Abstract
Catalytic Asymmetric allylation of aldehydes with functionalized allylic reagents represents an important process in synthetic organic chemistry because the resulting chiral homoallylic alcohols are valuable building blocks in diverse research fields. Despite the obvious advantages of allyl halides as allylation reagent under Barbier-type conditions, catalytic asymmetric version using functionalized allyl halides remains largely underdeveloped. Here, we addressed this issue by employing a chromium-catalysis system. The use of readily available allyl bromides with γ substitutions including trimethylsilyl, fluorinated methyl and phenylthio groups provided an efficient and convenient method to introduce those privileged functionalities into homoallylic alcohols. Good yields, high anti-diastereo- and excellent enantioselectivities were achieved under mild reaction conditions.
Highlights
Carbonyl allylation with functionalized allyl reagents has been a sustained research topic, as in this transformation, two new functionalities including one alcohol and a terminal C-C double bond are generated[1]
In line with our interests in the asymmetric carbonyl allylation with chromium complex, we recently reported enantioselective chromium catalyzed carbonyl 2-(alkoxycarbonyl)allylation leading to synthetic useful α-exo-methylene-γ-butyrolactones[20], dearomative coupling of halomethylheteroarenes[20, 21], chiral quaternary stereogenic centers formation[22]
Chiral β-hydroxy allylsilanes and derivatives have been extensively used by Roush, Panek and others for the synthesis of 1,2- and 1,4-diols in the total synthesis of natural products[26,27,28,29,30,31,32]
Summary
Carbonyl allylation with functionalized allyl reagents has been a sustained research topic, as in this transformation, two new functionalities including one alcohol and a terminal C-C double bond are generated[1]. We first tested the reaction in the absence of any chiral ligands, to our delight, the desired homoallylic alcohol was generated in good yield as a single diastereomer (Fig. 2, entry 2).
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