Aspects of chirality in overcrowded bistricyclic enes

Intramolecular overcrowding in bistricyclic enes (1) requires out-of-plane deformations in order to accommodate the sterically demanding tricyclic moieties without prohibitively close contacts of nonbonded atoms, The nonplanarity of 1 introduces the notion of chirality to the arena of overcrowded aromatic enes, Deviation from coplanarity occurs by twisting around the double bond and out-of-plane bending (hence pyramidalization). The bending is realized by folding of the tricyclic moieties, The conformations of homomerous (1, X = Y) and heteromerous (1, X not equal Y) bistricyclic enes and their mono- and disubstituted derivatives are analyzed along with their point group symmetries and chirality, The implications are illustrated using the structures of characteristic examples calculated with the semiempirical method PM3. (C) 1995 Wiley-Liss, Inc.