CHIRAL 2-ARYL-2-METHYL-2H-1-BENZOPYRANS - SYNTHESIS, CHARACTERIZATIONOF ENANTIOMERS, AND BARRIERS TO THERMAL RACEMIZATION

The ease of thermal breaking of the C(sp(3))-O bond of the 2-aryl-2-me thyl-2H-1-benzopyrans 1-9 was evaluated by measuring the free energy ( Delta G(e)(not equal)) of the racemization reaction of optically activ e compounds. The variation of Delta G(e)(not equal) of the thermal rin g opening in terms of structural modifications is discussed. The synth esis of the studied compounds, the preparative separation of enantiome rs by liquid chromatography, the determination of enantiomeric purity, the circular dichroism of enriched enantiomers, and the measurement o f rate constants of enantiomerization by monitoring the decrease of th e polarimetric angle of rotation at suitable temperatures are describe d.