Synthesis of tri-substituted biaryl based trianglimines: formation of C-3-symmetrical and non-symmetrical regioisomers

2-Functionalised aromatic monoaldehydes were synthesised in good to excellent yields by reacting 4-bromo-2-fluorobenzaldehyde with different secondary amines and phenol. The Suzuki-coupling reaction of the newly functionalised aromatic monoaldehydes with 4-formylphenylboronic acid afforded the corresponding 2-functionalised-4,4'-biphenyldialdehydes in good yields (47-85%). The [3+3]-cyclocondensation reactions of the 2-functionalised-4,4'-biphenyldialdehydes with (1R,2R)-1,2-diaminocyclohexane afforded a mixture of regioisomeric C-3-symmetrical and non-symmetrical trianglimines. Reduction of the C-3-symmetrical and the non-symmetrical trianglimines with NaBH4 in a mixture of THF and MeOH afforded the corresponding trianglamines in high yields.