Reaction of p-tert-butylcalix[4] arene with dichlorodimethylsilane and subsequent alkylation. A disproportionation reaction?

Treatment of p-tert-butylcalix[4]arene with dichlorodimethylsilane yields a single product, p-tert-butylcalix[4]areneSiMe(2)(OH)(2) (4), in which one dimethylsilyl group bridges adjacent oxygens. Subsequent treatment of 4 with butyllithium and methyl trifluoromethanesulfonate yields two products, p-tert-butylcalix[4]arene(SiMe(2))(2) (5) and a lithium triflate complex of p-tert-butylcalix[4]arene(OMe)(4), 6 . LiO3SCF3. No evidence is found for the expected product p-tert-butylcalix[4]areneSiMe(2)(OMe)(2) (7). This can be viewed as a formal disproportionation reaction of 7, although the mechanism of the formation of 5 and 6 likely does not involve initial formation of 7. A large difference in the H-1 NMR resonances for the nonequivalent methylsilyl groups in both 4 and 5 is found. This is attributed to the proximity of one methyl group to the pi system of the aromatic rings of the calix[4]arene backbone. The structures of 4 and 5 were determined by X-ray diffraction.