A double iodoetherification of sigma-symmetric diene acetals for installing four stereogenic centers in a single operation: short asymmetric total synthesis of rubrenolide

Synthetic Approaches to α-, β-, γ-, and δ-lycoranes

Lycorane is a pentacyclic core presented in alkaloids isolated from the Amaryllidaceae family of herbaceous flowering plants. Members of this class of natural products have shown to display important biological properties including analgesic, antiviral, and antiproliferative activities. This review presents the known synthetic routes toward α-, β-, γ-, and δ-lycoranes. α-(19 routes), β-(10 routes), γ-(38 routes), and δ-(6 routes).

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.

Study on the total synthesis of velbanamine: Chemoselective dioxygenation of alkenes with PIFA via a stop-and-flow strategy

A "stop-and-flow" strategy was developed for the chemoselective dioxygenation of alkenes with a PIFA-initiated cyclization. This method is conceived for the desymmetrization of seco-diene, and a series of substituted 5-hydroxymethyl-γ-lactones were constructed after hydrolysis. This strategy also differentiates terminally substituted alkenes and constitutes a potentially novel synthetic approach for the efficient synthesis toward velbanamine.

Intramolecular iodoetherification of ene or diene ketals: facile synthesis of spiroketals

A novel and rapid approach to chiral mono- or di-substituted spiroketals based on remote asymmetric induction by intramolecular iodoetherification of ene or diene ketals has been developed. This strategy concisely offers 5,5- and 5,6-spiroketals including the natural insect pheromone of the wasp.

Electrophile-induced ether transfer: a new approach to polyketide structural units

[Structure: see text] A strategically novel approach to the formation of syn-1,3-diol mono- and diethers through electrophilic activation of homoallylic alkoxymethyl ethers has been developed. The resulting polyketide-like synthetic fragments are generated in good yield and with excellent stereocontrol. A chairlike transition state is proposed to account for the high stereoselectivity. Varying the conditions of the reaction workup results in the efficient generation of mono- and diether containing structural units common to polyketide natural products.

Intramolecular bromo-amination of 1,4-cyclohexadieneaminal: one-pot discrimination of two olefins and concise asymmetric synthesis of (−)-γ-lycorane

The reaction of cyclohexa-2,5-dienyl-1-methylaldehyde and optically pure 1,2-diaryl-1,2-diamine followed by intramolecular bromo-amination produced a one-pot discrimination of two olefins in the cyclohexane system, which was used for the asymmetric synthesis of (-)-gamma-lycorane.

[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.

Mild and Efficient Removal of Hydroxyethyl Unit from 2-Hydroxyethyl Ether Derivatives Leading to Alcohols

[reaction: see text]. CAN is a good reagent for the transformation of 2-hydroxyethyl ether units to alcohols. Significantly, many functional groups can tolerate the reaction conditions, although they do not survive under many previously reported removal conditions. The reaction mechanism is clarified.