Diastereomers composed of two planar-chiral subunits: Bis([2.2]paracyclophan-4-yl)methane and analogues

A series of compounds Q(2)Z was prepared, where Q = [2.2]-paracyclophan-4-y l and Z = C(=O) (4), CH2 (5), SiMe2 (6), S (7), P(=O)OMe (8), and C(=O)C(=O ) (9). Because of the planar chirality of Q, these compounds occur as meso- (m) and chiral (c) diastereomers, which were formed in equal amounts. They were separated in the cases of 4-7 and enriched in the case of 9 (diastere omeric ratio ca. 7:3). Compound 8 possesses a pseudoasymmetric phosphorus c entre and occurs as one chiral (8c) and two meso diastereomers (8m(1), 8m(2 )), all three of which were isolated separately. The configurations of 5m/5 c, 6m/6c, and 8c were directly determined by NMR spectroscopy, that of 4m/4 c indirectly by reducing the separated compounds to 5m and 5c, respectively , and that of 7m by X-ray diffraction. The favoured conformations of 4-8 we re studied by molecular mechanics computations by using the MM3(94) program . An attempt was made to rationalize some chemical shift differences betwee n diastereomers on the basis of the conformers predicted.