First Unambiguous Characterization of a Novel RO-BH₂Intermediate by¹H{¹¹B} and¹H{¹³C,¹¹B} NMR Spectroscopy. Proof of Boron−Carbonyl Interaction through Innovative Use of NMR Techniques

An unusual reduction of the aryl-substituted 3-hydroxyacrylic acid ester 1 by BH3 results in the propenoic acid ethyl ester 3. We were able to prove the presence of an intermediate 2 containing a cyclic O-BH2 <- O=C< moiety in 2 by using H-1-B-11 and H-1- C-13{B-11} NMR correlation experiments.