Showing papers by "Keiichiro Fukumoto published in 1991"

Stereoselective alkylation of dianions derived from chiral half-esters of monosubstituted malonic acids: asymmetric synthesis of α-alkyl α-amino acids and key synthetic intermediates for Hunteria and Aspidosperma indole alkaloids

Abstract: Substitution of the chiral half-esters of monosubstituted malonic acids with halides leads to the formations of mixtures of the diastereoisomeric alkyl- or benzyl-malonic half-esters. The (R)-isomers (13A and 15A–22A) were obtained from the phenylmenthyl half-ester 14 of methylmalonic acid in high diastereoisomeric excess. The same stereoisomers were also produced by reaction of the half-esters 9, 23 and 24 with methyl iodide. Their absolute configurations were determined by transforming the major products into the known α-alkyl α-amino acid derivatives 30, 33 and 35. The major product 43, prepared by allylation of the half-ester 9, was converted into two lactones 41 and 42, key intermediates for synthesis of indole alkaloids of the Hunteria and Aspidosperma types. The mechanism of the above alkylation is discussed.

A Novel Approach to Quaternary Substituted Chiral Cyclobutanes. A Formal Enantioselective Total Synthesis of 1,3-Dioxole Pheromone, (-)-Frontalin

Abstract: A novel synthesis of the quaternary substituted chiral cyclobutanone (9) was achieved by the concerted ring expansion of the chiral cyclopropyl epoxide (8) which lead to a formal total synthesis of (-)-frontalin (14)

A practical route for enantioselective total synthesis of (+)-11-deoxy-19-norcorticosterone via intramolecular Diels–Alder addition to an ortho-quinodimethane

Abstract: A convenient and practical route for enantioselective synthesis of the A-nor-B-trienic steroid 2via an intramolecular [4 + 2] cycloaddition of the olefinic ortho-quinodimethane 3 generated in situ by thermolysis of the olefinic benzocyclobutene 4 is reported. This leads to the total synthesis of (+)-11-deoxy-19-norcorticosterone 1 by use of a usual chemical manipulation on intermediate 2.

Asymmetric construction of α,α–disubstituted cyclobutanones–enantioselective total synthesis of (–)-frontalin

Abstract: Novel access to the chiral, α,α-disubstituted ketone 2-hydroxymethyl-2-methylcyclobutanone was developed, leading to an enantioselective total synthesis of (–)-frontalin, an aggregating pheromone of bark beetles.

A Facile and Enantioselective Total Synthesis of (+)‐19‐ Nordeoxycorticosterone.

Abstract: (+)-19-Nordeoxycorticosterone (1) has been synthesised by A-ring construction of the (+)-A-nor-B-trienic steroid (2) obtained enantioselectively from the alkenic benzocyclobutene (12).

Stereoselective Alkylation of Dianions Derived from Chiral Half‐Esters of Monosubstituted Malonic Acids: Asymmetric Synthesis of α‐ Alkyl α‐Amino Acids and Key Synthetic Intermediates for Hunteria and Aspidosperma Indole Alkaloids.

Abstract: Substitution of the chiral half-esters of monosubstituted malonic acids with halides leads to the formations of mixtures of the diastereoisomeric alkyl- or benzyl-malonic half-esters. The (R)-isomers (13A and 15A–22A) were obtained from the phenylmenthyl half-ester 14 of methylmalonic acid in high diastereoisomeric excess. The same stereoisomers were also produced by reaction of the half-esters 9, 23 and 24 with methyl iodide. Their absolute configurations were determined by transforming the major products into the known α-alkyl α-amino acid derivatives 30, 33 and 35. The major product 43, prepared by allylation of the half-ester 9, was converted into two lactones 41 and 42, key intermediates for synthesis of indole alkaloids of the Hunteria and Aspidosperma types. The mechanism of the above alkylation is discussed.

A Novel Approach to Quaternary Substituted Chiral Cyclobutanes. A Formal Enantioselective Total Synthesis of 1,3-Dioxole Pheromone, (-)- Frontalin.

Abstract: A novel synthesis of the quaternary substituted chiral cyclobutanone (9) was achieved by the concerted ring expansion of the chiral cyclopropyl epoxide (8) which lead to a formal total synthesis of (-)-frontalin (14)

A Practical Route for Enantioselective Total Synthesis of (+)‐11‐Deoxy‐ 19‐norcorticosterone via Intramolecular Diels‐Alder Addition to an ortho‐Quinodimethane.

Abstract: A convenient and practical route for enantioselective synthesis of the A-nor-B-trienic steroid 2via an intramolecular [4 + 2] cycloaddition of the olefinic ortho-quinodimethane 3 generated in situ by thermolysis of the olefinic benzocyclobutene 4 is reported. This leads to the total synthesis of (+)-11-deoxy-19-norcorticosterone 1 by use of a usual chemical manipulation on intermediate 2.

Homochiral Syntheses of (-)-Dihydrocorynantheol

Abstract: A Corynanthe-type indole alkaloid, (–)-dihydrocorynantheol (7), was enantioselectively synthesized from (+)-(4S,5R)-4-(2-benzyloxyethyl)-5-ethyl-3,4,5,6-tetrahydro-2-pyrone (3), derived from ethylmalonic acid. The synthetic compound (7) was identical in all respects with a sample prepared from yohimbine (8).