Michael addition of a-nitro ketones to conjugated enonesunder solventless conditions using silica

Conjugate addition of both linear and cyclic a-nitro ketones to conjugated enones, can be efficiently performed under heterogeneous, solvent-free and mild acidic conditions, by silica. The procedure allows good yields of 2-nitro-1,5-diones and, it worthy of note that no products arising from the cleavage of a-nitro cycloalkanones were observed under these reaction conditions. Moreover, during the work up, the need of extraction with an organic solvent can be avoided since the crude mixture can be directly charged to a chromatography column for immediate purification.