B(C₆F₅)₃‐Catalyzed Deoxygenative Reduction of Amides to Amines with Ammonia Borane

Abstract

The first B(C 6 F 5 ) 3 -catalyzed deoxygenative reduction of amides into the corresponding amines with readily accessible and stable ammonia borane (AB) as a reducing agent under mild reaction conditions is reported. This metal-free protocol provides facile access to a wide range of structurally diverse amine products in good to excellent yields, and various functional groups including those that are reduction-sensitive were well tolerated. This new method is also applicable to chiral amide substrates without erosion of the enantiomeric purity. The role of BF 3 · OEt 2 co-catalyst in this reaction is to activate the amide carbonyl group via the in situ formation of an amide-boron adduct.

Amine–Boranes as Transfer Hydrogenation and Hydrogenation Reagents: A Mechanistic Perspective

“…The authors proposed the formation of a zwitterion species of type 17 resulting from hydride abstraction of H 3 N•BH 3 from the Lewis base/Lewis acid adduct. A similar hypothesis was proposed by Shi and coworkers in the development of N-heteroarene reduction, [50] by Xiao and co-workers for the deoxygenation of amides and lactams, [51] and by Zhong and co-workers for the reductive amination of ketones. [52] Du, Meng, and co-workers reported an asymmetric and stereoselective TH of imines using H 3 N•BH 3 (Scheme 18 a).…”

Defunctionalisation catalysed by boron Lewis acids

“…50 Xu, Fan, Xiao, and co-workers reported the reduction of various amides with ammonia borane as the reductant in the presence of catalytic amounts of B(C 6 F 5 ) 3 and BF 3 $OEt 2 to provide a wide range of structurally diverse amines in good to excellent yields under mild reaction conditions with high functional-group tolerance (Scheme 22). 51 The role of the BF 3 $OEt 2 co-catalyst is to activate the carbonyl group of amide by Lewis adduct formation.…”

Indirect reduction of CO2and recycling of polymers by manganese-catalyzed transfer hydrogenation of amides, carbamates, urea derivatives, and polyurethanes

“…21,[58][59][60] Most recently, significant contributions were made in the transfer hydrogenation of amides. [61][62][63] Klankermayer and co-workers reported an efficient Ru-catalyzed transfer hydrogenation of cyclic amides to cyclic tertiary amines, 61 while the groups of Xu, Fan and Xiao reported the Ru- 62 and B(C 6 F 5 ) 3 - 63 catalyzed reduction of aliphatic amides to amines. Notably, in all cases a selective C-O cleavage was observed over the possible C-N bond cleavage.…”