Kinetically controlled optical resolution of racemic norbornene aldehyde derivatives

Development of New Innovative Synthetic Organic Chemistry Using Lone Pairs of Oxygen Atoms

Oxygen atoms have a lone pair of electrons, so they have high chelation ability, high nucleophilic ability, stabilizing ability of adjacent cations, and take a chelate or oxocarbenium ion structure with Lewis acids and metals. I took advantage of these properties to develop three new reactions, 1) asymmetric synthesis of chiral quaternary carbon centers, 2) asymmetric synthesis using acetal functions, and 3) organic chemistry using acetal-type reactive salt chemical species, and applied them to biologically active natural products synthesis. New reactions described here are all innovative and useful for natural products synthesis. In particular, the first asymmetric synthesis of fredericamycin A, and concise asymmetric synthesis of anthracycline antibiotics, scyphostatin, (+)-Sch 642305, (-)-stenine, clavolonine, (+)-rubrenolide, (+)-rubrynolide, (+)-centrolobine, and decytospolide A and B, etc., are noteworthy. Furthermore, since reactions using acetal-type reactive salt chemical species allow the coexistence of functional groups that normally cannot coexist, the reactions using reactive salts have potential to change the retrosynthesis planned based on conventional reactions.

Aqueous enantioselective organocatalytic Diels-Alder reactions employing hydrazide catalysts. A new scaffold for organic acceleration

[reaction: see text] Cyclic hydrazides function as asymmetric organocatalysts in aqueous Diels-Alder reactions. The hydrazide is employed as the catalytic machinery in a compact camphor-derived framework that imparts facial selectivity to the cycloadditions. Kinetic evidence suggests the reaction involves rapid iminium formation.

[Development of highly stereoselective reactions using lone pairs of oxygen atoms]

Highly stereoselective reactions have been developed using lone pairs of oxygen atoms, in other words, the nucleophilic ability of oxygen atoms. They consist of five types of reactions: 1) asymmetric synthesis using acetals, 2) organic reactions via Beckmann fragmentation intermediates, 3) organic reactions via dication equivalents, 4) rearrangement of 2,3-epoxy-1-alcohol derivatives, and 5) organic reactions using orthoesters. In this review, asymmetric syntheses using acetals are described in detail. They are divided into four categories: 1) diastereoselective 1,2-addition(alkylation, reduction) to the alpha-keto acetals and their derivatives, 2) asymmetric carbon-carbon bond formation by a combination of Beckmann fragmentation and asymmetric synthesis using C2-symmetric chiral acetals, 3) asymmetric synthesis via chiral oxonium ions prepared by intramolecular haloetherification of chiral ene acetals having C2-symmetric hydrobenzoin, and 4) asymmetric desymmetrization of meso-1,2-, meso-1,3-, and meso-1,4-diols via chiral oxonium ions prepared by intramolecular haloetherification of chiral ene acetals derived from optically pure norbornen aldehyde derivatives, and their applications to asymmetric syntheses of biologically active natural products.

Asymmetric Desymmetrization Based on an Intramolecular Haloetherification: A Highly Effective and Recyclable Chiral Nonracemic Auxiliary, 2-exo-Methyl-3-endo-phenyl-5-norbornene-2-carboxaldehyde, formeso-1,3- andmeso-1,4-Diols

A new chiral auxiliary, a 3-endo-phenyl norbornene aldehyde derivative, which is a crystalline, very stable, and easily handled, was developed for the desymmetrization of meso-1,3- and meso-1,4-diols. The key step of the method, an intramolecular bromoetherification, proceeded in a highly diastereoselective manner. A four-step sequence, 1) acetalization, 2) intramolecular bromoetherification followed by acid hydrolysis, 3) protection of the alcohol, and 4) retrobromoetherification, transformed the meso-diols into optically active derivatives. The 3-endo-phenyl norbornene aldehyde derivative was simultaneously reformed and could be used repeatedly. This is the first chemical example of a single auxiliary that is applicable for highly enantioselective desymmetrization of meso-1,3- and meso-1,4-diols; to the best of our knowledge, this is the best chemical method available for the desymmetrization of meso-1,4-diols.