Chelation-assisted nucleophilic aromatic substitution of 2-sulfonyl-substituted 1-methoxynaphthalenes by Grignard reagents: Factors determining the activating ability of the 2-sulfonyl substituents

1-Methoxynaphthalenes 3-7 having sulfonyl substituents SO₂R (R = Me, Prⁱ, Bu^t, OPh and N[CH₂]₃CH₂) at the 2-position undergo displacement of the 1-methoxy group on treatment with the Grignard reagents 8a-d by a chelation-assisted conjugate addition-elimination process. Activating ability of these sulfonyl groups for the apparent nucleophilic aromatic substitution is compared with that of an ester group, isopropoxycarbonyl, and a sulfinyl group, tert-butylsulfinyl, and found to fall roughly in the order CO₂Prⁱ > SO₂OPh > SO₂N[CH₂]₃CH₂ ≥ SO₂Alkyl ≫ SOBu^t. The activation order is interpreted as being the outcome of a balance between the electron-withdrawing strength of the 2-substituents and the steric hindrance caused by the Grignard reagents 8a-d on approach to the substrates 1-methoxynaphthalenes 1-7. Asymmetric binaphthyl coupling by reaction of the chiral sulfamoyl-substituted naphthalene 20 with 1-naphthyl Grignard reagents 8d,e is also reported.