Atsushi Abiko

Asymmetric catalytic cyclopropanation of olefins : bis-oxazoline copper complexes

Abstract Bis-oxazolines (1–7) prepared from diethyl malonate and chiral amino alcohols were converted into their Cu(II) complexes which, upon activation, exhibit high enantioselectivity of up to 99 %ee for catalytic cyclopropanation of olefins.

An improved, convenient procedure for reduction of amino acids to aminoalcohols : use of NaBH4-H2SO4

Abstract The use of NaBH4-H2SO4, For the reduction of α-amino acids to the corresponding aminoalcohols offers definite advantages: i) operational simplicity, ii) ease of scaling up the reaction without risking explosion, and iii) use of the inexpensive reagents.

KMnO4 revisited: Oxidation of aldehydes to carboxylic acids in the tert-butyl alcohol - aqueous NaH2PO4 system

Abstract Aldehydic compounds with one or more protected hydroxyl groups are effectively oxidized with KMnO4 to the corresponding carboxylic acids using a mixture of t -BuOH and aqueous NaH2PO4 as a reaction medium.

Synthesis of (+)-siphonarienone: Asymmetric alkylation using a chiral benzopyrano-isoxazolidine auxiliary

Abstract Asymmetric alkylation of the potassium enolates derived from N-propionyl benzopyrano-[4,3-c]-isoxazolidine derivatives with chiral alkyl triflates proceeded smoothly with high diastereoselectivity. The stereochemistry of the newly formed stereogenic center was fully controlled by the facial selectivity of the enolate according to the rule of double asymmetric synthesis. The application of this methodology led to the first synthesis of (+)-siphonarienone, a marine polypropionate natural product.

The asymmetric Horner-Emmons reaction using a benzopyrano-isoxazolidine auxiliary

Abstract The asymmetric Horner-Emmons reaction of the phosphonate derived from a chiral benzopyrano-isoxazolidine (with 4-substituted cyclohexanones) proceeded in high diastereoselectivity with the aid of KHMDS and 18-crown-6 ether. Enantiomerically pure, axially dissymmetric cyclohexylidene alcohols, aldehydes and ketones were obtained from the diastereomerically pure Horner-Emmons products in a single step.

NEW ISOXAZOLIDINE-BASED CHIRAL AUXILIARIES FOR ASYMMETRIC SYNTHESES

Abstract New chiral auxiliaries based on the bicyclic-isoxazolidine skeleton, 3-oxa-2,7-diazabicylo[3,3,0]octane derivatives, were synthesized in 60–80% overall yields from amino acids. Asymmetric alkylation and boron aldol reaction using the auxiliaries proceeded with high selectivities. “Carboxylic amide” has been used for the asymmetric boron-mediated aldol reaction for the first time.

Highly efficient resolution of benzopyrano[4,3-c]isoxazolidine derivatives: Versatile chiral auxiliaries for asymmetric alkylation

Abstract Benzopyrano[4,3-c]isoxazolidine derivatives, newly developed chiral auxiliaries for asymmetric alkylation, were synthesized and resolved in a unique manner. Resolution could be executed so efficiently that both enantiomers were obtained with a single resolving reagent in excellent yields.

Degradation of amphotericin B: Cleavage of the glycosidic linkage with aluminum amalgam [Al(Hg)] of dichlorodicyanoquinone (DDQ)

Abstract After appropriate protection of the hydroxyl and other functional groups present in amphotericin B, reductive and oxidative cleavages of the glycosidic linkage are effected with Al(Hg) and DDQ to obtain the C(1)-C(19) fragment and the C(19)-ketone correspondong to the aglycone, respectively.