Solvent effect on distribution ratio of Pd(II) in supercritical carbon dioxide extraction and solvent extraction using 2-methyl-8-quinolinol

The distribution ratio (D_M) of Pd(II) by the extraction with 2-methyl-8-quinolinol (HMQ) was determined using the supercritical carbon dioxide medium (SF-CO₂) and organic solvent media such as perfluoro-methylcyclohexane, heptane, cyclohexane, carbon tetrachloride and benzene. From experimental results of the slopes of log D_M versus pH plot and log D_M versus HMQ concentration plot, the extracted species both in the SF-CO₂ extraction (SFE) and the solvent extraction (SE) were determined to be Pd(MQ)₂. The distribution constant of HMQ (K_D,HMQ) in the SFE and SE systems were determined from the dependence of the distribution ratio of HMQ (D_HMQ) on the pH. A linear relationship was observed between log K_D,HMQ and the solubility parameter (δ) of the extraction medium based on the regular solution theory in both the SFE using SF-CO₂ at the pressure of 8.5–40 MPa and the SE systems. The difference in the slope of the log K_D,HMQ versus δ plot between the SFE and the SE systems is attributable to the extent of the specific interaction of the solute HMQ with the solvent molecules, i.e. CO₂ molecules and the organic solvent molecules. The D_M versus δ plot obtained under a given extraction condition using SF-CO₂ (11–40 MPa) and organic solvents showed clear linearity. The D_M obtained using SF-CO₂ at relatively low pressure range from 8.5 to 11 MPa was independent of the pressure and the δ of SF-CO₂, which coincides with the experimental fact that the solubility of Pd(MQ)₂ in the SF-CO₂ at 8.5–11 MPa was practically constant.     

A facile synthetic method of α-quaternary-β,γ-unsaturated aldehydes via the stereoselective 1,4-elimination and α-regioselective Ferrier reaction

The 1,4-elimination reaction of 2-substituted-(2Z)-4-methoxy-O-alkenyl acetals with n-butyllithium is shown to afford the 2-substituted-(1Z,3E)-O-1,3-dienyl acetals in high stereoselectivities. The Ferrier reaction of the O-1,3-dienyl acetals thus obtained provides the corresponding α-quaternary-β,γ-unsaturated aldehydes in excellent yields with high α-regioselectivities.     

Stereospecific deoxydichlorocyclopropanation of expoxides by dichlorocarbene generated in an emulsifying system

The reaction of epoxides with dichlorocarbene generated in an emulsifying system was investigated. The products were the corresponding dichlorocyclopropane derivatives. The reaction of cis- and trans-β-methylstyrene oxides showed the reaction was completely stereospecific. Styrene oxide gave the corresponding dichlorocyclopropane and styrene, where the concentration of the latter was kept in the nearly stationary state during the reaction. Further the competitive reaction of α- and β-methylstyrene oxide showed that introduction of an additional Me group at the α-position accelerated the reaction only 12 times. From these observations the reaction was concluded to involve the two step process, namely, the deoxygenation process and dichlorocyclopropanation process, both of which were stereospecific and practically concerted.     

Palladium-catalyzed coupling reaction of propargylic oxiranes with arylboronic acids in aqueous media

A novel type of coupling reaction has been developed by the palladium-catalyzed reaction of propargylic oxiranes with arylboronic acids, in which anti-substituted 4-aryl-2,3-allenols were produced in a highly diastereoselective manner. A chiral-substituted allene has been synthesized from the reaction of a chiral propargylic oxirane without loss of the chirality.     

Catalytic asymmetric arylative cyclization of alkynals: phosphine-free rhodium/diene complexes as efficient catalysts

Catalytic arylative cyclization of alkynals has been developed by the use of phosphine-free rhodium/diene complexes as catalysts. An asymmetric variant of this process has been successfully realized by employing a C2-symmetric chiral bicyclo[2.2.2]octadiene ligand. The rhodium/diene catalyst system is also effective for arylative cyclization of other substrates such as alkynones and enynes, achieving multiple carbon-carbon bond formations in a single step.     

Generation of sec-thioamide dianions and their regioselective reaction with electrophiles.

The enolates of sec-thioamides $\text{8}$, which are generated by three different methods (scheme II and equation 1), are alkylated selectively at the α-carbon to the thiocarbonyl group. The unusual β′-lithiation to provide an intermediate $\text{11}$ is observed for N-methyl-α, β-dimetylthioacrylamide and N-methyl-thiocyclohexenecarboxamide.