Synthesis of functionalized diarylborinic 8-oxyquinolates via bimetallic boron–lithium intermediates

The simple one-pot approach to functionalized diarylborinic 8-oxyquinolates has been developed starting with selected dihalobenzenes (Hal = Br, I) and (dialkoxy)phenylboranes PhB(OR)2 (R = Me, Et). The initial step results in halogenated diarylborinic “ate” complexes which are prone to halogen–lithium exchange when treated with t-BuLi. The resultant dianionic lithiated diarylborinic “ate” complexes of the type [(LiAr)PhB(OR)2]Li were reacted with selected electrophiles followed by hydrolysis to give unsymmetrically substituted diarylborinic acids isolated in the form of respective 8-hydroxyquinoline complexes as the final products in moderate to good yields. The crystal structure of (2-fluoro-4-formylphenyl)(phenyl)borinic 8-oxyquinolinate has been determined by X-ray diffraction. The alternative method involving the lithiation of B-protected bis(halophenyl)borinic N,N-dimethylethanolamine esters followed by the quench with electrophiles has also been investigated.