PyBOX represents a very important subgroup of bis(oxazoline) (BOX) ligands for asymmetric synthesis. Often in PyBOX two enantiomeric oxazoline rings containing a bulky substituent at the 4- and/or the 5-carbon positions are bridged with the pyridine, forming a C2 symmetrical molecule.
PyBOX is a tridentate “pincer-type” ligand and able to coordinate with a wide range of metals including alkaline earth, d- and f-transition metal atoms. Upon coordination of oxazoline rings through the N atoms, two stereogenic centers are produced near the metal centre. This can influence and control the enantioselective process.
Pyridine-linked bis(oxazoline) ligands were introduced by Hisao Nishiyama in 1989. He used RuCl3/(S)-(i-Pr)-PyBOX (07-0307) CAS 118949-61-4 catalyst for asymmetric hydrosilylation of ketones[2]. (R)-isomer of (i-Pr)-PyBOX (07-0306) CAS 131864-67-0 is also highly effective in enantioselective transformations, e.g. Mannich reaction[3].
Today PyBOX ligands exist with a wide range of structural diversities. Metal complexes incorporating Phenyl [(R,R)-Ph-PyBOX (07-0303) CAS 128249-70-7S,S)-Ph-PyBOX (07-0304)] CAS 174500-20-0 (R) 07-0390 CAS 365215-38-9 and (S) 07-0391] CAS 151670-69-8 and Indenyl-PYBOX (07-0280) CAS 185346-09-2 ligands are effective enantioselective catalysts for a variety of asymmetric synthesis.
For more detailed descriptions of each catalytic process please review the corresponding technical note for each item on our website.
References:
- Chem. Rev., 2006, 106, 3561.; Chem. Rev. 2011, 111, PR284
- Organometallics, 1989, 8, 846.
- Organometallics, 1991, 10, 500.
- Chem. Eur. J., 2013, 19, 10142.
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