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DOI: 10.1055/s-2004-831197
Efficient Activation of Zinc: Application of the Blaise Reaction to an Expedient Synthesis of a Statin Intermediate
Publication History
Publication Date:
26 August 2004 (online)
Abstract
Efficient and practical in situ zinc activation was accomplished by treatment with catalytic amount of an organic acid. The protocol was applied successfully to the Blaise reaction of various nitriles. Noteworthy is the excellent Blaise transformation of (S)-4-chloro-3-trimethylsilyloxybutyronitrile (2b) into tert-butyl (S)-6-chloro-5-hydroxy-3-oxohexanoate (1), a key intermediate for the preparation of HMG-CoA reductase inhibitors (statins).
Key words
in situ zinc activation - Blaise reaction - statin intermediate
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In the literature, iodine and 1,2-dibromoethane were used as in situ zinc activators. However, iodine and 1,2-dibromoethane were found to be deleterious for the Blaise reaction of benzonitrile with ethyl bromoacetate. Only 30% and 18% of respective conversion were observed.
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About 7-8 mol% of trimethylsilyl chloride was used for the activation of zinc. Under these conditions, complete conversion of the Blaise reaction of benzonitrile with ethyl bromoacetate was observed.
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The activation method was applied successfully to the Reformatsky reactions of benzaldehyde and nonanal with ethyl bromoacetate (1.3 equiv) in benzene to provide 79% and 78% of the corresponding β-hydroxy esters, respectively. For the Reformatsky reaction, benzene was found to be the choice of solvent. Use of THF has resulted in low yield.
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