Bis‐Imine Boronic Esters Obtained by One‐Step Multicomponent Reactions. Synthesis and X‐Ray Diffraction Structural Analysis

Abstract

AbstractOne‐step multicomponent reactions were used for the synthesis of bis‐imine boronic esters (1 a–1 c and 2 a–2 c). Condensation reaction between benzene‐1,4‐diboronic acid, 2‐amino‐1,3‐diols (2‐amino‐1,3‐propanediol or 2‐amino‐2‐methyl‐1,3‐propanediol) and carboxyl‐ pyridines (2‐, 3‐ or 4‐pyridinecarboxaldehyde) offers stable boronic esters in good yields. X‐ray crystal analysis was done for all six compounds showing at supramolecular level the presence of numerous secondary interactions such as, C−H⋅⋅⋅O, C−H⋅⋅⋅N, C−H⋅⋅⋅ π hydrogen bonds and π⋅⋅⋅π stacking. The existence of these interactions gives place to 1D and 2D polymeric frameworks in solid state. It is noteworthy to remark the absence of the N→B coordination bond in either solution or solid state. All 2‐amino‐1,3‐propanediol derivatives (1 a–1 c) showed to be in a linear conformation while the 2‐amino‐2‐methyl‐1,3‐propanediol derivatives (2 a–2 c) were twisted to form a zig‐zag conformation. Additionally, 1 b was co‐crystallized with benzene‐1,4‐diboronic acid (1 b–Ac) and 2 a also was crystallized as solvate with toluene included at the unit cell (2 a–Tol). The X‐ray analysis reveals that the additional molecule (diboronic acid or toluene) not alter the whole conformation.