Amine hemilability enables boron to mechanistically resemble either hydride or proton

Abstract

Tetracoordinate MIDA (N-methyliminodiacetic acid) boronates have found broad utility in chemical synthesis. Here, we describe mechanistic insights into the migratory aptitude of the MIDA boryl group in boron transfer processes, and show that the hemilability of the nitrogen atom on the MIDA ligand enables boron to mechanistically resemble either a hydride or a proton. The first case involves a 1,2-boryl shift, in which boron migrates as a nucleophile in its tetracoordinate form. The second case involves a neighbouring atom-promoted 1,4-boryl shift, in which boron migrates as an electrophile in its pseudo-tricoordinate form. Density functional theory studies and in situ NMR measurements all suggest that MIDA can act as a dynamic switch. These findings encouraged the development of novel migration processes involving boron that exploit the chameleonic behaviour of boron by acting as both a nucleophile and an electrophile, including the first report of a compound with a boronate functionality bound to carbon in the carboxylic acid oxidation state.

Regio- and stereoselective synthesis of tetra- and triarylethenes by N-methylimidodiacetyl boron-directed palladium-catalysed three-component coupling

“…1b). Computational analysis reveals a drastic electron donation from the C−Pd σ bond to a boron centered p-orbital the transition state due to the hemilabile nature of the MIDA B−N dative bond 56 . A similar regioselectivity trend was also observed in our previous rhodium (III)-catalysed C-H annulation reaction with alkyne MIDA boronates 44 .…”

Sterically Unprotected Nucleophilic Boron Cluster Reagents

“…This led us to the development of a simple protocol, whereby carbon-based electrophiles can be transformed into the corresponding tricoordinate boron ester species without the use of metal catalysis. This work highlights how boron-rich clusters can expand the toolkit of main group reagents [29][30][31][32][33][34][35][36][37][38][39][40][41][42][43][44][45][46][47] ultimately aiding in the development of organic synthesis through new modes of reactivity.…”

Cycloadditions of Alkenylboronic Derivatives

“…MIDA boronates 60 also appeared to be suitable substrates for epoxidation; in this case, mCPBA was appropriate oxidant to achieve this transformation (Scheme 27). [61][62][63][64][65][66] The method was compatible with a wide range of substrates including mono-, di-, and trisubstituted derivatives with alkyl, aryl, SiMe 3 , Cl, and other substituents.…”