Multifaceted α‑Enaminone: Adaptable Building Block for Synthesis of Heterocyclic Scaffolds Through Conceptually Distinct 1,2‑, 1,3‑, 1,4‑, and C–O Bond Forming Annulations

The
new reactivity of α,β-unsaturated
enaminones driven by their “dual electronic attitude”
is reported. We introduce unexplored, α-enaminone synthones
and reveal the unusual functionalities of these building blocks. The
feasibility of this new concept is demonstrated in the direct functionalization
of enaminone precursors, such as alkylation; 1,2- 1,3-, or 1,4-addition;
and C–O bond formation. The general and potential applicability
is presented through the collective synthesis of several important
classes of heterocycles via controlled cyclizations of easily accessible
common precursors. The rapid composition of novel key α-enaminone
synthones yields an assembly of oxazines, azaspirones, quinolinones,
and quinolinols in a regio- and chemoselective fashion.