Boronate Urea Activation of Nitrocyclopropane Carboxylates

Abstract

Boronate ureas operate as catalysts for the activation of nitrocyclopropane carboxylates in nucleophilic ring-opening reactions. A variety of amines were found to open the urea-activated nitrocyclopropane carboxylates, generating highly useful nitro ester building blocks in good yields. Standard manipulations allow access to a wide range of valuable compounds from the ring-opened products with direct applications in bioactive target synthesis.

Ring-opening, cycloaddition and rearrangement reactions of nitrogen-substituted cyclopropane derivatives

“…Another system has been recently developed, relying on a functionalised urea-based catalyst 178 acting as a strong hydrogen-bond donor. Although the transformations are slower than with Ni(ClO 4 ) 2 and require the presence of trifluoroethanol, this catalyst can, in principle, be engineered, which could be an advantage for the optimisation of specific reactions 289. 290 The method has been applied to the synthesis of the CB-1 receptor inverse agonist 179 (Scheme 121).…”

Ring Opening of Donor–Acceptor Cyclopropanes with N-Nucleo­philes

“…. 82,83 The activation pathway for cyclopropanes 50 involves coordination of urea 54 with the nitro group of the cyclopropane (Scheme 24). The presence of a difluoroboryl substituent at the ortho site in the aryl group increased the efficiency of the reaction by 20%, which was ascribed to an increase in the acidity of the hydrogen atoms in the amide group, owing to the coordination of boron with the oxygen atom in the carbonyl group in 54.…”

“…82 The Tang group has developed an asymmetric catalytically induced version for the nucleophilic ring opening of activated cyclopropanes with amines. [84][85][86] Conditions analogous to those suggested in Charette's method 80 facilitated ring opening for cyclopropane-1,1-diesters 57a-n by secondary amines yielding 58а-w.…”

A Simple and Efficient Synthesis of Diaryl Ureas with Reduction of the Intermediate Isocyanate by Triethylamine

“…12,13 Moreover, urea derivatives also impart important function in organic synthesis as intermediates and bifunctional organocatalysts. [14][15][16][17] Typically, efficient synthesis of the urea functional group is achieved through the condensation of an amine with an isocyanate, or the coupling of amines with phosgene or a phosgene equivalent. 18,19 Unfortunately, phosgene poses handling issues due to its toxicity, so developing a less hazardous synthetic route to ureas has attracted considerable interest over the years.…”