title: Organocatalytic asymmetric formation of steroids.
abstract: A novel and simple one-step approach for the construction of optically active steroids in a highly stereoselective manner by using organocatalysis is presented. The reaction of (di)enals with cyclic dienophiles in the presence of a TMS-protected prolinol catalyst leads to the construction of important 14 β-steroids. This new reaction allows an easy access to optically active steroids with a variety of substituents in the A ring in high yields and up to greater than 99 % ee. The reaction has been extended to include the construction of B- and D-homosteroids as well as steroids containing heteroatoms in the B ring. The angular substituent at C13 can be varied and alkyl, ester, and sulfone functionalities are introduced with excellent stereoselectivities. Simple synthetic procedures provide access to a range of naturally occurring steroids such as estrone and related analogues.
authors.affiliation: Center for Catalysis, Department of Chemistry, Aarhus University, Langelandsgade 140, 8000 Aarhus C (Denmark).
authors.forename: Kim Søholm
authors.initials: KS
authors.lastname: Halskov
authors.forename: Bjarke S
authors.initials: BS
authors.lastname: Donslund
authors.forename: Sebastian
authors.initials: S
authors.lastname: Barfüsser
authors.forename: Karl Anker
authors.initials: KA
authors.lastname: Jørgensen
keywords: asymmetric synthesis; cycloaddition; organocatalysis; steroids; synthesis design