Toshimasa Suzuka

A new route for the construction of the AB-ring core of Taxol

Abstract A new method for the construction of the AB-ring core of Taxol was developed utilizing a new skeletal transformation protocol as a pivotal step. The acid-catalyzed rearrangement of the cyclopentenone–allene photoadduct gave a bridged seven-membered ketone, which was easily transformed, using the intramolecular Suzuki reaction and the oxidative cleavage of the vicinal diol, to the bicyclic diketone.

Reusable Polymer-Supported Terpyridine Copper Complex for [3+2] Huisgen Cycloaddition in Water

A polymer-supported terpyridine copper(I) complex was prepared and found to promote the Huisgen [3+2] cycloaddition reaction between azides and alkynes in water to give the corresponding triazoles with up to 87% isolated yield. This catalyst was recovered and reused several times without any loss in catalytic activity.

Reactivity of Aryl Halides for Reductive Dehalogenation in (Sea)water Using Polymer-Supported Terpyridine Palladium Catalyst

A polymer-supported terpyridine palladium complex was prepared. The complex was found to promote hydrodechlorination of aryl chlorides with potassium formate in seawater. Generally, reductive cleavage of aryl chlorides using transition metal catalysts is more difficult than that of aryl bromides and iodides (reactivity: I > Br > Cl); however, the results obtained did not follow the general trend. Therefore, we investigated the reaction inhibition agents and found a method to remove these inhibitors. The polymeric catalysts showed high catalytic activity and high reusability for transfer reduction in seawater.

Asymmetric Allylic Substitution in Water with a PolymericPd Catalyst

Significance: Asymmetric p-allylic substitution of meso-1,4-diacetoxycycloalkenes was performed with an amphiphilic PS-PEG resin-supported chiral phosphine-palladium complex. Thus, the reaction of cis-1,4-diacetoxycyclopentene (meso-1) with diethyl malonate, dibenzylamine and phenols in water gave the corresponding 1-acetoxy-4substituted cyclopentenes 2a–i with 90–99% ee in 43–64% yield. Cyclohexenyl ester (meso-4) also underwent etherification with phenol to give 5 in 37% yield (95% ee) and 11% of 6. Comment: The authors have reported earlier the preparation and utility of the polymeric chiral phosphine-palladium complex used here (J. Am. Chem. Soc. 2001, 123, 2919; Org. Lett. 2004, 6, 281; Org. Lett. 2005, 7, 291; Tetrahedron: Asymmetry 2006, 17, 161; J. Org. Chem. 2006, 71, 8644). The reaction pathway giving high enantiomeric excess of the monosubstituted products includes kinetic resolution steps forming disubstituted 3. N N O H