Four-component assembly of chiral N-B heterocycles with a natural product-like framework

Stereoselective formation of boron-stereogenic organoboron derivatives

Four-coordinate organoboron derivatives present interesting chemical, physical, biological, electronical, and optical properties. Given the increasing demand for the synthesis of smart functional materials based on chiral organoboron compounds, the exploration of stereoselective synthesis of boron-stereogenic organo-derivatives is highly desirable. However, the stereoselective construction of organoboron compounds stereogenic at boron has been far less studied than other elements of the main group due to configurational stability concerns. Nowadays, these species are no longer elusive and configurationally stable compounds have been highlighted. The idea is to show the potential of the stereoselective building of the four-coordinate boron centre and encourage future endeavors and developments in the field.

Multicomponent Synthesis of Luminescent Iminoboronates

A family of iminoboronates was prepared through a one-pot multicomponent reaction, starting from boronic acid, anthranilic acid, and different salicylaldehydes. Their synthesis was straightforward and the complexes were obtained in good to excellent yields. Their photophysical properties were assessed in a diluted solution, and the complexes proved to be faintly luminescent. These chelates demonstrated remarkable Aggregation-Induced Emission Enhancement, which was rationalized using crystal structures.

Reactivity and Synthetic Applications of Multicomponent Petasis Reactions

The Petasis boron-Mannich reaction, simply referred to as the Petasis reaction, is a powerful multicomponent coupling reaction of a boronic acid, an amine, and a carbonyl derivative. Highly functionalized amines with multiple stereogenic centers can be efficiently accessed via the Petasis reaction with high levels of both diastereoselectivity and enantioselectivity. By drawing attention to examples reported in the past 8 years, this Review demonstrates the breadth of the reactivity and synthetic applications of Petasis reactions in several frontiers: the expansion of the substrate scope in the classic three-component process; nonclassic Petasis reactions with additional components; Petasis-type reactions with noncanonical substrates, mechanism, and products; new asymmetric versions assisted by chiral catalysts; combinations with a secondary or tertiary transformation in a cascade- or sequence-specific manner to access structurally complex, natural-product-like heterocycles; and the synthesis of polyhydroxy alkaloids and biologically interesting molecules.

Petasis three-component reactions for the synthesis of diverse heterocyclic scaffolds

The Petasis three-component reaction (PR) of hydroxy aldehydes, amines and boronic acids is an important multi-component reaction for the synthesis of structurally diverse scaffolds and biologically interesting small molecules. The reaction has been significantly explored in the past decade, and many new variants have emerged, such as asymmetric, traceless and four-component approaches. The excellent stereoselectivity, high yield and broad functional group tolerance altogether make this reaction ideal for fragment and compound collection synthesis, since orthogonal chemical handles can be incorporated for subsequent scaffold formation and appendage modification. Herein we present a selection of recent variations on the PR theme for the synthesis of scaffolds of relevance to medicinal chemistry.

Base catalysed N-functionalisation of boroxazolidones

A method for the condensation of boroxazolidones derived froml-valine with aromatic aldehydes, catalysed by 1,5,7-triazabicyclo[4.4.0]dec-5-ene was developed.

A Three-Component Assembly Promoted by Boronic Acids Delivers a Modular Fluorophore Platform (BASHY Dyes)

The modular assembly of boronic acids with Schiff-base ligands enabled the construction of innovative fluorescent dyes [boronic acid salicylidenehydrazone (BASHY)] with suitable structural and photophysical properties for live cell bioimaging applications. This reaction enabled the straightforward synthesis (yields up to 99%) of structurally diverse and photostable dyes that exhibit a polarity-sensitive green-to-yellow emission with high quantum yields of up to 0.6 in nonpolar environments. These dyes displayed a high brightness (up to 54,000 M(-1) cm(-1)). The promising structural and fluorescence properties of BASHY dyes fostered the preparation of non-cytotoxic, stable, and highly fluorescent poly(lactide-co-glycolide) nanoparticles that were effectively internalized by dendritic cells. The dyes were also shown to selectively stain lipid droplets in HeLa cells, without inducing any appreciable cytotoxicity or competing plasma membrane labeling; this confirmed their potential as fluorescent stains.

A Four-Component Reaction for the Synthesis of Dioxadiazaborocines

A four-component reaction for the synthesis of heterocyclic boronates is reported. Readily available hydrazides, α-hydroxy aldehydes, and two orthogonally reactive boronic acids are combined in a single step to give structurally distinct bicyclic boronates, termed dioxadiazaborocines (DODA borocines). In this remarkable process, one boronic acid reacts as a carbon nucleophile and the other as a boron electrophile to provide enantio- and diastereomerically pure heterocyclic boronates with multiple stereocenters in high yields.

Discovery of new heterocycles with activity against human neutrophile elastase based on a boron promoted one-pot assembly reaction

Herein we demonstrate for the first time that a boron promoted one-pot assembly reaction may be used to discover novel enzyme inhibitors. Inhibitors for HNE were simply assembled in excellent yields, high diastereoselectivities and IC50 up to 1.10 μM, based on components like salicylaldehyde, aryl boronic acids and amino acids. The combination of synthetic, biochemical, analytical and theoretical studies allowed the identification of the 4-methoxy or the 4-diethyl amino substituent of the salicylaldehyde as the most important recognition moiety and the imine alkylation, lactone ring opening as key events in the mechanism of inhibition.

Facile synthesis of highly fluorescent BF2 complexes bearing isoindolin-1-one ligand

A new class of isoindolin-1-one based BF₂ complexes containing pyridine or benzothiazole groups has been prepared from a “one-pot” reaction.

Syntheses and photophysical properties of BF2 complexes of curcumin analogues

Highly photostable π-extended curcumin-BF₂ complexes with strong absorption and fluorescence ranging from 400 to 800 nm were reported.

Phenylalanine iminoboronates as new phenylalanine hydroxylase modulators

Herein we report the discovery of new modulators of human phenylalanine hydroxylase (hPAH) inspired by the structure of its substrate and regulator l-phenylalanine.

Study of boron-nitrogen dative bonds using azetidine inversion dynamics

A method for probing the strength of B-N dative bonds is reported. The activation parameters for nitrogen inversion in a series of azetidines tethered to boronate esters have been quantified by VT-NMR and the measured barriers correlated with data obtained by (11)B NMR, X-ray crystallography and MP2 calculations.

One-pot tandem cyclization of enantiopure asymmetric cis-2,5-disubstituted pyrrolidines: Facile access to chiral 10-heteroazatriquinanes

A series of chiral 10-heteroazatriquinanes were synthesized from enantiopure asymmetric cis-2,5-disubstituted pyrrolidines through a one-pot tandem cyclization procedure. The structures and configurations of these new chiral 10-heteroazatriquinanes are confirmed by X-ray single-crystal diffraction analysis.