Stereoselective synthesis and molecular modeling of chiral cyclopentanes.

ABSTRACT

The reaction of 3-methyseleno-2-methylselenomethyl-propene with benzyl 2,3-anhydro-4-O-triflyl-ß-L-ribopyranoside provides a major convenient enantiomeric product of 1-methylene-(benzyl3,4-dideoxy-α-D-arabinopyranoso)-[3,4-c]-cyclopentane, with benzyl-2,3-anhydro-4-deoxy-4-C-(2-methyl- propen-3-yl)-α-D-lyxopyranoside as a minor product. While the reaction of 3-methyseleno-2-[methylselenomethyl]-propene with benzyl 2,3-anhydro-4-O-triflyl-α-D-ribopyranoside produces a good yield of benzyl-2,3-anhydro-4-deoxy-4-C-(2-methylpropen-3-yl)-α-D-lyxo-pyranoside. Molecular modeling and molecular dynamics simulations indicate that the intermediate in the reaction of the ß-L sugar frequently occupies an optimal conformation that leads to the formation of cyclopentane, while the intermediate in the reaction of the α-D sugar has a very small probability. The results point to the dominant role of the ß-L sugar intermediate in controlling the cyclopentane formation.