ASPECTS OF CHIRALITY IN OVERCROWDED BISTRICYCLIC ENES

Intramolecular overcrowding in bistricyclic enes (1) requires out-of-p lane deformations in order to accommodate the sterically demanding tri cyclic moieties without prohibitively close contacts of nonbonded atom s, The nonplanarity of 1 introduces the notion of chirality to the are na of overcrowded aromatic enes, Deviation from coplanarity occurs by twisting around the double bond and out-of-plane bending (hence pyrami dalization). The bending is realized by folding of the tricyclic moiet ies, The conformations of homomerous (1, X = Y) and heteromerous (1, X not equal Y) bistricyclic enes and their mono- and disubstituted deri vatives are analyzed along with their point group symmetries and chira lity, The implications are illustrated using the structures of charact eristic examples calculated with the semiempirical method PM3. (C) 199 5 Wiley-Liss, Inc.