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Issue 32, 2018
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Base-promoted diastereoselective α-alkylation of borane N-((S)-1′-phenylethyl)azetidine-2-carboxylic acid ester complexes

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Abstract

The base-promoted α-alkylation of N-((S)-1-phenylethyl)azetidine-2-carboxylic acid esters 1 was investigated. The use of diastereomerically pure borane complexes 3 as substrates, which are easily prepared from 1, dramatically improved the yields and diastereoselectivities of α-alkylated products 2. For example, the treatment of tert-butyl ester (1S,2S,1′S)-3a with 2.4 equivalents of lithium bis(trimethysilyl)amide (LiHMDS) at 0 °C followed by 2.6 equivalents of benzyl bromide afforded α-benzylated (2S,1′S)-2aa in 90% yield as almost a single diastereomer. Our method enables the production of optically active α-substituted azetidine-2-carboxylic acid esters starting from commercially available (S)-1-phenylethylamine, which is one of the least expensive chiral compounds.

Graphical abstract: Base-promoted diastereoselective α-alkylation of borane N-((S)-1′-phenylethyl)azetidine-2-carboxylic acid ester complexes

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Publication details

The article was received on 12 Jun 2018, accepted on 26 Jul 2018 and first published on 27 Jul 2018


Article type: Paper
DOI: 10.1039/C8OB01395K
Citation: Org. Biomol. Chem., 2018,16, 5833-5845
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    Base-promoted diastereoselective α-alkylation of borane N-((S)-1′-phenylethyl)azetidine-2-carboxylic acid ester complexes

    E. Tayama, R. Nishio and Y. Kobayashi, Org. Biomol. Chem., 2018, 16, 5833
    DOI: 10.1039/C8OB01395K

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