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TADDOLs under closer scrutiny – why bulky substituents make it all different
Author(s) -
Beck Albert K.,
Dobler Max,
Plattner Dietmar A.
Publication year - 1997
Publication title -
helvetica chimica acta
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.74
H-Index - 82
eISSN - 1522-2675
pISSN - 0018-019X
DOI - 10.1002/hlca.19970800708
Subject(s) - chemistry , conformational isomerism , ab initio , aryl , scrutiny , enantioselective synthesis , catalysis , selectivity , computational chemistry , potential energy surface , rotation (mathematics) , diffraction , stereochemistry , molecule , organic chemistry , quantum mechanics , alkyl , geometry , mathematics , political science , law , physics
A systematic investigation of the rotational behavior of aryl substituents in α,α,α′,α′‐ t etra a ryl‐1,3‐ d ioxolane‐4,5‐ d imethan ol s (TADDOLs) is presented. In the use as chiral ligands for enantioselective metal‐catalyzed reactions, a change from phenyl to bulkier substituents, e.g. , 1‐naphthyl, gives rise to an astounding alteration of the selectivity, The possible existence of preferred rotamers of TADDOLs has so far not been given due attention, which encouraged us to look at the validity of the Knowles model, originally formulated for diaryl substituted bisphosphines. 1 H‐NMR Investigations at various temperatures as well as X‐ray powder diffraction were employed to study the rotation in the case of tetra(1‐naphthyl) TADDOL 1. To support the interpretation of the experimental results, molecular mechanics, semiempirical, and ab initio calculations were performed. For comparison, the energy surface of tetraphenyl TADDOL 2 was calculated as well. Our results lead to the conclusion that for 1 , only one major conformation is present in both solution and solid state, which determines the stereochemical outcome of the catalyzed reactions.