1683-98-3Relevant academic research and scientific papers
Stereochemistry of LiNR2-Induced 1,4-Elimination of Allylic (benzylic) Ethers
Moss, Randall J.,Rickborn, Bruce
, p. 1992 - 1996 (1986)
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.
Hydrogen Transfer Reactions, 10. The cis-Selective Two-Step Mechanism in Hydrogen Transfer from 1,4-Dihydroarenes to o- and p-Quinones
Brock, Martin,Hintze, Horst,Heesing, Albert
, p. 3727 - 3736 (2007/10/02)
Deuterium labeling experiments prove a high cis selectivity for hydrogen transfer reactions between 1,4-dihydroarenes and o- and p-quinones.Solvent effects and the size of primary isotope effects exclude a symmetry-allowed synchronous transfer of both hydrogens.They are consistent with a primary hydride abstraction to form a sterically fixed ion pair.The cis selectivity is raised by the larger ? system of 2 and reduced in the case of polar solvents.Tunneling of hydrogen is indicated by large primary isotope effects.
