One‐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.
Abstract. Nine heterocyclic zwitterionic boronate esters derived from carbonylphenylboronic acids and amino-diols are described. Compounds were prepared by direct condensation reaction between 3- or 4-formyl/acetylphenylboronic acids with 2-amino-2-methyl-1,3-propanediol (1a-1d) or serinol (2-amino-1,3-propanediol) (1e-1h). Compound 2e was obtained by reaction between 4-formylphenylboronic acid and serinol using a solvent mixture methanol/acetone, an aldol condensation reaction was observed. All compounds were characterized by common spectroscopic techniques such as FT-IR, mass spectrometry, and multinuclear 1H, 13C and 11B NMR spectroscopy. 11B NMR spectra showed signals between δ = 1.9 to 7.3 ppm for all compounds, indicating a tetracoordinated environment for the boron atoms in solution. X-ray diffraction analysis showed that boronates are contained in six-membered heterocycles, which have a chair conformation with -OH and -NH3+ substituents in syn disposition. The formation of channels in the crystal lattice that are filled with water and supported by hydrogen bonding interactions is noteworthy.
Resumen. En el presente trabajo se describen nueve ésteres de boro zwitteriónicos, derivados de ácidos cabonilfenilborónicos. Los compuestos fueron obtenidos mediante reacciones de condensación entre el ácido 3- o 4- formil/acetilfenilborónico con 2-amino-2-metil propanodiol (1a-1d) o serinol (1e-1h). El compuesto 2e se sintetizó a través del ácido 4-formilfenilborónico y serinol (2-amino-1,3-propanodiol) utilizando una mezcla de disolventes metanol/acetona, dando lugar a una reacción de condensación aldólica. Los compuestos fueron caracterizados por técnicas espectroscópicas como son FT-IR, espectrometría de masas y espectroscopia multinuclear de RMN 1H, 13C y 11B. El espectro RMN de 11B mostró señales anchas entre δ = 1.9 y 7.3 ppm para todos los compuestos, lo cual indica la presencia de átomos de boro tetracoordinados en solución. El análisis por difracción de rayos-X de monocristal mostró la formación de heterociclos de 6 miembros en conformación silla, con una marcada estereoselectividad en donde los grupos -OH y -NH3+ se encuentran en disposición syn. En la red cristalina, se observaron canales ocupados por moléculas de agua y soportados por enlaces de hidrógeno.
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