Stereocontrolled construction of six vicinal stereogenic centers on a hexahydroxanthone framework through a formal [2+1+3] annulation†
The first example of a bifunctional donor–donor 3C synthon in situ from activated methine (methyleneindolinone and methylenebenzofuranone) with nitromethane through a [2+1] Michael addition, which further directed the following organocascade Michael/Henry cycloaddition reaction in a one-pot operation is developed, serving as a fruitful strategy for facile access to optically active and structurally diverse hexahydroxanthones with up to six contiguous stereocenters, including a quaternary one. A series of diversely functionalized products are smoothly obtained with up to 76% yield, >20 : 1 d.r. and 98% ee from simple and readily available starting materials. In addition, this is the first example of 3-formyl chromone as an acceptor–acceptor 3C building block, and also the first asymmetric catalytic construction of six vicinal stereogenic centers on a hexahydroxanthone scaffold.