Dimetallations of 2-substituted furans and thiophenes: approaches to the 2,3,5-trisubstituted heterocycles

The preparation and reactions of 3,5-dilithiated furan and thiophene derivatives bearing the 4,4-dimethyloxazolin-2-yl 2-substituent are reported. The 2-tert-butoxycarbonyl analogues cannot be prepared by direct dimetallation of the corresponding esters but sequential monometallation with in situ trapping by Me₃ SiCl ultimately affords the 3,5-disilylated products: the 3-metallation of the 5-silylated intermediate is accelerated by LiCl.     

A convenient synthesis of high-loaded palladium(II) ROMP polymers

Bis[1-(5-norbornen-2-yl)butan-1,3-dionato]palladium(II) was conveniently prepared from 5-acetoacetyl-2-norbornene and sodium tetrachloropalladate. The former could be subjected to ROMP to give a highly-loaded palladium(II) ROMP polymer with a palladium loading of 23% by weight.     

The Rearrangement of α-Acetylenic Alcohols to α, β-Unsaturated Carbonyl Compounds by Silylvanadate Catalysts

New catalytic systems have been found which effect the isomerization of α-acetylenic alcohols to the corresponding α, β-unsaturated carbonyl compounds with high efficiency. These are combinations of silylvanadates with silanols or silanediols.     

An experimental and theoretical study of crystals of calcium fluoride doped with alkali metal cations

Experimental measurements of thermal depolarization in crystals of CaF₂, grown from the melt containing LiF, NaF, KF, or RbF, reveal a common relaxation (designated M2) with an activation energy of 0.51 eV. In addition, the Li⁺- and K⁺-doped crystals exhibit a relaxation (M1) with an activation energy of 0.34eV. A similar relaxation has been found in CaF₂:Rb⁺ by J. Fontanella private communication) and in CaF₂:Na⁺ by R. D. Shelley and G. R. Miller (J. Solid State Chem., 1, 218, 1970). Theoretical calculations on M⁺-doped CaF₂ (where M = Li,Na,K,Rb) are in agreement with the hypothesis that the M2 relaxation is due to Na⁺ in all four systems studied and is associated with the jump of a nearest-neighbor (nn) anion vacancy (F_v^?) around the substitutional Na⁺ ion (Na_s⁺). The assignment of M1 is less certain, but it appears to be associated with similar Li_s⁺&.z.sbnd;F_v^? dipoles resulting from Li⁺ impurity present because of the lower volatility of LiF compared to that of KF and RbF. When LiF dissolves in CaF₂ the Li⁺ ion also forms quadrupoles consisting of a cation vacancy and two Li⁺ interstitials and the reorientation of these quadrupoles has also been studied theoretically.     

Alumina-titania oxides: Synthesis and characterization

Alumina-titania mixed oxides with nominal atomic ratios Al/Ti=25 and 2 have been synthesized by cohydrolysis of Al(OsecBu)₃ and Ti(OBu)₄. The oxides were amorphous at 500°C, showing only short range order. Ti was incorporated in alumina in a well dispersed way creating a true Al/Ti mixed oxide. The strength of surface acid sites and specific surface areas were increased at the higher Ti content. The TiO₂ anatase phase was avoided and rutile was formed directly at 900°C.