Novel Grignard reaction of chelated boric esters derived from diethyl (2R,3R)-tartrate: a one-step access to a bulky γ,γ,γ-trisubstituted γ-hydroxy-β-ketoester via selective arylation and sequent deboronation

Reaction of the tetracoordinated spiroborate esters derived from diethyl (2R,3R)-tartrate with Grignard reagents was further examined and found that sterically hindered MesMgBr has different reaction behavior from PhMgBr to the spiroborate esters. It has been proved that in the case of PhMgBr reaction, the formation of the chiral bicyclodiboronic ester (R,R)-2 was accomplished step by step via two 1,3-cyclizations of the hydrolytic products of the resulting boron compound. However, in the case of MesMgBr reaction, only one esteral group of the tartrate moiety was diarylated, and a bulky γ,γ,γ-trisubstituted γ-hydroxy-β-ketoester and mesitylboronic anhydride were provided after the resultant was worked up. The composition and structure of the products were authorized by the spectral and single crystal X-ray analysis. A formation mechanism of γ-hydroxy-β-ketoester and mesitylboronic anhydride was also suggested.