Applications of an asymmetric [2 + 2]-photocycloaddition. Total synthesis of (-)-echinosporin. Construction of an advanced 11-deoxyprostaglandin intermediate

The first total synthesis of the novel antitumor metabolite (-)-echinosporin (1) has been achieved. Asymmetric [2+2]-photocycloaddition of dihydrofuran acetonide (+)-8 to 2-cyclopentenone (7) constituted the cornerstone of the synthetic strategy. Mitsunobu lactonization of hemiacetal acid 43 generated the tricyclic framework of 1, which embodies a strain energy of ca. 17 kcal/mol as estimated by MNDO calculations. The successful synthetic venture permitted assignment of the absolute configuration of echinosporin