolated characteristic peroxide vibrational band, absolute configurations of 1a and 1b were unambiguously determined as (1R,4R,7S,10S) and (1S,4S,7S,10S), respectively. This is the first VCD application to endoperoxides which exist abundantly in nature.     

Toward Palau′amine: Hg(OTf)2‐Catalyzed Synthesis of the Cyclopentane Core

Catalytic cyclization : The Hg(OTf)₂‐catalyzed N‐selective cyclization of amide carbonyl moieties for the construction of a quaternary carbon center was developed. The Hg(OTf)₂‐catalyzed cyclization of cyclopentylidene alcohol with acylhydrazide afforded the desired cyclopenta[c]pyridazinone in good yield. The subsequent eight steps gave the functionalized cyclopentane with the correct stereochemistry that corresponds to the E ring of palau′amine (see scheme).

     

Synthesis and Reactions of 1-Phenylbenzo[b]thiophenium Salts

1-Phenylbenzo[b]thiophenium salts are prepared and reacted under thermal and photochemical conditions. The chemical behaviors are discussed.