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

Glyoxalic, phenylglyoxalic and pyruvic acids 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 . The reactions follow Cramʹs chelation model for allylation and give syn addition products as the major or the only products. Diastereoselective iodocyclisations of and provide 3-hydroxy-3,4-dihydrofuran-2(5H)-ones (), 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.