Sequential Michael Addition/Electrophilic Alkynylation: Synthesis of α-Alkynyl-ß-Substituted Ketones and Chromanones.

ABSTRACT

We describe the synthesis of α-alkynyl-ß-substituted cyclic ketones and analogue chromanones via one-pot Michael addition/hypervalent iodine-based α-alkynylation. Cu(I)-catalyzed Michael addition using either alkyl-aluminum or Grignard reagents, followed by diastereoselective electrophilic alkynylation of the resulting enolate by 1-ethynyl-1λ3,2-benziodoxol-3(1H)-one (EBX) resulted in the α-alkynyl-ß-substituted cyclic ketones or chromanones within 34-89% yield (16 examples). The reaction was successfully upscaled to the 5 mmol scale, and further functionalization of a model alkynylated ketone was demonstrated.