Efficient regioselective aldol condensation of methyl ketones promoted by organoaluminum compounds,and its application to muscone synthesis

Regioselective aldol condensation of 2-octanone and 2-butanone at the methyl side proceeded in high yields using a system of dialkylaluminum phenoxide/tertiary amine. The intramolecular aldol condensation of 2,15-hexadecanedione was carried out by the same system, especially di-i-butylaluminum phenoxide/pyridine, to give dehydromuscone in 65% yield. Its hydrogenation afforded muscone (3-methylcyclopentadecanone).     

Robust and efficient, yet uncatalyzed, synthesis of trialkylsilyl-protected cyanohydrins from ketones

High-yielding cyanosilylation of ketones with NaCN and various chlorotrialkylsilanes in DMSO proceeds smoothly without catalysis to give silyl-protected ketone cyanohydrins. The unique role of DMSO consists in rendering naked cyanide anions that reversibly add to the C double bond O bond at the rate-determining step followed by fast trapping of the transient tertiary sodium cyanoalcoholates with chlorotrialkylsilanes or in situ generated cyanotrialkylsilanes. Preparatively, the reaction matches the best known catalytic cyanosilylation systems applying expensive Me(3)SiCN and demonstrates unprecedented efficiency in the synthesis of sterically congested trialkylsilyl-protected cyanohydrins.     

New synthetic method for orsellic acid type macrolides by intramolecular alkylation of protected cyanohydrin. The synthesis of (±)-zearalenone.

Zearalenone was synthesized by a general cyclization method of orsellic acid type macrolides having ketone moiety using the intramolecular alkylation of the protected cyanohydrin. This alkylation tolerates the presence of ester group and requires short reaction time.     

A new method for the synthesis of macrocyclic ketones

Summary We have described the synthesis of macrocyclic diacetylene ketones by oxidative condensation of aliphatic ,-diacetyiene ketones.     

Development of a novel synthetic method for ring construction using organometallic complexes and its application to the total syntheses of natural products

Organometallic complexes are useful tools in synthetic organic chemistry. We investigated a novel synthetic method for ring construction using organometallic complexes and synthesized natural products and biologically active substances using these methods. Metalacycles formed from an early transition metal and diene, enyne, and diyne are stable under the reaction conditions and they are easily converted into compounds with functional groups by the addition of various agents. We have developed a novel synthetic method of heterocycles from enyne and diene using Cp2ZrBu2. The total syntheses of (-)-dendrobine, (+/-)-mecembrane, and (+/-)-mecembrine were achieved using this procedure. To synthesize these natural products as a chiral form, a novel palladium-catalyzed asymmetric allylic amination was developed, and chiral 2-arylcyclohexenylamine derivatives were synthesized. From these compounds, the total syntheses of (-)-mesembrane, (-)-mesembrine, (+)-crinamine, (-)-haemanthidine, and (+)-pretazetine were achieved. By further development of this procedure, a chiral 2-siloxymethylcyclohexenylamine derivative could be synthesized and the novel synthesis of indole derivatives was developed from this compound. From this indole derivative, (-)-tsubifoline and (-)-strychnine were synthesized.     

The first intramolecular Heck-Matsuda reaction and its application in the syntheses of benzofurans and indoles

In this Letter, we report, for the first time, the development of an efficient method for the intramolecular Heck reaction of arenediazonium salts in the synthesis of benzofuran and indole derivatives. In addition, this methodology allowed the synthesis of a series of dihydrobenzofuran acetic acid derivatives via a domino Heck-Matsuda coupling-carbonylation reaction.     

Highly efficient alkylation to ketones and aldimines with Grignard reagents catalyzed by zinc(II) chloride

A highly efficient alkylation to ketones and aldimines with Grignard reagents in the presence of catalytic trialkylzinc(II) ate complexes derived from ZnCl2 (10 mol %) in situ was developed. This simple Zn(II)-catalyzed alkylation could minimize the well-known but serious problems with the use of only Grignard reagents, which leads to reduction and aldol side products, and the yield of desired alkylation products could be improved.     

An important role played dianiones in the highly efficient macrocycle formation by an intramolecular alkyltion method: application to the synthesis of zearalenone

A new synthetic method for macrolides based on intramolecular alkylation of dianions, generated from phenylthiomethyl group and protected cyanohydrin, is reported. The use of dianions for the cyclization has several characteristics features; (1) Control of the conformation fo the side-chain, (2) Protection of the ester from a nucleophilic attack, (3) Acceleration of the intramolecular reaction without using high dilution conditions. To prove these speculations, the alkylation using the dianions $\text{5}$ and $\text{6}$ was examined in the synthesis of zearalenone.     

