Asymmetric Total Synthesis of the Iridoid β-Glucoside (+)-Geniposide via Phosphine Organocatalysis

Phosphine-catalyzed [3 + 2] cycloaddition of ethyl-2,3-butadienoate with enone (S)-3b occurs with high levels of regio- and stereocontrol to deliver the cis-fused cyclopenta[c]pyran 4 characteristic of the iridoid family of natural products. Cycloadduct 4 was converted to the iridoid glycoside (+)-geniposide in 10 steps.