The DMAP-catalyzed [3+3] annulation of cyclopropenones with α-bromoketones was developed for a convenient synthesis of 2-pyrones. The mechanism may proceed in a pyridium ylide-initiated ring opening of cyclopropenones, followed by elimination of DMAP catalyst, and final 6π-electrocyclization.
Catalytic [3+3] Annulation of
<scp>β‐Ketoethers</scp>
and Cyclopropenones
<i>via</i>
C(sp
<sup>3</sup>
)—O/C—C Bond Cleavage under
<scp>Transition‐Metal</scp>
Free Conditions
carbon-oxygen (C—O) bond is highly important for the transformation of oxygen-rich biomass and industry chemicals. Herein, an efficient [3+3] annulation of β-ketoethers with cyclopropenones in the presence of catalytic base has been developed, which proceeds through the C(sp3)—O bonds cleavage in β-ketoethers and C—C bond cleavage in cyclopropenones under transition-metal free conditions. The cleavage of C(sp3)—O
A simple and efficient synthesis for 2-pyrones by [3 + 3] annulation of cyclopropenones and sulfur ylides in the presence of triethyl amine as a base has been developed featuring transition-metal free conditions, high yields, and excellent functional group compatibility. Using this process, a variety of 2-pyrones were prepared in good to excellent yields.