Formal Homologous Aldol Reactions: Interrupting the Nazarov Cyclization via Carboalkoxylation of Alkynes

Reactions
between 1,4-pentadien-3-ones and aryl acetylenes in the
presence of BF3·OEt2 furnish α-phenacyl
cyclopentanones via a domino electrocyclization/carboalkoxylation
reaction sequence. The overall process underscores a new mode of interrupted
Nazarov trapping, where two new carbon–carbon bonds are installed
with concomitant formation of carbonyl functionality.