Synthesis and structure of benzoboroxoles: novel organoboron heterocycles

1,3‐Dihydro‐1‐hydroxy‐3‐morpholin‐4‐yl‐2,1‐benzoxaborole: product of the reaction of o‐formylphenylboronic acid with morpholine

“…The crystal structure of the title compound ( Fig. 1) consists of the hydrogen-bonded dimer motif, which is very similar to that observed in two other benzoxaborole derivatives, namely 1-hydroxy-1,3-dihydro-2,1-benzoxaborole 9 and its 5,7-dimethoxy derivative. 10 In all cases the dimer is centrosymmetric and the interactions are relatively strong, with O· · ·O distances of 2.75-2.80Å.…”

“…For instance, the C-B bond varies over 0.4Å in two independent molecules of 1-hydroxy-1,3-dihydro-2,1-benzoxaborole. 9 Unfortunately, the lack of structural characterization of other benzoxaborole derivatives precludes a systematic study of this point. Systematic work on the synthesis and characterization of the products of reactions with other amines is in progress.…”

A diverse structural behaviour of boronated ortho-phthalaldehydes: A crystal structure of 1,3-dihydro-1,3-dihydroxy-4-formylbenzo[c][2,1]oxaborole

“…1. The metric features of the molecule 2-II (Table 1) are similar to those reported for related 1,3-dihydro-1-hydroxybenzo [c][2,1]oxaborole [11], and its derivatives [12]. The 3-formyl group is nearly coplanar with the aromatic ring while the C@O bond adopts the exo-orientation with respect to the adjacent boraheterocycle.…”

“…Comparison of signal integration gives a cyclic to acyclic tautomer ratio of 12 at 293 K. Unlike 2, the isomeric compound 4 exists in one typical acyclic form as evidenced by two formyl hydrogen resonances at 10.50 and 10.45 in the 1 H NMR spectrum, and corresponding signals of formyl carbons at 193.9 and 193.6 ppm in the 13 C NMR spectrum. Moreover, a comparison of 11 Fig. 17 in the Supplementary Material).…”

“…5%) was detected by 1 H NMR analysis in [D 6 ] acetone. Other intramolecular cyclizations leading to benzo [c][2,1]oxaboroles are more entropy-favoured due to elimination of water molecule [10,11].…”