Synthesis, structures and catalytic activity of some BINOL based boronates and boronium salts

Abstract

The BINOL supported chiral boronate ester [C₁₀H₁₂O₂BC₆F₅(THF)] [(R)-1], [C₁₀H₁₂O₂BC₆F₅(OPEt₃)] [(R)-3] and [C₁₀H₁₂O₂BC₆F₅]₂ [(R,R)-2] as well as the chiral boronium salts [C₁₀H₁₂O₂B(OPEt₃)₂]⁺[B(O₂C₁₀H₁₂)₂]⁻, [(R)-6] and [C₁₀H₁₂O₂B(OSMe₂)₂]⁺[B(O₂C₁₀H₁₂)₂]⁻ [(R)-7] have been synthesized, characterized by NMR spectroscopy, and the solid state structures of [(R)-1], [(R,R)-2] and [(R)-3] determined. Chiral ester [(R)-1] was found to be a potent Lewis acid, similar to B(C₆F₅)₃, and capable of rapidly catalyzing the annulation of (R)-, (S)- and rac-styrene oxide with nitrone PhCHN(O)Me to trans-2-methyl-3,6-diphenyl-1,4,2-dioxazine (trans-11) with high regio- and diastereoslectivities.