J. Cristobal Lopez

n-Pentenyl esters versus n-pentenyl glycosides. Synthesis and reactivity in glycosidation reactions

n-Pentenyl esters, which are readily obtained by mild esterification of the anomeric hydroxy group of sugars, can be efficiently used in glycosidation reactions, and they appear to be less prone to armed–disarmed phenomena than their n-pentenyl glycoside counterparts.

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

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

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.

The C4-exo methylene isomer of avermectin B1a: Synthesis via an allylic radical and bioactivity

Abstract Avermectin B1a Δ4,4a, 2, has been obtained from avermectin B1a, 1, and its bioactivity evaluated. The key step of the transformation is the reduction of an intermediate allylic radical with nBu3SnH.

Actinobolin and Bactobolin: Chemical Aspects and Syntheses

The discovery of a natural product with a novel carbon skeleton will undoubtedly challenge organic chemists to develop synthetic routes for its construction. If the natural product is complex, because of the presence of delicate functional groups and/or myriad chiral centers, the challenge becomes virtually irresistible. If the material displays biological activity, organic chemists will succumb to the challenge, and in time, a synthesis will be achieved.