An enantioselective tandem reduction/nitro-Mannich reaction of nitroalkenes using a simple thiourea organocatalyst

Abstract

There is a continual need for ever more effective and operationally simpler methods for the asymmetric synthesis of nitrogen containing molecules. We report here a generally efficient synthesis of stereochemically defined β-nitroamine building blocks which, through the combination of two catalytic transformations into one tandem process, results in the use of a simpler asymmetric catalyst, less reaction materials, shorter reaction times, circumvents the need for moisture sensitive reaction partners and leads to a wider substrate scope. Using para-methoxy-phenyl (PMP) protected imines, a Hantzsch ester as hydride source and a simple and economic thiourea organocatalyst, we have promoted the nitro-Mannich reaction with a nitroalkene to form anti-β-nitroamines. After protection as their trifluoroacetamides the products can be isolated in good yields (32–83%), high diastereomeric ratios (90 : 10 to >95 : 5) and excellent enantioselectivity (73–99% ee).