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. 2009 Feb 5;11(3):511-3.
doi: 10.1021/ol802289f.

Si-based benzylic 1,4-rearrangement/cyclization reaction

Barry M Trost  1 , Andreas Bertogg
Affiliations

Si-based benzylic 1,4-rearrangement/cyclization reaction

Barry M Trost et al. Org Lett. .

Abstract

The trans-selective hydrosilylation of ynones (1) yields beta-silylated enones (2) that undergo a benzylic 1,4-rearrangement/cyclization reaction in the presence of base, yielding 2,5-dihydro-1,2-oxasiloles (3).

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Figures

Scheme 1
Scheme 1
A Si-based benzylic 1,2-shift.
Figure 1
Figure 1
Discovery of the benzylic 1,4-shift.
Scheme 2
Scheme 2
Further proof for structure. Use of the rearrangement as an alternative access to the aldol structural motif.
Figure 2
Figure 2
Benzylic 1,4-shift vs. 1,2-shift: a mechanistic proposal.
None
See this image and copyright information in PMC

References

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    1. A 1,4-shift of allyl or crotyl substituents from Si to carbonyl C under thermal conditions was reported recently. See: Bashiardes G, Chaussebourg V, Laverdan G, Pornet J. Chem. Commun. 2004:122–123.. An interesting allylic 1,4-rearrangement as part of a two-step process including a Rh-catalyzed silylformylation (notably, in this transformation no silacycle is isolated) was described. See: O'Malley SJ, Leighton JL. Angew. Chem. Int. Ed. 2001;40:2915–1917.. Applying thermal conditions (such as described by Bashiardes et al.) to the γ-silylated enones used in this study did not result in a rearrangement.

    1. The structural assignment for the 2,5-dihydro-1,2-oxasiloles products by NMR experiments was verified based on two-dimensional NMR measurements for 3b.

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