REACTIVITE DE LITHIENS DERIVES D'ETHERS DE LA CYANHYDRINE DU BENZALDEHYDE VIS-A-VIS D'α-ENONES CYCLIQUES

Article abstract of DOI:10.1016/0040-4020(84)85069-3

Conjugate addition of reagent 1A to 2-cyclohexenone 3 can be realized in THF-HMPT, so that one-pot conjugate addition - CH3I enolate trapping, leading to trans 2-methyl 3-benzoylcyclohexanone 17 can be easily performed.From isophorone 4 and Δ¹⁽⁹⁾-2-octalone 5, 1,4-addition under kinetic control is observed in THF.In the presence of HMPA, the reaction is under thermodynamic control.At low temperatures enolate 19a is in equilibrium with 1A and 4; from 4 at 0 deg C or 5 at -65 deg C or at 0 deg C, the equilibrium lies on the side of starting materials.No reaction between 1A and 6 takes place in any solvent.The reaction of 1B and isophorone 4 in THF leads to 1,2-addition under kinetic control and to 1,4-addition under thermodynamic control.In THF-HMPT, retro-Michael addition is observed.However, 1,2-addition takes place in THF to 6. The different results are interpreted in terms of interplay of ion-pairing, steric decompression and steric hindrance to 1,4-addition as well as the possibility of participation of the Li cation for 1,2-addition.