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-heter ocyclic ring of chiral 2,3-dihydrobenzo [b]furan (1) and chromane (2) deriv atives and their L-1(b) band CD was investigated. The same helicity rule wa s found for both unsubstituted chromophores: PIM helicity of the heterocycl ic ring leads to a negative/ positive CD within the 1Lb band. While the sub stitution 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 obse rvations, the published absolute configurations of natural flavonol and pte rocarpan derivatives were confirmed and the configurational assignments of several natural neolignans revised. (C) 2001 Wiley-Liss, Inc.