Studies of diastereoselectivity in conjugate addition of organoaluminum reagents to (R)-[(p-tolylsulfinyl)methyl] quinols and derivatives

(R)-4-Hydroxy-4-[(p-tolylsulfinyl)methyl]-2,5-cyclohexadienones 1-3, and 6 reacted with organoaluminum derivatives from the pro-R conjugated position in a highly pi-facial diastereoselective manner directed by the C-4 OH. A similar facial diastereoselectivity arose from reactions with 3-alkyl-substituted analogues 4 and 5 and 5-alkyl-4-hydroxy-4-[(p-tolylsulfinyl)methyl]-2-cyclohexenones 10a,b. Semiempirical calculations (AM1 model) provide data on transition-state energies for additions in full agreement with the experimental results.