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.