Catalytic asymmetric hydrogenation of (Z)-α-dehydroamido boronate esters: direct route to alkyl-substituted α-amidoboronic esters

Abstract

The direct catalytic asymmetric hydrogenation of (Z)-α-dehydroamino boronate esters was realized.

Catalytic Approach to Diverse α‐Aminoboronic Acid Derivatives by Iridium‐Catalyzed Hydrogenation of Trifluoroborate‐Iminiums

“…Recently, the challenge of α‐aminoboronic acid synthesis was tackled by reductive amination of acylboranes (Scheme 1, entries 1 and 2), [10,11] borylation of amides, [12–14] hydroboration of enamides, [15] electrophilic amination of gem ‐diborylalkanes (Scheme 1, entry 3), [16] a cascade copper‐catalyzed aminoboration of alkynes, [17] and also an interesting one‐pot borono‐Strecker reaction [18] . Two complementary rhodium‐catalyzed approaches were disclosed independently by two research groups, successfully hydrogenating α‐boryl enamides (Scheme 1, entry 4) [19,20] . Very recently, based on a previously reported decarboxylative borylation, [21] a solid‐phase approach to aminoboronate‐containing peptidomimetics has been developed (Scheme 1, entry 5) [22] …”

“…Reduction of TIMs with KBH 4 led to stable and isolable trifluoroborate‐ammoniums (TAMs) [11] . TAMs proved to be easy to use and more convenient intermediates than the corresponding boronic ester counterparts in several reports (Scheme 1, entry 3) [16,19,23] . Bode et al.…”

Recent Developments in Transition-Metal-Catalyzed Asymmetric Hydrogenation of Enamides

“…The AH of compounds having a chiral oxazolidin-2one moiety bearing bulky phenyl substituents afforded the reduced products with diastereomeric ratios ranging from 7:1 to 44:1 (Scheme 4). 12 The developed clean, atom-economical and environmentally friendly catalytic asymmetric hydrogenation process gave access to products whose utility was successfully demonstrated by transformation into their corresponding boronic acid derivatives via a Pd-catalyzed borylation reaction (not shown) and an efficient synthesis of a potential intermediate of bortezomib (Scheme 5). 12…”

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

“…11,18 In recent years, this field has continued to flourish with many exciting methods being developed. 19–33 Among recent methodologies, discoveries of Yudin 32 and Bode 33 caught our attention. Namely, in these reports trifluoroborate-iminiums (TIMs) and MIDA-protected iminoboronates were prepared from acylboranes, 34 and converted to racemic N -substituted α-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. 11,18–33,35…”