Boronate Urea Activation of Nitro Compounds

Boronate ureas have been discovered as enhanced hydrogen bond donor (HBD) catalysts for the activation of various compounds containing nitro functional groups. The enhanced ability of boronate ureas to recognize and activate nitro compounds can be attributed to the internal coordination of the strategically placed boron to the urea carbonyl. Boronate ureas have elicited rate enhancements of up to 10 times that of traditional urea and thiourea HBD catalysts in the known addition of nitrogen heterocycles to nitroalkenes. This improvement in urea catalyst activity has allowed for the discovery of two new methodologies.;The urea activation of nitrocyclopropane carboxylates was discovered for nucleophilic ring opening by amine nucleophiles. The facile formation of alpha-amino acid precursors from nitrocyclopropane carboxylate precursors had never before been reported with HBD catalysts. This novel activation of nitrocyclopropane carboxylates led to the discovery of formal [3+3] dipolar cycloaddition reactions with nitrones for the efficient construction of oxazinanes. Additionally, boronate ureas have been demonstrated to activate nitrodiazoester compounds for N-H insertion/multicomponent coupling of anilines for the formation of alpha-aryl glycine compounds. Chiral phosphoric acid HBD catalysts were utilized for activation of nitrodiazoesters for stereoselective glycine formation. This methodology was expanded to develop double arylation of nitrodiazoesters through a transient N-H insertion intermediate.