Showing papers by "J. Cristobal Lopez published in 1994"

Serial Radical Cyclization of Pyranose-Derived Dienes in the Stereocontrolled Synthesis of Densely Functionalized Cyclohexanes. A Route to Woodward's Reserpine Precursor

Abstract: Serial radical 5-exo/6-exo cyclizations of a readily prepared hexopyranose derivative having unsaturations on-template at C-2 and off-template at C-7 lead to a tricyclic cage in which all but one of the stereocenters in an optically pure form of Woodward's densely functionalized carbocyclic precursor have been established, the «one» requiring an hydroxyl epimerization

Some studies on proximal addition–elimination procedures in intermolecular carbon–carbon bond-forming free radical reactions. Convenient synthesis of ethyl (E)-(ethyl 2,3,6,7,8-pentadeoxy-α-D-erythro-nona-2,7-dienopyranosid)uronate

Abstract: Et3B-Induced hydrostannation of ethyl propiolate with tributyltin hydride afforded a mixture of ethyl (Z)- and (E)-3-(tributylstannyl)propenoate which, after purification, could be used as such in radical carbon–carbon bond-forming reactions with iodides as the sources of the carbon radicals. The radical-coupling reactions took place without significant loss of yield or stereoselectivity when compared with the same reactions carried out with the pure (Z)-stannylacrylate. Use of ethyl (Z)-3-(phenylsulfanyl)propenoate in the presence of carbon-centred radicals, generated with Bu3SnH from alkyl iodides, resulted in the formation of reduced and coupled products where the intermediate β-phenylsulfanyl radicals had experienced hydrogen transfer from Bu3SnH rather than 1,2-elimination of phenylsulfanyl radicals.

Fine tuning of chemo- and stereo-selectivity in cyclization reactions of tethered radicals derived from 4-O-substituted-α-D-erythro-oct-2,6-dienopyranosides. Stereoselective access to carbocycles and branched-chain sugars

Abstract: Chemoselectivity in the radical cyclization of tethered α-D-erythro-oct-2,6-dienopyranosides can be accomplished by changes in the nature of the tether and/or in the oxidation state at the termini of the olefins, to afford stereoselectively 3-deoxy-3-C-substituted carbohydrates, off-template branched-chain sugars, or functionalized cyclopentanes.

Protecting group for acetals and methods of using the same in the activation of saccharides

Abstract: The present invention relates to a method of protecting the hemiacetal or acetal group at the anomeric carbon of a saccharide molecule comprising forming a 4-alkenyl glycoside or 4-alkenoyl glycosyl ester. The invention also relates to use of 4-alkenyl glycosides and 4-alkenoyl glycosyl esters in carbohydrate chemistry, including in the synthesis of oligosaccharides.