Chiroptical properties of a series of 3 and/or 4‐heterosubstituted 2(5H)‐furanones were investigated with respect to correlation with absolute configuration. The n − π* and π − π* Cotton effects have been assigned on the basis of comparison with the UV spectra in solvents of varying polarity. It is demonstrated that the n − π* transition in 4‐amino substituted 2(5H)‐furanones appears at shorter wavelength with respect to the π − π* transition. With the exception of 4‐pyrrolidino and 4‐benzylamino substituted 2(5H)‐furanones, other heterosubstituted 2(5H)‐furanones follow the butenolide configurational rule (Gawronski et al. J. Org. Chem. 61:1513–1515, 1996). Absolute configuration of 2(5H)‐furanone derivatives can also be assigned according to the sign of the Cotton effect (of unknown origin) at 200–230 nm. The structure of four representative sulfur and nitrogen substituted 2(5H)‐furanones has been analyzed by X‐ray diffraction. The results indicate planarity of the furanone ring and extended conjugation in 4‐amino substituted 2(5H)‐furanones. Chirality 9:537–544, 1997. © 1997 Wiley‐Liss, Inc.

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