Substrate-Controlled Domino Reaction of N-Sulfonyl Ketimines with 2-Aroyl-1-chlorocyclopropanecarboxylates: Access to Cyclopenta[c]chromenes and Benzo[f]cyclopenta[d][1,2]thiazepine Dioxides

An unprecedented substrate-controlled annulation method for the synthesis of fascinating classes of angularly fused cyclopenta[c]chromenes and benzo[f]cyclopenta[d][1,2]thiazepine 5,5-dioxide derivatives in good to high chemical yields is reported. This Michael-initiated ring-expansion reaction would enable two C-C and one C-O or C-N bonds by a judicious choice of carbonucleophiles, either 4-alkyl or 3-alkyl-substituted N-sulfonyl ketimines, respectively, with a series of donor-acceptor cyclopropane scaffolds as 4C sources promoted by DBU. Moreover, this eco-friendly method is mild enough to protect different kinds of functionalities. Importantly, the prepared fused fulvene scaffolds were smoothly transformed into a special class of hexahydrocyclopenta[c]chromenes as single cis-cis-cis-cis diastereomers in excellent yields by a simple catalytic hydrogenation reaction.