Structure, Conformation, Stereodynamics, Dimer Formation, and Absolute Configuration of Axially Chiral Atropisomers of Hindered Biphenyl Carbinols.

CAN 147:406360 AN 2007:970153 CAPLUS (COPYRIGHT (C) 2008 ACS ON SCIFINDER (R)) ABSTRACT NMR SPECTRA OF BIPHENYL DERIVS. BEARING A SINGLE CR2OH SUBSTITUENT IN THE ORTHO POSITION INDICATE THAT THEY EXIST AS SP (MORE STABLE) AND AP (LESS STABLE) CONFORMERS, DUE TO THE RESTRICTED ROTATION ABOUT THE AR-CR2OH BOND. WHEN R = ET (COMPD. 2) THE CORRESPONDING ROTATION BARRIER WAS DETD. (7.5 KCAL MOL-1) BY LINE SHAPE SIMULATION OF THE LOW-TEMP. NMR SPECTRA. INTRODUCTION OF THE PROCHIRAL I-PR GROUP IN THE POSITION 3' OF A BIPHENYL WITH THE CME2OH SUBSTITUENT IN THE POSITION 2 (4) ALLOWED THE DETN. OF THE ENANTIOMERIZATION BARRIER (DUE TO THE AR-AR BOND ROTATION) FOR THE STEREOLABILE AXIALLY CHIRAL ATROPISOMERS (13.95 KCAL MOL-1). DFT COMPUTATIONS OF THESE BARRIERS WERE ALL IN AGREEMENT WITH THE EXPTS. BIPHENYLS BEARING TWO CR2OH GROUPS IN THE 2,2' POSITIONS WERE FOUND TO EXIST AS CONFIGURATIONALLY STABLE ATROPISOMERS: WHEN R = ME (7) THEY WERE SEPD. BY ENANTIOSELECTIVE HPLC...