Showing papers by "Keiichiro Fukumoto published in 1998"

Palladium-Catalyzed Intramolecular Allylic Alkylation Reaction in Marine Natural Product Synthesis: Enantioselective Synthesis of (+)-Methyl Pederate, a Key Intermediate in Syntheses of Mycalamides.

Abstract: A novel preparation of (+)-methyl pederate (4), a key intermediate in syntheses of mycalamides (1), marine natural products from a New Zealand sponge of the genus Mycale, is described. The key step involves palladium-catalyzed intramolecular allylic alkylation of the carbonate 21, derived from (+)-(4R,5R,E)-5-(tert-butyldimethylsiloxy)-4-methyl-2-hexenol (13), yielding lactones 5 in 87% yield. Demethoxycarbonylation of the cyclization products 5 and further functional group transformations led to (+)-methyl pederate (4).

Influence of a 2‐Fluoro Substituent on Diastereoselectivity in the 1,3‐Dipolar Cycloadditions of Nitrones.

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.