The nitro-Mannich reaction and its application to the stereoselective synthesis of 1,2-diamines

The addition of alkyl nitronate anions to PMB imines, derived from benzaldehyde or straight-chain carbaldehydes, in the presence of a Bronsted acid, proceeds in greater than 90% yield with up to 10:1 diastereoselection favoring the anti isomer. The mechanism of this addition reaction is intriguing and is under investigation. The moderately unstable p-nitro amines can be reduced with samarium diiodide and the PMB group removed with CAN, in good overall yields, to give sensitive 1,2-diamines without erosion of diastereoselectivity. This protocol represents a new, stereoselective synthesis of certain 1,2-diamines.