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Diastereomers Composed of Two Planar‐Chiral Subunits: Bis([2.2]paracyclophan‐4‐yl)methane and Analogues
Author(s) -
Ernst Ludger,
Wittkowski Lars
Publication year - 1999
Publication title -
european journal of organic chemistry
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.825
H-Index - 155
eISSN - 1099-0690
pISSN - 1434-193X
DOI - 10.1002/(sici)1099-0690(199907)1999:7<1653::aid-ejoc1653>3.0.co;2-r
Subject(s) - diastereomer , chemistry , conformational isomerism , chirality (physics) , stereochemistry , planar chirality , axial chirality , nuclear magnetic resonance spectroscopy , crystallography , molecule , organic chemistry , enantioselective synthesis , catalysis , chiral symmetry , physics , quantum mechanics , nambu–jona lasinio model , quark
A series of compounds Q 2 Z was prepared, where Q = [2.2]paracyclophan‐4‐yl and Z = C(O) ( 4 ), CH 2 ( 5 ), SiMe 2 ( 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.