Green and effective synthesis of multisubstituted a-pyrones via K2CO3 catalyzed formal insertion of ketenimines into C(CO)-C bonds of 1,3-diketones

Cleavage of C(CO)-C bonds is a fascinating transformation that offers exciting opportunities for development of new synthetic methodologies through reconstruction of the molecular skeleton. However, the catalytic insertion of heteroallenes into C(CO)-C bonds of unstrained 1,3-diketones is so far challenging and still unknown. Herein, we report an environmentally friendly and green synthetic approach to prepare racemic or enantioenriched 3,4,6-trisubstituted a-pyrones through the cheap K2CO3-catalyzed formal C(CO)-C bond insertion reaction of ketenimines with 1,3-diketones. In addition, a one-pot procedure leading to either 3,4,6-trisubstituted a-pyrones or 4,6-disubstituted a-pyrones through an unprecedented sequential Pd(0) or Co(ii)/K2CO3 catalysis has also been developed. The synthetic utility of this methodology was demonstrated by the broad substrate scope, the concise synthesis of analogues of pharmaceutically active compounds, and the diverse derivatization of the pyrone framework. More importantly, this work not only opens up a new avenue for designing structurally non-traditional a-pyrones, but also unlocks the huge potential of some extended p-conjugated a-pyrones with optoelectronic application in organic light-emitting diodes.