Evans-Saksena Reduction
The Evans-Saksena reduction is a diastereoselective reduction of β-hydroxy ketones to the corresponding anti-dialcohols. The reaction employs the reagent tetramethylammonium triacetoxyborohydride (Me4NHB(OAc)3). This reduction was first described by Anil K. Saksena in 1983 and further developed by David A. Evans in 1987[2].
The reaction is thought to proceed through a 6-membered ring transition state. The intramolecular hydride delivery from the boron reducing agent forces the reduction to proceed in a certain direction, thus determining the diastereoselectivity[2]. This reduction method has been used in the synthesis of several products, particularly the bryostatins[2].
The Evans-Saksena reduction is a method for controlling the stereochemical outcome of the reduction of β-hydroxy ketones. It introduces a new stereogenic center into the molecule, and it is a substrate-controlled diastereoselective reduction[1].
The Evans-Saksena reduction can be contrasted with the Narasaka–Prasad reduction, which similarly employs a boron chelating agent but favors the corresponding syn-diol product[2].
In practical applications, the Evans-Saksena reduction has been used to reduce acyclic β-hydroxy ketones to their corresponding anti diols with high diastereoselectivity[3]. It has also been used in the synthesis of natural products and in the development of new synthetic methods[2][11].
Citations:
[1] http://chemweb.bham.ac.uk/coxlr/Teaching/4th_Year/II/Reduction_Reactions%20.pdf
[2] https://en.wikipedia.org/wiki/Evans%E2%80%93Saksena_reduction
[3] https://www.researchgate.net/figure/a-Substituted-P-Hydroxy-Ketone-Reductions-with-M-NHBOAC_tbl1_231445476
[4] https://www.wikidata.org/wiki/Q4371749
[5] https://www.youtube.com/watch?v=FNuma99tNvg
[6] https://www.ncbi.nlm.nih.gov/pmc/articles/PMC9901290/
[7] http://acl.digimat.in/nptel/courses/video/104105087/lec54.pdf
[8] https://pubs.rsc.org/en/content/articlepdf/2015/ob/c5ob00498e
[9] https://pubs.rsc.org/en/content/getauthorversionpdf/c6ra00653a
[10] https://en.wikipedia.org/wiki/Diol
[11] https://en.wikipedia.org/wiki/Evans%E2%80%93Tishchenko_reaction
[12] https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3050503/
[13] https://rushim.ru/books/mechanizms/reductions.pdf
[14] https://chemistry-europe.onlinelibrary.wiley.com/doi/full/10.1002/cbic.202200073
[15] https://journals.plos.org/plosmedicine/article?id=10.1371%2Fjournal.pmed.1001701
[16] https://core.ac.uk/download/pdf/131382648.pdf
[17] https://www.researchgate.net/publication/231445476_Directed_reduction_of_-hydroxy_ketones_employing_tetramethylammonium_triacetoxyborohydride
[18] https://pubs.acs.org/doi/10.1021/acs.orglett.1c02650
[19] https://pubs.rsc.org/en/content/articlehtml/2021/cc/d1cc00442e
[20] https://www.youtube.com/watch?v=KboFgUZSEzU
[21] https://etheses.whiterose.ac.uk/17392/1/Thesis%20newest-3-final.pdf
[22] https://chemistry-europe.onlinelibrary.wiley.com/doi/full/10.1002/chem.202202464