1,4-Addition of Lithium Organyls to para-Quinols / Structure Determination of 2,6-Di-tert-butyl-4-hydroxy-4,5-diphenylcyclohex-2-en-1-one

Abstract

Addition of lithium organyls to sterically hindered para-quinols leads to 1,2-or 1,4-adducts. The 1,4-addition prevails, if the 4-substituents in the quinol and the organic group in the lithium organyl are large. Four 1,4-addition products (2-cyclohex-2-en-l-ones) are synthesized and their structures investigated by NMR spectroscopy. The aryl groups at C-4 and C-5 acquire equatorial positions, the alkyl group at C-6 is bisectional. These results are confirmed by Xray analysis of 2,6-di-terr-butyl-4-hydroxy-4,5-diphenylcyclohex-2-en-1 -one, revealing a twist boat conformation of the cyclohexene ring.

Studies of Diastereoselectivity in Conjugate Addition of Organoaluminum Reagents to (R)-[(p-Tolylsulfinyl)methyl]quinols and Derivatives

“…The high π-facial diastereoselectivity directed by the OH could be expected considering the similar diastereoselective 1,4-addition found in Grignard reactions on lithium alkoxides of p -quinols 8a in racemic series. Moreover, we could assume an essential role of the free OH in directing the reaction to the conjugate position since the reaction of different organometallic species with p -quinol derivatives having no free OH proceeded through stereoselective 1,2-addition. ,, Even more remarkable was the effective diastereotopic CC bond selection observed when prochiral cyclohexadienones were present, since to our knowledge, the dienone desymmetrization of an optically active p -quinol had only been achieved in an intramolecular conjugate addition …”