Chiroptical properties of 2,3-dihydrobenzo[b]furan and chromane chromophores in naturally occurring O-heterocycles

The correlation between the helicity (absolute conformation) of the O-heterocyclic ring of chiral 2,3-dihydrobenzo [b]furan (1) and chromane (2) derivatives and their L-1(b) band CD was investigated. The same helicity rule was found for both unsubstituted chromophores: PIM helicity of the heterocyclic ring leads to a negative/ positive CD within the 1Lb band. While the substitution of the fused benzene ring by achiral substituents does not change this helicity rule for the chromane chromophore, it leads to its inversion for the 2,3-dihydrobenzo [b]furan chromophores. On the basis of these observations, the published absolute configurations of natural flavonol and pterocarpan derivatives were confirmed and the configurational assignments of several natural neolignans revised. (C) 2001 Wiley-Liss, Inc.