Short, highly efficient syntheses of protected 3-azido- and 4-azidoproline and their precursors

[structure: see text] An improved synthesis of protected cis- and trans-3-azido-L-proline and cis- and trans-4-azido-L- and -D-proline is reported. These compounds have been synthesized from the corresponding hydroxyproline precursors using diphenylphosphoryl azide under Mitsunobu conditions. Short, highly efficient syntheses of these precursors are described, based on a new lactone-opening reaction and p-nitrobenzoate hydrolysis under very mild conditions.     

An efficient, economical synthesis of hydroxytyrosol and its protected forms via Baeyer-Villiger oxidation

An efficient and practical preparation of hydroxytyrosol and its orthogonally-protected forms was developed from inexpensive tyrosol. The utilization of Baeyer-Villiger oxidation enables the chemoselective introduction of a phenolic hydroxyl group in good yield.     

An efficient method for the synthesis of enol ethers and enecarbamates. Total syntheses of isoindolobenzazepine alkaloids, lennoxamine and chilenine

An efficient method for the synthesis of enol ethers and enecarbamates has been developed based on catalytic hydrosilane reduction of alpha-phosphonoxy enol ethers and alpha-phosphonoxy enecarbamates. This method has been applied to the total syntheses of two isoindolobenzazepine alkaloids, lennoxamine and chilenine.     

Synthesis of dehydroxy-trans-resorcylide by intramolecular alkylation of the protected cyanohydrin using a butadiene telomer as a building block

Dehydrroxy-trans-resorcylide ($\text{15}$) was synthesized by efficient intramolecular alkylation of the protected cyanohydrin. The butadiene telomer obtained by the palladium catalyzed reaction of butadiene with acetic acid was used as a suitable block of the carbocycle.     

A facile method for oxidation of primary alcohols to carboxylic acids and its application in glycosaminoglycan syntheses

A convenient two-step, one-pot procedure was developed for the conversion of primary alcohols to carboxylic acids. The alcohol was first treated with NaOCl and TEMPO under phase-transfer conditions, followed by NaClO2 oxidation in one pot. This reaction is applicable to a wide range of alcohols and the mild reaction conditions are compatible with many sensitive functional groups, including electron-rich aromatic rings, acid-labile isopropylidene ketal and glycosidic linkages, and oxidation-prone thioacetal, p-methoxybenzyl, and allyl moieties. Several glycosaminoglycans such as heparin, chondroitin, and hyaluronic acid oligosaccharides have been synthesized in high yields by using this new oxidation protocol.     

A three-carbon (n+1+2) ring expansion method for the synthesis of macrocyclic enones. Application to muscone synthesis

The three-carbon ring expansion methodology commences with the preparation of a cyclic allene (C9, C11, C13), readily available from the corresponding cycloalkene via dibromocarbene addition and subsequent treatment with methyllithium. Dichloroketene addition to the cyclic allene regioselectively provides the [2+2] cycloadduct, which is reductively dechlorinated with zinc in methanol. The resulting cyclobutanone is then catalytically hydrogenated; cyclobutanone ring opening is affected with trimethylsilyl iodide; immediate dehydroiodination of the resulting β-iodocycloalkanone with diazabicycloundecane (DBU) provides the corresponding macrocyclic enone. The 15-membered enone was converted to d,l-muscone with (CH₃)₂CuLi.     

A novel synthetic method of dihydro-4-pyrone derivatives and its application to the syntheses of ar-atlantone and (±)-ar-turmerone

Reaction of 1,3-dihalo-3-methy]-2-butanone with t-butyl acetoacetate (NaH) gave t-butyl 3,4-dihydro-2,2,6-trimethyl-4-oxo-2H-pyran-5-carboxylate via the Favorskii-type rearrangement. Michael addition of 4-methylphenyllithium (CuI) followed by ring cleavage with Me₃ SiCl-NaI in DMF or PrCN afforded ar-atlantone as well as (±)-ar-turmerone selectively.     

An efficient and straightforward access to sulfur substituted [2.2]paracyclophanes: application to stereoselective sulfenate salt alkylation

A straightforward and high-yielding access to various [2.2]paracyclophanes possessing a sulfur-based functional group is reported, the key step being a SEAr reaction mediated by a sulfonium salt. The versatility of the methodology was exemplified by an original application in sulfenate salt chemistry, from which a remarkable chirality transfer was observed.     

An efficient, asymmetric organocatalyst-mediated conjugate addition of nitroalkanes to unsaturated cyclic and acyclic ketones

5-Pyrrolidin-2-yltetrazole is a versatile organocatalyst for the asymmetric conjugate addition of nitroalkanes to enones. Using this catalyst, this transformation requires short reaction times, tolerates a broad substrate scope, and possibly proceeds via generation of an iminium species.