A DIELS-ALDER APPROACH TO STEMONA ALKALOIDS - TOTAL SYNTHESIS OF STENINE

A total synthesis of dl-stenine (4) is described. Key features involve (1) use of an intramolecular Diels-Alder cycloaddition-aminimide rearrangement sequence to construct the perhydroindole substructure (29 --> 36 --> 27), (2) application of an Eschenmoser-Claisen rearrangement-iodolactonization sequence to prepare the butenolide substructure (58 --> 59 --> 61), (3) use of a free-radical allylation to introduce the C(9)-ethyl group (61 --> 62), and (4) thermal cyclization of an amino ester to afford azepinone 68. A variety of intermolecular and intramolecular Diels-Alder reactions, including examples in which alpha,beta-unsaturated thioesters play the role of dienophile, are also described.