The diastereoselectivity of zirconium alkoxide catalysed Meerwein-Ponndorf-Verley reductions

✍ Scribed by Krohn, Karsten ;Knauer, Birgit

• Publisher: John Wiley and Sons
• Year: 1995
• Tongue: English
• Weight: 529 KB
• Volume: 1995
• Category: Article
• ISSN: 0947-3440
• DOI: 10.1002/jlac.1995199507179

✦ Synopsis

Abstract

The new variation of the Meerwein‐Ponndorf‐Verley reduction using 1‐[4‐(dimethylamino)phenyl]ethanol (DMAPE) (6) or 1‐tetralol (12) (3 equiv.) as the reducing alcohols and Zr(O‐__t__Bu)~4~ as the catalyst (0.2 equiv.) is kinetically controlled and highly stereoselective. Preferential axial attack is achieved with the sterically less bulky alcohol 6 in the case of 4‐tert‐butyl‐ and 3‐methylcyclohexanones (1a → 96% axial and 3a → 93% axial attack). The combination tetralol (12)/Zr(O‐__t__Bu)~4~ behaves as a very bulky reducing agent, and the thermodynamically less stable alcohols 2c (80%) and 4c (92–96%) are formed preferentially in the reduction of 2a and 4b. The fused bicyclic systems 1‐methyl‐2‐tetralone (14a) and flavanone (15a) and the steroids 16a–18a are reduced with high stereoselectivity to the corresponding cis alcohols 14b and 15b and the (β‐alcohols 16b–18b. The stereochemical outcome is in agreement with the Felkin‐Ahn model.