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Claisen rearrangements of benzyl vinyl ethers: theoretical investigation of mechanism, substituent effects, and regioselectivity

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Abstract

Recently we reported the aromatic Claisen rearrangements of benzyl ketene acetals, which form one of the few examples of aromatic Claisen rearrangements involving benzyl vinyl ethers (as opposed to allyl aryl ethers, which are the usual substrates for aromatic Claisen rearrangements). Theoretical calculations predict that these rearrangements proceed via a concerted [3,3]-sigmatropic transition state, which is similar in geometry to the TS for the Claisen rearrangement of an allyl aryl ether but has a 4 kcal mol−1 higher barrier. The effects of donor (OMe) and acceptor (CN) substituents on the kinetics of the [3,3]-rearrangement mirror those reported for allyl vinyl ethers: the largest substituent effects are seen for 1-OMe, 2-OMe, 2-CN, and 4-CN substituents, which lower the barrier by 5–9 kcal mol−1. Substituents on the aromatic ring have smaller effects on the barrier (≤2 kcal mol−1). The regioselectivities of Claisen rearrangements of meta-substituted benzyl ketene acetals favour 1,2,3-trisubstituted products in preference to the less sterically congested 1,2,4-isomers due to favourable orbital interactions in the 1,2,3 transition state.

Graphical abstract: Claisen rearrangements of benzyl vinyl ethers: theoretical investigation of mechanism, substituent effects, and regioselectivity

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Publication details

The article was received on 07 Jul 2017, accepted on 01 Sep 2017 and first published on 11 Sep 2017


Article type: Paper
DOI: 10.1039/C7OB01666B
Citation: Org. Biomol. Chem., 2017, Advance Article
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    Claisen rearrangements of benzyl vinyl ethers: theoretical investigation of mechanism, substituent effects, and regioselectivity

    E. H. Krenske, J. M. Burns and R. P. McGeary, Org. Biomol. Chem., 2017, Advance Article , DOI: 10.1039/C7OB01666B

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