ipso-and para-Functionalization of meta-terphenyl ligands with substituted methyl groups: Unusual head-to-tail coupling of terphenyl moieties

The synthesis and characterization of several ipso -functionalized derivatives of the bulky terphenyl group View the MathML sourceC6H3-2,6(C6H3-2′,6′-Pr2i)2(Ar′) are described. These include the primary alcohol Ar′CH2OH (1), the bromo derivative Ar′CH2Br (2), and the terphenyl formate Ar′CH2OC(O)H (3). The alcohol 1 was obtained by treatment of LiAr′ with formaldehyde, and 1 was readily converted to the bromo derivative 2 using HBr. The reaction of 1 with formic acid afforded 3 in good yield. Attempts to form the Grignard derivative of 1, i.e., Ar′CH2MgBr, resulted in a head-to-tail reaction of the terphenyl benzyl units to yield an unusual coupled product 4. An approach to the avoidance of this coupling involved the synthesis of the terphenyl derivatives View the MathML source1-I-C6H2-2,6(C6H3-2′,6′-Pr2i)2-4-Me(5) and View the MathML source1-I-C6H2-2,6(C6H2-2′,4′,6′-Pr3i)2-4-Me(6), bearing methyl groups in the para positions of the central aryl ring, which could be prepared in good yield, and converted to their respective lithium salts 7 and 8 without complication . The compounds were characterized by 1H and 13C NMR spectroscopy, IR spectroscopy (1) and X-ray crystallography (2, 4, 5 and 6).