Diastereomers Composed of Two Planar-Chiral Subunits: Bis([2.2]paracyclophan-4-yl)methane and Analogues
                                
                                    
                                        作者:Ludger Ernst、Lars Wittkowski                                    
                                    
                                        DOI:10.1002/(sici)1099-0690(199907)1999:7<1653::aid-ejoc1653>3.0.co;2-r
                                    
                                    
                                        日期:1999.7
                                    
                                    A series of compounds Q(2)Z was prepared, where Q = [2.2]-paracyclophan-4-yl 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 (diastereomeric ratio ca. 7:3). Compound 8 possesses a pseudoasymmetric phosphorus centre 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/5c, 6m/6c, and 8c were directly determined by NMR spectroscopy, that of 4m/4c 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 were studied by molecular mechanics computations by using the MM3(94) program. An attempt was made to rationalize some chemical shift differences between diastereomers on the basis of the conformers predicted.