Tadashi Okuyama

Structure and reactivity of α,β-unsaturated ethers—IX : The cis-trans isomerization equilibria in the liquid phase

Abstract The relative stability of various pairs of cis- and trans-α,β-unsaturated ethers has been determined by geometrical isomerization equilibrium experiments. The isomerization was carried out in bulk in the presence of mercuric acetate at 20 to 50°. The trans isomers of alkenyl and styryl ethyl ethers generally are thermochemically more stable than the corresponding cis ethers by 0·4 to 1·7 kcal/mole. In the case of propenyl alkyl ethers, the methyl, ethyl, and isobutyl ethers are more stable in the trans form, whereas the reverse is true for both the isopropyl and t-butyl ethers. In all these cases, the entropy term favours the stability of the cis ethers. These facts are probably due to the rotational isomerism around the sp2 Cue5f8O bond. cis-β-Chlorovinyl and cis-β-ethoxyvinyl ethyl ethers were found to be more stable than the trans isomers.

Cyclic dithio-carbenium ion salts and their conversion to ketene dithioacetals

Abstract 1,2-Ethanedithiol and 1,3-propanedithiol were treated with perchloric acid in acetic anhydride to give 2-methyl-1,3-dithiolan-2-yl and 2-methyl-1,3-dithian-2-yl perchlorates, respectively, which were converted to ketene dithioacetals by deprotonation with tertiary amines.

Acid-catalyzed hydrolysis of alkyl vinyl and propenyl sulfides

Abstract The rates of acid-catalyzed hydrolysis of methyl, ethyl, isopropyl, and t-butyle vinyl sulfides have been measured in 10% aqueous acetonitrile. It was found that their reactivities decrease in this order. General acid catalysis was observed. The rate was smaller in a deuterium medium (kD2O/kH2O = 0.34). The deuterium exchange between sulfide and solvent was not detected during hydrolysis. Some propenyl sulfides have also been studied, their cis isomers being more reactive than the trans counterparts without geometrical isomerization involved. The reaction mechanism and the substituent effects on the reactivity have been discussed.

Chiral and flexible 2,4-pentanediol-tethered cyclopropanation of olefins with a carbenoid derived from a diazo ester to construct three stereogenic centers

Abstract 2,4-Pentanediol-tethered cyclopropanation of an olefin with an internal carbenoid generated from a diazo ester proceeded smoothly to give a chiral adduct having three stereogenic centers under full stereocontrol. The high stereoselectivity was not affected by the structure of the olefinic portion, studied so far with six substrates. Conversion of the product cyclopropane to other optically active compounds is also reported.

Hydroxy direction of zinc carbenoid addition to a remote olefin. Analysis and improvement of 2,4-pentanediol tethered Furukawa cyclopropanation

Abstract Zinc carbenoid addition to an olefin stereocontrolled by a chiral and remote intramolecular hydroxy group was studied in detail. Stereoselectivity as well as chemical yield of the Furukawa cyclopropanation was dramatically improved by modifications of the procedure of addition of the reagents. The structure of an active species to give the hydroxy-directed product is proposed.

Association and dissociation of (Z)-(β-bromoalkenyl)-(phenyl)iodonium bromide in chloroform solution: Detection of vinyl-λ3-iodane dimer in solution

Abstract Formation of the iodonium ion 1a as well as the dimer 3a is found in chloroform solution of ( Z )-(2-bromo-1-decenyl)(phenyl)iodonium bromide ( 2a ) by vapor pressure osmometry and 1 H NMR experiments, and the dissociation and association constants are determined. The dimer 3a is also detected by FAB-MS in the gas phase.

On the mechanism of nucleophilic substitution of allenyl(aryl)iodine(III): Formation of propargyl cation and competition with sigmatropic rearrangement

The ratios of nucleophilic substitution versus [3,3] sigmatropic rearrangement for the collapse of allenyl(aryl)-iodine(III), generated from the reaction of aryliodanes with propargylsilanes in the presence of BF3ue5f8Et2O in alcohols, were determined. A proposed mechanism involves generation of propargyl cations from the allenyliodine(III) via a unimolecular pathway.

Asymmetric synthesis by vapor phase pyrolysis

Abstract The first vapor phase asymmetric synthesis was successfully carried out by FVP of a 2,4-pentanediol (PD)-tethered substrate carrying cyclohexene and diazo ester moieties at high temperature up to 400°C. The intramolecular [2+2] cycloaddition of the ketene was strictly stereocontrolled by the entropy term.

Acid-catalyzed hydrolysis of ring-substituted phenyl vinyl sulfides

Abstract The acid-catalyzed hydrolysis of phenyl vinyl sulfide and its ring-substituted derivatives has kinetically been investigated in 40% aqueous dioxane and 90% aqueous tetrahydrofuran. The observed rate constants were satisfactorily correlated with the Hammett acidity function H0. The effect of substituents on the hydrolysis rates was found to conform to the Hammett σ- constants with ϱ = − 1.98 (40% dioxane, 30°). The ϱ value was compared with that found for the hydrolysis of phenyl vinyl ether in terms of the transmission efficiency of the S and O atoms.

Structure and reactivity of α,β-unsaturated ethers—XIV: Protonation of cis- and trans-1-ethoxybuta-1,3-dienes

Abstract The acid-catalysed hydrolysis and alcohol addition of cis- and trans-1-ethoxybuta-1,3-dienes have been investigated. It was found by product analyses with deuterium incorporation experiments that in both the reactions the cis isomer protonates at the 2-position as well as at the 4-position while the trans isomer protonates exclusively at the 4-position. The kinetic experiments showed that the trans isomer is much more reactive than the cis isomer. The possible origin of the observations is discussed.