Kazuhiko Takahashi

New synthetic methods for α,β -unsaturated ketones, aldehydes, esters and lactones by the palladium-catalyzed reactions of silyl enol ethers, ketene silyl acetals, and enol acetates with allyl carbonates

Abstract Silyl enol ethers and ketene silyl acetals derived from ketones, aldehydes, esters and lactones are converted into α,β-unsaturated ketones, aldehydes, esters and lactones by treatment with allyl carbonates in high yields using the palladium—bis(diphenylphosphino)ethane (dppe) complex as catalyst. Phosphine-free palladium catalyst instead of the palladium—phosphine complex gives a higher selectivity for the preparation of cyclopentenone, cyclooctenone, dienones, α,β-unsaturated esters and lactones. As a solvent, the use of nitriles such as acetonitrile is essential. In other solvents, allylation takes place. Enol acetates derived from ketones are converted into α,β-unsaturated ketones by reaction with allyl carbonate in acetonitrile using the palladium complex and tributyltin methoxide as bimetallic catalysts.

Palladium-catalyzed preparation of α-allyl esters and α,β-unsaturated esters from saturated esters via their silyl acetals

Abstract Reaction of ketene silyl acetals with allylic carbonates in the presence of palladium-phosphine catalyst in dioxane gives α-allyl esters in high yields. When the reaction is carried out with phosphine-free palladium catalyst in nitriles, α,β-unsaturated esters are obtained in good yields.

Diastereocontrol via the phenol- and palladium(II)-catalyzed Claisen rearrangement with cyclic enol ethers

Abstract Taking the judicious choice of either 2,6-dimethylphenol or PdCl 2 (RCN) 2 as the catalyst, the Claisen rearrangements with the enol ethers of cyclic ketones are shown to proceed with a high level of either anti or syn diastereoselection, respectively.

Retroposition of the AFC Family of SINEs (Short Interspersed Repetitive Elements) Before and During the Adaptive Radiation of Cichlid Fishes in Lake Malawi and Related Inferences About Phylogeny

Abstract. Lake Malawi is home to more than 450 species of endemic cichlids, which provide a spectacular example of adaptive radiation. To clarify the phylogenetic relationships among these fish, we examined the presence and absence of SINEs (short interspersed repetitive elements) at orthologous loci. We identified six loci at which a SINE sequence had apparently been specifically inserted by retroposition in the common ancestor of all the investigated species of endemic cichlids in Lake Malawi. At another locus, unique sharing of a SINE sequence was evident among all the investigated species of endemic non-Mbuna cichlids with the exception of Rhamphochromis sp. The relationships were in good agreement with those deduced in previous studies with various different markers, demonstrating that the SINE method is useful for the elucidation of phylogenetic relationships among cichlids in Lake Malawi. We also characterized a locus that exhibited transspecies polymorphism with respect to the presence or absence of the SINE sequence among non-Mbuna species. This result suggests that incomplete lineage sorting and/or interspecific hybridization might have occurred or be occurring among the species in this group, which might potentially cause misinterpretation of phylogenetic data, in particular when a single-locus marker, such as a sequence in the mitochondrial DNA, is used for analysis.

Intramolecular ene approach to stereocontrol over three contiguous chiral centers

Abstract An intramolecular ene approach to stereocontrol over contiguous chiral centers is described, where three centers can be created with remarkably high level of both diastereofacial selectivity and diastereoselectivity by virtue of the preexisting chiral center in the ene component.

Sequential Claisen-ene approach to carbocyclization: a new entry to a steroid C/D ring synthon

Abstract A new and facile entry to a steroid C/D ring synthon is described which relies on the sequential combination of the Claisen rearrangement with the intramolecular ene reaction involving an acetylenic bond with methoxycarbonyl group as the enophile.