Showing papers by "Keiichiro Fukumoto published in 1990"

Asymmetric total synthesis of(–)-protoemetinol,(–)-protoemetine,(–)-emetine, and (–)-tubulosine by highly stereocontrolled radical cyclisations

Abstract: Both enantiomers of the menthyl half-esters (10) and (23) of ethylmalonic acid were converted into(+)-(4S,5R)-4-(2-benzyloxyethyl)-5-ethyl-3,4,5,6-tetrahydro-2-pyrone (18). A mixture of the trans-(18) and cis-lactones (19) in a ratio of ca. 4 : 1 was prepared by way of radical cyclisation of the (E)-α,β-unsaturated esters (16), while the former (18) was synthesised with high stereoselection by the cyclisation of the (Z)-esters (26). The lactone (18) was enantioselectively transformed into (–)-protoemetimol (5) and (–)-protoemetine (4), correlated to (–)-emetine (1) and (–)-tubulosine (3).

Synthesis of 2,6-disubstituted dihydronaphthalenes and naphthalenes by electrocyclic reaction of o-quinodimethane. A synthesis of (±)-naproxen

Abstract: A survey of the electrocyclic reactions of o-quinodimethanes generated in situ by the thermolysis of dihydrobenzocyclobutenes with a variety of olefinic substituents at C-1 is reported. These reactions provide convenient access to the 2,6-disubstituted dihydronaphthalenes (11) and the naphthalenes (12). Thermolysis of the benzocylobutenes (10) at 180 °C in the presence of manganese dioxide affords in good yields the 2,6-di- and 2,3,6-tri-substituted naphthalenes (12) and (16). The naphthalenes (12b,f,h) thus obtained were easily converted into (±)-naproxen (5).

Ring expansion of cyclopropylmethanols to cyclobutanes—an enantioselective total synthesis of (R)-(+)-dodecan-5-olide, and (S)-(+)- and (R)-(–)-5-[(Z)-dec-1-enyl]dihydrofuran-2(3H)-one

Abstract: A novel and convenient route to chiral cyclobutanones (8) and (9) by ring expansion of the Cyclopropylmethanols (6) and (7) was developed, leading to an enantioselective total synthesis of (R)–(+)-dodecan-5-olide (25), and (S)-(+)- and (R)–(-)-5-[(Z)-dec-1-enyl]dihydrofuran-2(3H)-one (35) and (36)(the pheromone of the Japanese beetle).

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).

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).

Asymmetric Total Synthesis of (-)-Protoemetinol, (-)-Protoemetine, (-)-Emetine, and (-)-Tubulosine by Highly Stereocontrolled Radical Cyclisations.

Abstract: Both enantiomers of the menthyl half-esters (10) and (23) of ethylmalonic acid were converted into(+)-(4S,5R)-4-(2-benzyloxyethyl)-5-ethyl-3,4,5,6-tetrahydro-2-pyrone (18). A mixture of the trans-(18) and cis-lactones (19) in a ratio of ca. 4 : 1 was prepared by way of radical cyclisation of the (E)-α,β-unsaturated esters (16), while the former (18) was synthesised with high stereoselection by the cyclisation of the (Z)-esters (26). The lactone (18) was enantioselectively transformed into (–)-protoemetimol (5) and (–)-protoemetine (4), correlated to (–)-emetine (1) and (–)-tubulosine (3).

Synthesis of 2,6-Disubstituted Dihydronaphthalenes and Naphthalenes by Electrocyclic Reaction of o-Quinodimethane. A Synthesis of (.+-.)-Naproxen.

Abstract: A survey of the electrocyclic reactions of o-quinodimethanes generated in situ by the thermolysis of dihydrobenzocyclobutenes with a variety of olefinic substituents at C-1 is reported. These reactions provide convenient access to the 2,6-disubstituted dihydronaphthalenes (11) and the naphthalenes (12). Thermolysis of the benzocylobutenes (10) at 180 °C in the presence of manganese dioxide affords in good yields the 2,6-di- and 2,3,6-tri-substituted naphthalenes (12) and (16). The naphthalenes (12b,f,h) thus obtained were easily converted into (±)-naproxen (5).

Enantioselective Synthesis of the Key Intermediate of a 1β-Methylcarbapenem Antibiotic by Way of Nitrone 1,3-Dipolar Cycloaddition.

Abstract: Synthesis of the key intermediate of the 1β-methylcarbapenem antibiotic (1) was investigated by way of inter- and intramolecular nitrone 1,3-dipolar cycloaddition. A highly enantioselective construction of (3S,4R)-(–-)-3-[(1R)-1-(t-butyldimethylsiloxy)ethyl]-4-[(1R)-1-(hydroxymethyl)ethyl]azetidin-2-one (2) was achieved via intramolecular cycloaddition of the nitrone (6).

A New Synthetic Route to 2-Hydroxynaphthalene-1-carboxylic Acid Derivatives. An Efficient Access to the Naphthalene Moiety of Neocarzinostatin Chromophore.

Abstract: Thermolyses of the 1-carbomethoxy-1-alkenyloxybenzocyclobutenes 4a–d produced the dihydronaphthalenes 7a–d via chemoselective electrocyclic reaction of E-o-quinodimethanes in good yields. Then, 7a,b,d were easily converted to the 2-naphthol 9 (R 1 =R 2 =H) by sequential dehydrogenation and deprotection. The method of conversion developed here has been successfully applied to an efficient synthesis of the methanolysis product 12 of neocarzinostatin chromophore 10 .