Domino Synthesis of Benzo-Fused β,γ-Unsaturated Ketones from Alkenylboronic Acids and N‑Tosylhydrazone-Tethered Benzonitriles

The transition-metal-free domino reaction between alkenylboronic acids and N-tosylhydrazones from o-(2-oxoalkyl)- and o-(3-oxoalkyl)­benzonitriles leads to β,γ-unsaturated indanones and tetralones featuring an α-“all-carbon” quaternary center. The employment of derivatives of α-substituted cyclopentanones and cyclohexanones led to the stereoselective preparation of β,γ-unsaturated tetrahydro­cyclo­penta­[a]­inden-8­(1H)-ones, hexahydro­fluorenones, and hexahydro­anthracenones as cis-fused single stereoisomers. A domino sequence involving diazo compound formation/reductive alkenylation/1,3-borotropic rearrangement/intramolecular bora-aza-ene reaction is proposed to justify the formation of the products as well as the stereoselectivity.