Synthesis and structure of new alkynyl derivatives of phenothiazine and phenoxazine

New alkynyl derivatives of phenothiazine and phenoxazine were obtained via Sonogashira cross-coupling reactions. This was achieved by first synthesizing the intermediates 6-chloro-5H-benzoa]phenothiazin-5-one, 6-chloro-5H-benzoa]phenoxazin-5-one and 6-chloro-5H-naphtho2,1-b]pyrido2,3-e]1,4]oxazin-5-one by anhydrous base-catalyzed condensations between 2,3-dichloro-1,4-naphthoquinone and 2-aminothiophenol, 2-aminophenol and 2-aminopyridinol, respectively .The cross-couplings of these electron-rich chlorophenothiazine and chlorophenoxazine intermediates with terminal alkynes, employing 4?mol% Pd and 7?mol% XPhos in the presence of base in acetonitrile at 80°C, afforded the highly colored alkynylated derivatives in good yields. These reaction conditions allowed the incorporation of both unprotected N-H and carbonyl groups. Structural assignments were established by spectroscopic (UV, IR, ¹H and ¹³Cnmr), ms and elemental analytical data.