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(5 H)-ones

Abstract

Glyoxalic, phenylglyoxalic and pyruvic acids 1a– c undergo regio- and diastereoselective indium mediated allylations with allyl and cinnamyl bromides and ethyl 4-bromocrotonate to provide respective 2-allyl-, 2-(1-phenylallyl)- 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(5 H)-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 1H NMR spectra.