Total synthesis of (+/-)-stenine using the IMDAF cycloaddition of a 2-methylthio-5-amido-substituted furan

reaction: see text]. The intramolecular 4 + 2]-cycloaddition of a 2-methylthio-5-amidofuran was used to create the azepinoindole skeleton present in the Stemona alkaloid stenine. The rearranged cycloadduct was converted to stenine (1) in 11 additional steps via a sequence that features a Crabtree catalyst directed hydrogenation (9-->10), iodolactonization (2-->11), and a Keck allylation (11-->12).