Carbon–hydrogen and C–X (X = Cl or SiMe3) bond activation. 1-Cyclopalladation and oxidation of some derivatives of 2-[(dimethylamino)methyl]naphthalene

Abstract

The regioselective palladation reactions of 3-substituted derivatives of 2-[(dimethylamino)methyl]naphthalene, C₁₀H₆(CH₂NMe₂)-2-R-3 (R = Cl, SiMe₃ or OSiMe₃), were studied. For the substrate with R = Cl, no cyclopalladation at position 1 was observed and the co-ordination complex was isolated. The 3-palladated product was formed in 10% yield via C–Cl activation. The reaction of 2-[(dimethylamino)methyl]-3-methylnaphthalene with Pd(O₂CMe)₂ and work-up with LiCl did lead to palladation at position 1, the resulting complex being isolated in 96% yield. The crystal structure of bis(acetonitrile){2-[(dimethylamino)methyl]-3-methyl-1-naphthyl}palladium trifluoromethanesulfonate was solved. Monoclinic, space group P2₁/n, with a= 13.193(1), b= 11.801(1), c= 14.797(1)Å, β= 105.15(1)°, Z= 4. The structure was refined to R= 0.042 for 3455 reflections with I > 2.5σ(I). Palladation at position 1 was also achieved by oxidative addition of 1-bromo-2-[(dimethylamino)methyl]naphthalene to [Pd(dba)₂](dba = dibenzylideneacetone). Protection of C(3) with R = SiMe₃ resulted in quantitative replacement of the SiMe₃ group by palladium. Silicon–oxygen bond cleavage was observed when the substrate with R = OSiMe₃ was treated with Pd(O₂CMe)₂. Palladium bis{3-[(dimethylamino)methyl]-2-naphtholate} was obtained quantitatively. Oxidation of several arylpalladium complexes with Bu^tO₂H was achieved in the presence of [VO(acac)₂](acac = acetylacetonate) or [{RhCl(cod)}₂]}(cod = cycloocta-1,5-diene) as catalyst. The corresponding 1-naphthols were prepared in yields varying from 33 to 78%. In a number of cases the corresponding 1,4-naphthoquinones were prepared in yields varying from 18 to 38%.