Katsuji Ito

Highly enantioselective Baeyer–Villiger oxidation using Zr(salen) complex as catalyst

(R,R)-Zr(salen) complex was found to serve as an efficient catalyst for asymmetric Baeyer–Villiger oxidation of pro-chiral and racemic ketones using urea·hydrogen peroxide as the terminal oxidant: for example, high enantioselectivity of 87% ee was achieved in the Baeyer–Villiger reaction of 3-phenylcyclobutanone.

A new methodology for the stereoselective synthesis of 4-substituted butenolides: Asymmetric Michael addition reaction of 2-(trimethylsilyloxy)furans to oxazolidinone enoates

Abstract Chiral Lewis acid promoted Michael addition of 2-(trimethylsilyloxy)furans to oxazolidinone enoates ( 2 ) in the presence of hexafluoroisopropanol proceeded stereoselectively to give 4-substituted butenolides in good yields. A 1:1 complex prepared in situ from Sc(OTf) 3 and 3,3′-bis(diethylaminomethyl)-1,1′-bi-2-naphthol 5b showed excellent anti -selectivity and moderate enantioselectivity, while Cu(OTf) 2 -bis(oxazoline) complex exhibited excellent enantioselectivity and moderate to good anti -selectivity.

Catalytic asymmetric cyclopropanation using copper complex of optically active bipyridine as a catalyst

Optically active 8,8′-di(trimethylsilyl)-5,5′,6,6′,7,7′,8,8′-octahydro-2,2′-biquinoline (7) was found to be an effective catalyst for enantioselective cyclopropanation of olefins. For example, the reaction of styrene and t-butyl diazoacetate in the presence of 7 proceeded with high enantioselectivity of 92% ee, to give t-butyl trans-2-phenylcyclopropanecarboxylate. On the other hand, the reaction of trans-β-methylstyrene gave the cis-isomer of >99% ee as a major product.

Chiral bipyrindine and biquinoline ligands: Their asymmetric synthesis and application to the synthesis of trans-whisky lactone

Chiral bipyrindine and biquinoline which have been reported to be efficient ligands for the construction of chiral copper catalysts, were synthesized enantioselectively by using Mn-salen catalyzed asymmetric epoxidation as a key step. Enantioselective synthesis of trans-whisky lactone was then achieved by way of enantiospecific ring expansion reaction of oxetane with a chiral copper catalyst bearing the bipyrindine ligand as a chiral source.

A SHORT-STEP SYNTHESIS OF TRANS-WHISKY LACTONE BY AN ASYMMETRIC MICHAEL REACTION

Abstract trans -Whisky lactone 6 was synthesized enantioselectively in only six steps from readily available 2-trimethylsilyloxyfurans and 3-crotonoyl-1,3-oxazolidin-2-one using an asymmetric Michael reaction as the key step.

New Asymmetric Catalysis by (Salen)cobalt(III) Complexes (Salen=[Bis(salicylidene)ethylenediaminato]={{2,2′‐[ethane‐1,2‐diyl]bis[(nitrilo‐κN)methylidyne]bis[phenolato‐κO]}(2−)}) of cis‐β‐Structure: Enantioselective Baeyer‐Villiger Oxidation of Prochiral Cyclobutanones

A series of chiral (salen)cobalt(III) complexes (salen=[bis(salicylidene)ethylenediaminato]={{2,2′-[(ethane-1,2-diyl)bis[(nitrilo-κN)methylidyne]bis[phenolato-κO]}(2−)}) of cis-β structure were prepared and used for the enantioselective Baeyer-Villiger oxidation of prochiral cyclobutanones with hydrogen peroxide as terminal oxidant. Both cationic (salen)cobalt(III) and neutral iodo(salen)cobalt(III) complexes 3–5 and 7–12, respectively, all having a chiral binaphthalenediamine unit, were found to be effective catalysts for the enantioselective Baeyer-Villiger oxidation (Tables 1, 3, and 4). In particular, complex 8 bearing electron-withdrawing F-atoms showed a good level of enantioselectivity (75–79% ee) in the reactions of 3-arylcyclobutanones (Scheme 4). On the other hand, complex 12 bearing tBu groups at C(3) and C(3′) and electron-withdrawing NO2 groups at C(5) and C(5′) (trivial numbering) exhibited a high enantioselectivity of 98% ee in the reaction of a tricyclic cyclobutanone (Table 4).