Jun'ichi Uenishi

A general and convenient synthetic method of geometrically pure (Z)-1-bromo-1-alkenes

Abstract Palladium catalyzed hydrogenolysis of 1,1-dibromo-1-alkenes by tributyltin hydride proceeds smoothly to give ( Z )-1-bromo-1-alkenes with excellent stereoselectivity in good yields. Dibromomethylenation of aldehydes by a combination of CBr 4 and Ph 3 P in methylene chloride and the successive hydrogenolysis affords ( Z )-1-bromo-1-alkenes in one-pot.

Stereocontrolled Synthesis of (11Z)-Retinal and Its Analogues

Suzuki coupling of stereochemically pure (Z)-bromotetraene 1-which is extremely unstable but can be kept in frozen benzene in the presence of a small amount of PPh3 at &sminus 01;20°C-and (Z)-alkenylboronic acid 2 provides the stereocontrolled synthesis of (11Z)-retinal 3. The 11Z configuration, which is introduced by selective catalytic debromination of the corresponding dibromo precursor of 1, is retained in this step. TBDMS = tBuMe2 Si.

Intramolecular Sm2+ and Sm3+ promoted reaction of γ-oxy-δ-ketoaldehyde; stereocontrolled formation of pinacol and lactone

Abstract Samarium promoted intramolecular pinacol coupling and Tishchenko oxidoreduction of γ-oxy-δ-ketoaldehyde proceeded stereospecifically. Newly forming hydroxy group is oriented anti to γ-silyoxy group in both reactions.

Ipso substitution of 2-alkylsulfinylpyridine by 2-pyridyllithium; a new preparation of oligopyridine and their bromomethyl derivatives

Abstract Unsymmetrical and symmetrical 2,2′-bipyridines 5 and 6 have been prepared. The methods applied are new and offer efficient syntheses of higher oligopyridines and their bromomethyl derivatives.

Asymmetric synthesis of D- and L-2-deoxy-4-thioriboscs

Abstract Both D- and L-enantiomers of 2-deoxy-4-thioribose derivatives 12 and 17 were prepared stereospecifically in 12 steps from 1,3-propanediol. The key intermediary 2,3-epoxy alcohols, 8 and 15 were obtained with high enantiomeric excess by the Sharpless asymmetric epoxidation using (+)-L-diethyl tartrate and (−)-D-diethyl lartrate.

Synthetic studies of halichondrin B, an antitumor polyether macrolide isolated from a marine sponge. 8. Synthesis of the lactone part (C1C36) via horner-emmons coupling between C1C15 and C16C36 fragments and Yamaguchi lactonization

Abstract The lactone part ( 2 ) of halichondrin B ( 1 ) was synthesized by Yamaguchi macrolactonization of the seco-acid ( 3 ), which was synthesized via coupling of C1C15( 4 ) with C16C36 ( 5 ), prepared through stereoselective construction of the E ring starting from C16C26 ( 7 ) and C27C36 ( 8 ).

An optical resolution of pyridyl and bipyridylethanols and a facile preparation of optically pure oligopyridines

Abstract A kinetic resolution of racemic pyridyl and bipyridylethanols was performed by Candida antarctica lipase with vinyl acetate in diisopropyl ether, in which (R)-alcohol was acetylated stereoselectively, and both the acetate 2 and the remaining (S)-alcohol 1 were obtained with high enantiomeric excesses. (S0-Oligopyridylethanols, 7 and 8 were prepared by a coupling reaction of (S)-1b and (S)-1e with ethyl bipyridyl sulfoxide.

Tridentate pyridine podand ionophores exhibiting perfect Ag+ ion selectivity

Abstract A new type of podand ionophores was prepared, in which three pyridine moieties were appropriately arranged for tridentate Ag + complexation. They well discriminated Ag + ion from Pb 2+ , Cu 2+ , Co 2+ , Zn 2+ and Ni 2+ ions and mediated selective and efficient transport of Ag + ion.

An extremely mild desulfurization of thiiranes; an efficient transformation from geraniol to (+)- and (−)-linalool

Abstract Thiirane was transformed to alkene very efficiently at −78°C by triethylborane initiated radical reaction with tributyltin hydride. Enantiomerically pure (+)- and (−)-linalools were derived from geraniol in four steps including the alkene formation reaction.

Stereocontrolled synthesis of dehydrodendrolasin: Unstable polyene furanosesquiterpenoids

Abstract Marine furanosesquiterpenoids, (2E,4E,6E)- and (2Z,4E,6E)-dehydrodendrolasin (2) and (3), were synthesized in a geometrically controlled fashion. For the synthesis of 2, stereospecific addition of methyl(tributylstannyl)magnesium to E-enyne was employed effectively to afford (2E,4E)-3-(5-iodo-4-methyl-2,4-pentadienyl)furan (15). For the synthesis of 3, the key geometrical control for Z-enyne intermediate (7) was performed by a Pd catalyzed stereospecific hydrogenolysis of 3-(3-furyl)-1,1-dibromopropene (16) and successive Sonogashira coupling with trimethylsilylacetylene to give (Z)-3-(5-trimethylsilyl-2-penten-4-ynyl)furan (18) in one pot.