Cascade Cyclization of -(2-Acyl-1-ethynyl)benzaldehydes with Amino Acid Derivatives: Synthesis of Indeno[2,1-]pyran-3-ones and 1-Oxazolonylisobenzofurans via the Erlenmeyer-Plöchl Azlactone Reaction.

A highly regioselective divergent approach is reported for the synthesis of both indeno[2,1-]pyran-3-one and 1-oxazolonylisobenzofuran derivatives using the Erlenmeyer-Plöchl azlactone (EPA) reaction. This approach involves the synthesis of -(2-acyl-1-ethynyl)benzaldehydes, which reacted with various amino acids. Reaction with -acylglycines resulted in the formation of indeno[2,1-]pyran-3-ones, involving the sequential formation of two C-C bonds and two C-O bonds. Conversely, when the same conditions were applied to free amino acids, 1-oxazolonylisobenzofurans were obtained. This reaction involved the formation of a C-C bond between oxazolone and -(2-acyl-1-ethynyl)benzaldehyde, followed by the formation of a C-O bond through a selective 5 cyclization.