Asymmetric reduction of α-keto acetals with potassium 9-O-(1,2-isopropylidene-5-deoxy-D-xylofuranosyl)-9-boratabicyclo[3.3.1]nonane. Enantioselective synthesis of α-hydroxy acetals with high optical purities
✍ Scribed by Byung Tae Cho; Yu Sung Chun
- Publisher
- Elsevier Science
- Year
- 1994
- Tongue
- English
- Weight
- 226 KB
- Volume
- 5
- Category
- Article
- ISSN
- 0957-4166
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✦ Synopsis
Asymmetric reduction of a-keto acetals with a chiral borohydride, potassiun 9-0-(1~-isopropylidcnt-5-doxy-a-Dxylofuranosyl)-~~~clo[3.3.l]nonane in 'IHF at -78°C provided the corresponding a-hydn-rxy acetals with 87 -99 % ee. Optically active a-hydroxy aldehydes are useful chit-al building blocks for the preparation of natural products such as rhodianose,' rocellaric acid: lipoxine A,' e&brevicomine,' and amino sugars, including ristosamine and daunosamine. These chit-al synthons are generally obtained from natural precursors or microbial reduction of a-keto acetals6 and a-keto thioacetals.' One of the most convenient methods for the synthesis of these chiral a-hydroxy aldehydes may be asymmetric reduction of a-keto acetals or a-keto thioacetals. However, to the best of our knowledge, no reports for the asymmetric reduction using chiral hydride reagents are available. although a variety of the hydride reducing agents to give high optical induction for ketones has been rep~rted.~ Very recently, we repotted the preparation of a chiral bomhydride, potassiun 9-0(l&isopropylidene-5-deoxy-a-D-xylofuranosyl)-9-bordtabicylo[3.3.l]nonane (l), which showed high enantioselectivity for aromatic and hindered aliphatic ketones9 In the course of study on the asymmetric reduction of K xylida, 1