Enantioselective catalytic 1,2-boronate rearrangements

Abstract

Asymmetric carbon coupling at boron The Matteson reaction produces carbon–carbon bonds by coupling halocarbons such as widely available dichloromethane with an alkyl substituent on boron. Sharma et al . report asymmetric catalysis of this reaction. Their catalyst, derived from a chiral thiourea, a boronic ester, and an alkyl lithium base, appears to accelerate a chloride abstraction step through its lithium center. The product, still bearing a chloride, can be further modified through stereospecific displacement to generate a wide variety of trisubstituted chiral centers. —JSY

Primary trifluoroborate-iminiums enable facile access to chiral α-aminoboronic acids via Ru-catalyzed asymmetric hydrogenation and simple hydrolysis of the trifluoroborate moiety

“…Many of the existing methods are either racemic, allow limited scope of substrates, or do not enable the synthesis of N -unprotected derivatives. 11,18–33,35…”

“…11,18 In recent years, this eld has continued to ourish with many exciting methods being developed. [19][20][21][22][23][24][25][26][27][28][29][30][31][32][33] Among recent methodologies, discoveries of Yudin 32 and Bode 33 caught our attention. Namely, in these reports triuoroborate-iminiums (TIMs) and MIDA-protected iminoboronates were prepared from acylboranes, 34 and converted to racemic N-substituted a-aminoboronic acid derivatives with borohydride reagents (Scheme 1).…”

“…Many of the existing methods are either racemic, allow limited scope of substrates, or do not enable the synthesis of N-unprotected derivatives. 11,[18][19][20][21][22][23][24][25][26][27][28][29][30][31][32][33]35 Based on our recent research, 35 we envisioned that unsubstituted primary TIMs (pTIMs) could provide access to chiral aaminoboronic acids using asymmetric hydrogenation. Moreover, the use of pTIMs would eliminate the N-deprotection step to obtain the free amino group, thereby shortening the overall synthetic sequence.…”

Carbene reactivity from alkyl and aryl aldehydes

“…However, a protons are rarely tolerated owing to 1,2-H migration of the Zn carbenoid (16). Despite elegant solutions for Matteson rearrangement by Li-boronate carbenoids (17)(18)(19)(20), Mo-mediated ketone deoxygenation (21,22), and Au-catalyzed alkyne cyclizations (23,24), there remains no general approach to access nonstabilized alkyl carbenes or for their use in the wide range of carbene reactivity available to stabilized diazo reagents (25).…”

Stereoselective gem-C,B-Glycosylation via 1,2-Boronate Migration

“…Since the pioneering work by Hillman and Matteson, organoboron homologation reactions via 1,2-boronate migration have developed into a reliable route for the synthesis of organoboron compounds. , The retained boron unit allows for a broad array of downstream transformations . Typically, a suitable electrophilic leaving group is required for stereospecific 1,2-migration after nucleophilic addition to the empty p-orbital of the boron center …”