An on-water [4 + 2] annulation reaction between 2-methyl-3H-indolium salt and α-bromo N-acyl hydrazone has been developed. The environmentally friendly strategy provides the first facile access to spiro(indoline-2,3'-hydropyridazine) scaffolds.

An efficient formal (3 + 1 + 1) carboannulation strategy of Morita–Baylis–Hillman (MBH) carbonates with pyridinium ylides was developed for constructing diversely functionalized spiro-cyclopentadiene oxindoles. The reaction initiates with an SN2′ olefination of MBH carbonates with pyridinium ylides. The in situ generated dienes then engage in a challenging (4 + 1) ylide carboannulation, which has been rarely reported before. The reaction features broad substrate scope as well as high chemo- and regioselectivity. (3 + 1 + 1) carboannulation products could be easily transformed into interesting spiro-cyclopenta­[c]­furan oxindoles.

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An efficient one-pot, two-step, three-component reaction of isatin-derived MBH carbonates, sulfilimines, and epoxides was achieved, thus affording pharmaceutically important spiro-oxindole dihydropyridines.