Selective Construction of Diverse Polycyclic Spirooxindoles via a Three-Component Reaction of Cyclic Mercapto-Substituted β‑Enamino Esters, Isatins, and Cyclic 1,3-Diketones

The three-component reaction of alkyl 2-(benzo­[b]­[1,4]­thiazin-3-ylidene)­acetates, isatins, and 1,3-indanedione (1,3-cyclopentanedione) in ethanol in the presence of acetic acid conveniently afforded spiro­[indeno­[1,2-b]­phenothiazine-6,3′-indolines] or spiro­[cyclopenta­[b]­phenothiazine-4,3′-indolines] in good yields and with high diastereoselectivity. More interestingly, a similar three-component reaction with 4-hydroxychromen-2-one resulted in the unexpected polycyclic spiro­[benzo­[b]­chromeno­[3′,4′:5,6]­pyrano­[2,3-e]­[1,4]­thiazine-7,3′-indolines] in satisfactory yields. A plausible reaction mechanism was rationally proposed for formation of different kinds of the spiro compounds, and the stereochemistries of the various spiro compounds were clearly elucidated.