Showing papers by "Keiichiro Fukumoto published in 1987"

Stereocontrolled construction of octahydroquinolizines, octahydroindolizines, hexahydrobenzo[a]quinolizines, and an octahydroindolo[2,3-a]quinolizine by an intramolecular double Michael reaction: synthesis of (±)epilupinine

Abstract: Stereocontrolled one-step syntheses of octahydroquinolizine and octahydroindolizine derivatives from α,β-unsaturated enamide esters was achieved under two different conditions; heating in the presence of chlorotrimethylsilane, triethylamine, and zinc chloride at 180–185 °C, and treatment with dimethyl-t-butylsilyl trifluoromethanesulphonate in the presence of triethylamine at –78 to 20 °C. A simple synthesis of an alkaloid, (±)-epilupinine, was accomplished. Hexahydrobenzo[a]-quinolizin-4-ones and an octahydroindolo[2,3-a]quinolizin-4-one were also constructed by the same method.

1,2-Asymmetric induction in intramolecular Michael reaction. A novel and enantioselective route to (+)-Geissman lactone

Abstract: The Horner-Emmons reaction of the hemiacetal (19), derived from L-(+)-diethyl tartrate, was found to give the pyrrolidine (21)via an intramolecular Michael reaction as a mixture of diastereoisomers which, after treatment with ethanethiol and boron trifluoride–diethyl ether, was converted into the lactone (22) and the ester (23). The lactone (22), a minor component, could then be transformed into the Geissman lactone (10), a potential precursor for retronecine synthesis, via a three-step sequence. Alternatively, the hemiacetal (41), prepared from S-(–)-malic acid, was converted into the Z-α,β-unsaturated ester (49) whose intramolecular Michael reaction followed by cleavage of the corresponding methoxymethyl ether afforded the pyrrolidine (51) as a major product in a highly diastereoselective manner. The three-step conversion of (51) into (–)-ethyl 3-oxo-2-oxa-6-azabicyclo[3.3.0]octane-6-carboxylate (32) provided an efficient and stereocontrolled route to the Geissman lactone in optically active form.

Application of a tandem electrocyclic [3,3]sigmatropic reaction of o-quinodimethane to the synthesis of calabar bean alkaloids. Part 2. First total synthesis of (±)-geneserine

Abstract: The first total synthesis of the Calabar bean alkaloid geneserine (1) starting with 1-cyano-5-methoxybenzocyclobutene (7) has been accomplished via a 16-step sequence in 27% overall yield. The key step in the synthetic strategy involves the tandem electrocyclic [3,3]sigmatropic reaction of the o-quinodimethane generated in situ by thermolysis of the benzocyclobutene (4), which affords quantitatively the isochroman-3-one (5). After the conversion of (5) into the oxindole (6), the pivotal intermediate for our strategy, differential functionalisation of this system provides the hydroxylamine (19) which has finally been converted into (±)-geneserine by treatment with di-isobutylaluminium hydride.

Enantioselective synthesis of useful chiral precursors, unsymmetrical propane-1,3-diol derivatives, from malonic acid

Abstract: Syntheses of chiral synthons via monosubstituted malonic chiral half esters were studied and chiral 3-silyloxypropanols were enantioselectively synthesised.

A novel approach to estranes by an intramolecular double Michael reaction

Abstract: A new construction of the estrane ring system was achieved by intramolecular double Michael reaction of the α,β-unsaturated enone ester (5).

Preferential Electrocyclic Reaction of o-Quinodimethane. New Route to Dihydronaphthalenes and Naphthalenes

Abstract: Substituted dihydronaphthalenes and naphthalenes are obtained via a preferential electrocyclic reaction of o-quinodimethanes generated by the thermolysis of 1-alkyl-1-alkenylbenzocyclobutenes.

Complementary Electrocyclic Reactions of o-Quinodimethanes. Highly Efficient Access to 4-Alkylideneisochroman-3-ones and 1-Carbomethoxy-3,4-dihydronaphthalenes

Abstract: Thermolysis of 1-alkenylbenzocyclobutenyl-1-carboxylic acid produced 4-alkylideneisochroman-3-ones in good yields via an unprecedented tandem electrocyclic-[1,5]sigmatropic process of o-quinodimethane. Alternatively, thermolysis of the corresponding methyl ester afforded the dihydronaphthalenes via E-transition state in excellent yields.

Stereocontrolled Construction of Octahydroquinolizines, Octahydroindolizines, Hexahydrobenzo(a)quinolizines, and an Octahydroindolo(2,3-a)quinolizine by an Intramolecular Double Michael Reaction: Synthesis of (.+-.)-Epilupinine.

Abstract: Stereocontrolled one-step syntheses of octahydroquinolizine and octahydroindolizine derivatives from α,β-unsaturated enamide esters was achieved under two different conditions; heating in the presence of chlorotrimethylsilane, triethylamine, and zinc chloride at 180–185 °C, and treatment with dimethyl-t-butylsilyl trifluoromethanesulphonate in the presence of triethylamine at –78 to 20 °C. A simple synthesis of an alkaloid, (±)-epilupinine, was accomplished. Hexahydrobenzo[a]-quinolizin-4-ones and an octahydroindolo[2,3-a]quinolizin-4-one were also constructed by the same method.

1,2‐Asymmetric Induction in Intramolecular Michael Reaction. A Novel and Enantioselective Route to (+)‐Geissman Lactone.

Abstract: The Horner-Emmons reaction of the hemiacetal (19), derived from L-(+)-diethyl tartrate, was found to give the pyrrolidine (21)via an intramolecular Michael reaction as a mixture of diastereoisomers which, after treatment with ethanethiol and boron trifluoride–diethyl ether, was converted into the lactone (22) and the ester (23). The lactone (22), a minor component, could then be transformed into the Geissman lactone (10), a potential precursor for retronecine synthesis, via a three-step sequence. Alternatively, the hemiacetal (41), prepared from S-(–)-malic acid, was converted into the Z-α,β-unsaturated ester (49) whose intramolecular Michael reaction followed by cleavage of the corresponding methoxymethyl ether afforded the pyrrolidine (51) as a major product in a highly diastereoselective manner. The three-step conversion of (51) into (–)-ethyl 3-oxo-2-oxa-6-azabicyclo[3.3.0]octane-6-carboxylate (32) provided an efficient and stereocontrolled route to the Geissman lactone in optically active form.

Enantioselective Synthesis of Useful Chiral Precursors, Unsymmetrical Propane-1,3-diol Derivatives, from Malonic Acid.

Abstract: Syntheses of chiral synthons via monosubstituted malonic chiral half esters were studied and chiral 3-silyloxypropanols were enantioselectively synthesised.

A Stereoselective Total Synthesis of 11-Oxoprogesterone, a Precursor to the Corticosteroids, via an Intramolecular Cycloaddition Reaction.

Abstract: A Stereoselective synthesis of 11-oxoprogesterone (pregn-4-ene-3,11,20-trione)(21) has been achieved via 19-norpregna-4,9(10)-diene-3,20-dione (14) and pregna-4,9(10)-diene-3,20-dione (18). The compound (14) was derived from the des-A,B-aromatic steroid (6), which was, in turn, constructed in a stereoselective manner via(3) by the thermolysis of the olefinic benzocyclobutene (2).