α-Borylcarbonyl compounds: from transient intermediates to robust building blocks

Abstract

α-Borylcarbonyl species (C-bound boron enolates) are typically unstable due to their kinetic and thermodynamically favourable rearrangement to their O-bound isomers. Direct evidence of α-borylcarbonyl compounds is sparse despite the multitude of transformations in which they have been implicated as reactive intermediates. In recent years, a few examples have emerged of reactive α-borylcarbonyl intermediates that can be observed using spectroscopic methods. Other reports have shown that certain compounds containing the α-borylcarbonyl motif can be isolated under ambient conditions. Installation of electron-rich, tetracoordinate sp(3)-boron centers is a particularly viable strategy to improve the stability of α-borylcarbonyl systems as it imposes a barrier to the otherwise rapid 1,3-boron shift from carbon to oxygen. Among stable α-borylcarbonyl compounds, α-boryl aldehydes, equipped with a tetracoordinated N-methyliminodiacetyl (MIDA) boryl group, have been demonstrated to be versatile building blocks in the synthesis of a wide range of functionalized organoboron compounds.

Oxidative Difunctionalization of Alkenyl MIDA Boronates: A Versatile Platform for Halogenated and Trifluoromethylated α‐Boryl Ketones

“…[7] Hence,t he formation of C-boron enolates (a-boryl carbonyls) provides ag reater challenge to the synthetic chemist. [8] However,t hey have potentially good synthetic value because they are kinetically amphoteric,m eaning that they contain an ucleophilic site adjacent to an electrophilic center (the nucleophilic boronate and the electrophilic carbonyl) and hence exhibit multiple modes of reactivity. [9]…”

Vibrational Circular Dichroism Unveils Chiroptical, Electrical, and Magnetic Properties of Borylated Isocyanides and Aldehydes

“…As part of our research program in chemical synthesis, we have developed air‐ and moisture‐stable α‐boryl aldehydes . In these compounds, premature reactivity between the nucleophilic and electrophilic functional groups is prevented through the use of N ‐methyliminodiacetic acid (MIDA).…”

Oxidative Difunctionalization of Alkenyl MIDA Boronates: A Versatile Platform for Halogenated and Trifluoromethylated α‐Boryl Ketones

“…[1, 2] With regards to enolizable carbonyls that can generate boron enolates,t here is ar apid equilibrium between the O-and Cbound forms,with the latter being much less thermodynamically stable because of the stronger OÀBb onds over CÀB bonds. [8] However,t hey have potentially good synthetic value because they are kinetically amphoteric,m eaning that they contain an ucleophilic site adjacent to an electrophilic center (the nucleophilic boronate and the electrophilic carbonyl) and hence exhibit multiple modes of reactivity. [8] However,t hey have potentially good synthetic value because they are kinetically amphoteric,m eaning that they contain an ucleophilic site adjacent to an electrophilic center (the nucleophilic boronate and the electrophilic carbonyl) and hence exhibit multiple modes of reactivity.…”

“…[7] Hence,t he formation of C-boron enolates (a-boryl carbonyls) provides ag reater challenge to the synthetic chemist. [8] However,t hey have potentially good synthetic value because they are kinetically amphoteric,m eaning that they contain an ucleophilic site adjacent to an electrophilic center (the nucleophilic boronate and the electrophilic carbonyl) and hence exhibit multiple modes of reactivity. [9] Generally,the formation of stable,isolable a-boryl carbonyls remains an underexplored area of research, despite the fact that they have been suggested or (in some cases) shown to be implicated as reactive intermediates in many transformations.…”