Showing papers by "Keiichiro Fukumoto published in 1997"
31 citations
TL;DR: In this paper, the role of 1,2-asymmetric induction on the 1,3-dipolar cycloaddition of nitrones is influenced by the presence of a fluorine atom at the C 2 position.
Abstract: It is clear that the role of 1,2-asymmetric induction on the 1,3-dipolar cycloaddition of nitrones is influenced by the presence of a fluorine atom at the C-2 position. 2-Fluoro nitrones, synthesized by three different methods, have been subjected to the intermolecular 1,3-dipolar cycloaddition with ethyl vinyl ether. The stereostructures of isoxazolidines formed were determined by their conversion into 2,7-dioxa-6-azabicyclo[3.2.1]octanes. The diastereoselectivity of 2-fluoro nitrones was the reverse of that of the corresponding 2-hydro nitrones. This fact supports that the conformation with relief from the dipole repulsion between the fluorine atom and the oxygen atom of the nitrone is a preferred one for 2-fluoro nitrones, while the corresponding 2-hydro nitrones adopt the conformation with the least 1,3-allylic strain.
13 citations
TL;DR: In this article, the total synthesis of (±)-cedranediol (7 ) was achieved using intramolecular double Michael reaction using intrapolynomial double-Michael reaction.
10 citations
8 citations
TL;DR: In this paper, an intramolecular aldol reaction of keto acetals was performed with Me3SiI−(Me3Si)2NH====== leading to spirobicyclic compounds.
Abstract: An intramolecular aldol reaction of keto acetals 1, regioselectively
performed with Me3SiI–(Me3Si)2NH
leading to spirobicyclic compounds 2 and 3, has been applied to the
syntheses of (±)-spirojatamol and
(±)-erythrodiene.
6 citations
TL;DR: In this paper, the product was converted into the synthetic intermediate 7 of quinine alkaloids and the synthetic precursor 19 of (+)-dihydroantirhine 10.
Abstract: (4R,5R)-2-Ethoxy-5-ethyl-4-methoxycarbonylmeth
yl-3,4,5,6-tetrahydro-2H-pyran 3, which has been
enantioselectively prepared, is converted into the
cis-substituted lactone 11 by treatment with propanedithiol in
the presence of boron trifluoride–diethyl ether. The product 11 is
converted into the synthetic intermediate 7 of quinine alkaloids and the
synthetic precursor 19 of (+)-dihydroantirhine 10.
5 citations
2 citations
TL;DR: In this paper, the total synthesis of (±)-cedranediol (7 ) was achieved using intramolecular double Michael reaction using intrapolynomial double-Michael reaction.
Abstract: Total synthesis of (±)-cedranediol ( 7 ) was achieved using intramolecular double Michael reaction. Heating the enone 10 together with ZnCl 2 , Et 3 N, and TMSCl gave the tricyclo[5.2.1.0 1,5 ]decane 9 as a single diastereomer, which was converted into (±)-cedranediol ( 7 ).
1 citations
TL;DR: In this article, an intramolecular aldol reaction of keto acetals was performed with Me3SiI−(Me3Si)2NH====== leading to spirobicyclic compounds.
Abstract: An intramolecular aldol reaction of keto acetals 1, regioselectively
performed with Me3SiI–(Me3Si)2NH
leading to spirobicyclic compounds 2 and 3, has been applied to the
syntheses of (±)-spirojatamol and
(±)-erythrodiene.
TL;DR: In this article, the product was converted into the synthetic intermediate 7 of quinine alkaloids and the synthetic precursor 19 of (+)-dihydroantirhine 10.
Abstract: (4R,5R)-2-Ethoxy-5-ethyl-4-methoxycarbonylmeth
yl-3,4,5,6-tetrahydro-2H-pyran 3, which has been
enantioselectively prepared, is converted into the
cis-substituted lactone 11 by treatment with propanedithiol in
the presence of boron trifluoride–diethyl ether. The product 11 is
converted into the synthetic intermediate 7 of quinine alkaloids and the
synthetic precursor 19 of (+)-dihydroantirhine 10.
TL;DR: In this article, the complete stereocontrolled synthesis of angularly disubstituted cis-decalins based on the sequenced radical ring expansion and cyclization process of α-iodomethylcyclopentanones 1 and 6 is described and the stereochemical outcome of this radical reaction is also discussed.
Abstract: The complete stereocontrolled synthesis of angularly disubstituted cis -decalins based on the sequenced radical ring expansion and cyclization process of α-iodomethylcyclopentanones 1 and 6 is described and the stereochemical outcome of this radical reaction is also discussed. The compounds 2–5 and 7–13 thus prepared could be versatile intermediates for the synthesis of biologically important compounds.
TL;DR: In this article, simple and highly effective methods for the synthesis of polycyclic ring systems via two types of intramolecular domino reactions are developed and presented, and some related reactions of these methods are described.
Abstract: Simple and highly effective methods for the synthesis of polycyclic ring systems via two types of intramolecular domino reactions are developed and presented. The first example is an intramolecular double Michael reaction, whose scope-limitation, mechanism and application to natural product synthesis are discussed. The intramolecular Michael-aldol reaction is the second case, which provides a nice method for the preparation of polycyclic compounds having a four-membered ring system. In addition, some related reactions of these methods are described.