Synthesis of Aminoboronic Acid Derivatives from Amines and Amphoteric Boryl Carbonyl Compounds

A Boron Scan of Ethyl Acetoacetate Leads to Versatile Building Blocks

Discovered in the 19th century, ethyl acetoacetate has been central to the development of organic chemistry, including its pedagogy and applications. In this study, we present borylated derivatives of this venerable molecule. A boron handle has been installed at either α ${{\rm \alpha }}$ - or β ${\beta }$ -position of acetoacetate by homologation of acyl-MIDA (N-methyliminodiacetic acid) boronates with diazoacetates. Either alkyl or boryl groups were found to migrate with regiochemistry being a function of the steric bulk of the diazo species. Boryl β ${{\rm \beta }}$ -ketoesters can be further modified into borylated pyrazolones and oximes, thereby expanding the synthetic toolkit and offering opportunities for additional modifications.

Synthesis of Fluorinated Aminoalkylboronic Acids from Amphoteric α-Boryl Aldehydes

Our ongoing search for underdeveloped functional group combinations has brought to light α-fluorinated aminoalkylboronic acids, a new class of molecules featuring the B-CF linkage. These compounds can now be generated from secondary amines and α-boryl aldehydes through electrophilic fluorination of boryl enamines or enamides. Fluorinated β-aminoalkylboronic acids show no signs of degradation under ambient conditions. We present evidence for the involvement of chair-like motifs, favored over the acyclic forms by up to 1.7±0.1 kcal mol^-1 in water and held together by an amine-boronate hydrogen bond. Fluorinated β-aminoalkylboronic acids are stable over a wide pH range and are characterized by a pK_a of 3.4, which is the lowest of any alkylboronic acid.

Formyl MIDA Boronate: C1 Building Block Enables Straightforward Access to α-Functionalized Organoboron Derivatives

Formyl MIDA boronate has been known to be an elusive type of acylboronate that has not been obtained to date. In this work, an approach to the one-pot preparation and chemical transformations of formyl MIDA boronate were developed to provide new types of α-functionalized organoboron compounds. Among them are acylboronate reagents which present boron-substituted analogues of ynones and β-dicarbonyl compounds. The developed synthetic procedures, utilizing formyl MIDA boronate, are tolerant to diverse functional groups, making this reagent an advantageous C₁ building block for extending the scope of organoboron chemistry.

Synthesis and Tunable Optical Properties of C,N-Chelated Borate Luminophores Derived from Potassium Acyltrifluoroborates

A new class of borate luminophores has been synthesized by a simple two-step reaction using potassium acyltrifluoroborates (KATs) as starting materials. The hydrazones obtained from reactions between KATs and 2-hydrazinopyridines followed by a cyclization resulted in the unprecedented formation of C,N-chelated six-membered bora-heterocycles. Under consideration of the results of DFT and TD-DFT calculations, four luminophores based on such bora-heterocycles are designed and synthesized, which exhibit a tunable fluorescence range from blue to red in the solid state. Moreover, one of the luminophores exhibits mechanofluorochromism from blue to yellow/green. As a result of the aforementioned mechanochromism of one of these luminophores, white-color emission was achieved by simply mixing the four luminophores.

Diversity-Oriented Synthesis of α-Functionalized Acylborons and Borylated Heteroarenes by Nucleophilic Ring Opening of α-Chloroepoxyboronates

The ring-opening reactions of N-methyliminodiacetyl (MIDA) α-chloroepoxyboronates with different nucleophiles allow the modular synthesis of a diverse array of organoboronates. These include seven types of α-functionalized acylboronates and seven types of borylated heteroarenes, some of which are difficult-to-access products using alternative methods. The common synthons, α-chloroepoxyboronates, could be viably synthesized by a two-step procedure from the corresponding alkenyl MIDA boronates. Mild reaction conditions, good functional-group tolerance, and generally good efficiency were observed. The utility of the products was also demonstrated.

Concise Synthesis of Potassium Acyltrifluoroborates from Aldehydes through Copper(I)-Catalyzed Borylation/Oxidation

Potassium acyltrifluoroborates (KATs) were prepared through copper(I)-catalyzed borylation of aldehydes and subsequent oxidation. This synthetic route is characterized by the wide range of aldehydes accessible, favorable step economy, mild reaction conditions, and tolerance of various functional groups, and it enables the facile generation of a range of KATs, for example, bearing halide, sulfide, acetal, or ester moieties. Moreover, this method was applied to the three-step synthesis of various α-amino acid analogues that bear a KAT moiety on the C-terminus by using naturally occurring amino acids as the starting material.