Itsuno-Corey Reduction
The Corey-Itsuno reduction, also known as the Corey-Bakshi-Shibata (CBS) reduction, is a chemical reaction used for the enantioselective reduction of prochiral ketones to produce non-racemic alcohols. This reaction is facilitated by a chiral oxazaborolidine catalyst, which is formed by the reaction of chiral amino alcohols with borane (BH3). The oxazaborolidine catalyst mediates the reduction by coordinating with the borane reagent, which then selectively delivers a hydride to the ketone, resulting in the formation of a chiral alcohol with high enantiomeric excess (ee)[1][3].
The reaction was first reported by Itsuno and coworkers, who used chiral alkoxy-amine-borane complexes for the reduction of ketones. Later, in 1987, E. J. Corey and coworkers developed the reaction further by generating oxazaborolidine products that catalyzed the enantioselective reduction rapidly[1].
The CBS reduction is a powerful method for reducing a wide range of ketones under anhydrous conditions, as the presence of water can significantly affect the reaction's outcome. The reaction proceeds via a six-membered transition state, where the borane reagent is activated by coordination to the Lewis basic nitrogen of the CBS catalyst. The ketone is then bound to the catalyst-borane complex at the sterically more accessible lone pair, leading to a face-selective intramolecular hydride transfer[3].
The CBS catalyst is known for its good air and moisture stability, although the reduction must be conducted under anhydrous conditions to prevent adverse effects on the reaction. When the oxazaborolidine has a rigid bicyclic structure, high enantiomeric excess can be achieved[3].
In summary, the Corey-Itsuno (CBS) reduction is a reliable and widely used method in organic chemistry for the enantioselective synthesis of alcohols from ketones, offering high levels of stereocontrol and broad applicability in the synthesis of pharmaceutical intermediates and other complex organic molecules[1][3].
Citations:
[1] https://en.wikipedia.org/wiki/Corey%E2%80%93Itsuno_reduction
[2] https://youtube.com/watch?v=jtYtlOU6zoI
[3] https://nrochemistry.com/corey-bakshi-shibata-reduction/
[4] https://www.organic-chemistry.org/namedreactions/corey-bakshi-shibata-reduction.shtm
[5] https://youtube.com/watch?v=yrRvU7TeyT8
[6] https://youtube.com/watch?v=8f94Qb2Jln0
[7] https://www.sciencedirect.com/topics/chemistry/corey-bakshi-shibata-reduction
[8] https://www2.chemistry.msu.edu/faculty/wulff/myweb26/Name%20Reactions_pdf/2009-02-27%20Nilanjana.pdf
[9] https://en.wikipedia.org/wiki/CBS_catalyst
[10] https://www.santiago-lab.com/reagent-of-the-month-cbs-oxazaborolidine/
[11] https://onlinelibrary.wiley.com/doi/10.1002/9783527675142.ch11
[12] https://synarchive.com/named-reactions/itsuno-corey-reduction
[13] https://www.researchgate.net/publication/263948733_Corey-Itsuno_Reduction_of_Ketones_A_Development_of_Safe_and_Inexpensive_Process_for_Synthesis_of_Some_API_Intermediates
[14] https://www.ncbi.nlm.nih.gov/pmc/articles/PMC6222374/
[15] https://wikidata.org/wiki/Q903598