Regio- and stereochemical aspects in synthesis of 2-allyl derivatives of glycolic, mandelic and lactic acids and their iodocyclisations to 3-hydroxy-3,4-dihydrofuran-2(5H)-ones

摘要

Glyoxalic, phenylglyoxalic and pyruvic acids la-c undergo regio- and diastereoselective indium mediated allylations with allyl and cinnamyl bromides and ethyl 4-bromocrotonate to provide respective 2-allyl-, 2-(1-phenylailyl)- and 2+1-ethoxycarbonyl)allyl]derivatives of glycolic, mandelic and lactic acids 3-11. The reactions follow Cram's chelation model for allylation and give syn addition products as the major or the only products. Diastereoselective iodocyclisations of 3-8 and 10 provide 3-hydroxy-3,4-dihydrofuran-2(5H)ones (15-21), the stereochemical outcome, of which depends on the nature and position of the substituents on the substrate, choice of solvent and base. The relative stereochemistries have been ascertained by X-ray structure and NOE experiments and coupling constants in the H-1 NMR spectra. (c) 2005 Elsevier Ltd. All rights reserved.