Cationic Iron(III) Porphyrin-Catalyzed [4 + 2] Cycloaddition of Unactivated Aldehydes with Simple Dienes

Cationic iron­(III) porphyrin was found to be an efficient
catalyst
for the highly chemoselective hetero-Diels–Alder-type reaction
of aldehydes with 1,3-dienes. The catalyzed process did not require
the use of electron-deficient aldehydes such as glyoxylic acid derivatives
or activated electron-rich 1,3-dienes such as Danishefsky’s
diene and Rawal’s diene. The high functional group tolerance
and robustness of the catalyst were demonstrated. Further, the potential
utility of the catalyst was demonstrated by performing the cycloaddition
in the presence of water and by carrying out cycloaddition of an unactivated
ketone such as cyclohexanone with a diene.