Novel fused and bridged phenothiazine derivatives were selectively synthesized via an acid-promoted reaction of alkyl 2-(benzo[b][1,4]thiazin-3-ylidene)acetate, aromatic aldehydes and cyclic diketones under different reaction conditions.

The acetic acid promoted reaction of 3-hydroxy-3-(indol-3-yl)indolin-2-ones and mercapto-substituted β-enamino esters showed very interesting molecular diversity. The reaction in ethanol at room temperature in the presence of acetic acid resulted...

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The three-component reaction of alkyl 2-(benzo[b][1,4]thiazin-3-ylidene)acetates, isatins, and 1,3-indanedione (1,3cyclopentanedione) 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.

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