Stereochemistry of LiNR2-Induced 1,4-Elimination of Allylic (benzylic) Ethers

Article abstract of DOI:10.1021/jo00361a011

The stereochemistry of base-induced 1,4-elimination of H,D-substituted allylic (benzylic) ethers is examined.The substrates used are structurally similar (cyclohexenyl systems) but differ significantly in the nature of the "diene" product which is generated, forming naphthalene in one case and a very reactive intermediate o-xylylene in the other.These differences are reflected in the ease of elimination, allowing in the naphthalene-forming system examination of a range of bases/conditions.Preferential syn elimination, ranging from 87percent to <*>99percent, depending upon the solvent, substrate, and base employed, is found.An H/D kinetic isotope effect of approximately 3.4 is observed for the LDA-induced reaction in hexane; in spite of this, syn elimination of cis-deuterated substrate is strongly preferred, with no detectable diminution of selectivity under these conditions.Very high syn selectivity is found for reaction of potassium tert-butoxide and also when a quaternary ammonium hydroxide is employed, showing that, although lithium coordination may be important for LiNR2-induced elimination, other factors must contribute to this stereochemical course.The substrate which generates an o-xylylene intermediate also does so with very high syn selectivity.Conformational effects may dictate the syn preference of these and related cyclohexenyl systems.

Full text of DOI:10.1021/jo00361a011

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Evaluation Only. Created with Aspose.PDF. Copyright 2002-2021 Aspose Pty Ltd.

Evaluation Only. Created with Aspose.PDF. Copyright 2002-2021 Aspose Pty Ltd.

Evaluation Only. Created with Aspose.PDF. Copyright 2002-2021 Aspose Pty Ltd.