An Asymmetric Total Synthesis of D-Homo Steroids Involving a Lewis Acid Directed Diels-Alder Reaction

Abstract

In recent years, applications of asymmetric, amino acid mediated aldol cyclizations^1,2 have led to major advances in steroid total synthesis.³ Typical of such processes is the conversion of prochiral triketone la ⁴ to the steroid CD-synthon, (S)-(+)-enedione 2a in high chemical and optical yield, under the influence of (S)- proline.^1,2 This approach to the introduction of chirality is the foundation upon which several enantiospecific and highly efficient syntheses of biologically important steroids (19-norsteroids, A-ring aromatic steroids, androstanes) or their precursors are based.³