Kōichi Mikami

The [2,3]Wittig rearrangement of 2-alkenyloxyacetic acids and its applications to the stereocontrolled synthesis of β, γ-unsaturated aldehydes and conjugated dienoic acids☆

Abstract Dianions generated from 2-alkenyloxyacetic acids readily undergo the [2,3]sigmatropic rearrangement uhich can constitute the versatile synthetic sequences for the stereocontrolled synthesis of β,γ-unsaturated aldehydes and conjugated dienoic acids.

[2,3]-Wittig sigmatropic rearrangement of crotyl propargyl ether system. An emerging tool for control of acyclic stereochemistry

Abstract The [2,3]-Wittig rearrangement of properly designated ( E )- and ( Z )-crotyl propargyl ether system has been shown to exhibit a remarkably high degree of threo - and erythro -selection, respectively, and the stereochemical outcomes are discussed on mechanistic grounds. Some useful transformations of the rearrangement product are also described within the context of the formal total synthesis of (±)-oudemansin. Further, the high level of diastereoselection is maintained in the reaction of the α-methylcrotyl counterparts, together with the exclusive formation of the ( E )-olefinic bond.

Acyclic stereocontrol via asymmetric [2,3]-Wittig rearrangement with high enantio- and erythro-selectivity and its use in the chiral synthesis of insect pheromones

Abstract Such an asymmetric [2,3]-Wittig variant that is both highly enantio- and erythro-selective is described within the context of the chiral synthesis of the insect pheromones, (3 S , 4 S )-4-methyl-3-heptanol and ( S )-4-methyl-3-heptanone.

Diastereocontrol via Lewis acid-promoted ene reaction with glyoxylates and its application to stereocontrolled synthesis of a 22R-hydroxy-23-carboxylate steroid side chain

Abstract Taking the judicious choice of the Lewis acid employed, the glyoxylate ene reactions are shown to proceed with a high level of either erythro or threo diastereoselection. The utility of the ene methodology is demonstrated through the stereocontrolled synthesis of a 22 R -hydroxy-23-carboxylate steroid side chain.

Diastereocontrol via the phenol- and palladium(II)-catalyzed Claisen rearrangement with cyclic enol ethers

Abstract Taking the judicious choice of either 2,6-dimethylphenol or PdCl 2 (RCN) 2 as the catalyst, the Claisen rearrangements with the enol ethers of cyclic ketones are shown to proceed with a high level of either anti or syn diastereoselection, respectively.

Asymmetric allylsilane-mediated carbocyclization: A highly enantiospecific synthesis of (1S, 2S)-(+)-2-methyl-3-cyclopenten-1-ol

An enantiospecific synthesis of the title compound is described which involves the TiCl4-promoted cyclization of the chiral allylic silane having formyl group, which was obtained via the Claisen rearrangement of (R, E)-1-trimethylsilyl-1-buten-3-ol.

Stereocontrolled synthesis of either (22S)- or (22R)-hydroxy-23-acetylenic steroid side chains via [2,3]-Wittig sigmatropic rearrangement

Abstract A unified approach to either (22 S )- or (22 R )-hydroxy-23-acetylenic steroid side chains is described which relies on the concept of the stereochemical transmission via the [2,3]-Wittig sigmatropic rearrangement.

Intramolecular acylation of vinylic silanes. A novel, general approach for the synthesis of four- to six-membered carbocyclic systems and its regiochemical features

Abstract Intramolecular acylations of m-trimethylsilyl-m-alkenoyl chlorides (m = 4 and 5) are described which afford the expected α-alkylidenecycloalkanone and/or the unexpected cycloalkenone, depending upon the substrate structure.

New sigmatropic sequences based on the [2,3]-wittig rearrangement of the bis-allylic ether system : A general approach to regiocontrolled c—c bond formation of allylic moieties leading to unsaturated carbonyl compounds

Abstract Four new sigmatropic sequences triggered by the regiocontrolled [2,3]-Wittig rearrangement of unsymmetrical bis-allylic ethers (1) to the l,5-dien-3-ols (2) arc described, which provide unique, regiocontrolled methods for the synthesis of a wide variety of unsaturated carbonyl compounds possessing interesting molecular frameworks. The newly developed sequences include the [2,3]-Wittig-Claisen, the tandem [2,3]-Wittig-oxy-Cope, the tandem oxy-Cope-Claisen, and the tandem oxy-Cope-Cope sequences.

Sequential Claisen-ene approach to carbocyclization: a new entry to a steroid C/D ring synthon

Abstract A new and facile entry to a steroid C/D ring synthon is described which relies on the sequential combination of the Claisen rearrangement with the intramolecular ene reaction involving an acetylenic bond with methoxycarbonyl group as the enophile.