A simple one-pot, multi-component synthesis of cyano-functionalized bis-β-diketones

Mild, multi-component Knoevenagel condensation/Michael addition reactions of dibenzoylmethane (Hdbm) and methylene-active cyano molecules with formalin in ethanol gave cyano methylene-bridged bis-diketones. The syntheses of 1,1,5,5-tetrabenzoyl-3,3-dicyanopentane (1) and 1,1,7,7-tetrabenzoyl-3,5-dicyano-3,5-dimethoxycarbonyl-heptane (4) are reported. Increasing the reaction time with the reagents for 1 led to the formation of the ester (2,2-dicyano-4-benzoylbutyl) benzoate (2). The isolation of 2,2-dicyano-4,4-dipivaloyl-1-butanol (3a), the tert-butyl analogue of a proposed intermediate in the formation of 2, provides evidence for a possible reaction pathway. Methylene-bis(dibenzoylmethane) (mdbm) was obtained in good yield from the reaction between Hdbm and formalin, by the addition of the base triethylamine. The X-ray crystal structures of 1–4 and mdbm were determined using synchrotron radiation.