Naphtho- and Dibenzo-l,2-thiazines

Compounds in this section are discussed in order of the point of fusion of an aromatic ring to the 1,2-benzothiazine nucleus. Klivenyi and coworkers,121 in attempting to prepare derivatives of papaverine-6 -sulfonic acid (134), reacted 134 with chlorosulfonic acid and isolated in good yield 2, 3,10, 1 l-tetraalkoxy-7, 8-dihydroisoquinolino [2,1-b] [1,2]benzothiazine 8,8-dioxide (135), a naphtho-1,2-benzothiazine analog (Eq. 33). 

Abramovitch and co-workers,122 investigating the chemistry of aryl-nitrenes and sulfonylnitrenes, thermolyzed biarylsulfonyl azides (136) which at 120°C produced 6H-dibenzo[c,e] [ 1,2]thiazine 5,5-dioxide (138) (80%) via the proposed intermediate 137 (Eq. 34). N-Alkylation of 138 with 

Kaufmann and Zobel124 first prepared 2,3-dihydro-3-oxonaphtho-[l,8-d,e][ 1,2]thiazine 1,1-dioxide (146). More recently, this was prepared by Lombardino125 by an abbreviated process involving lithiation of 144 and treatment with carbon dioxide (Eq. 35). Cyclization of 145 with poly-phosphoric acid simultaneously removed the tert-butyl group to produce compound 146 directly. 

Trummlitz and co-workers126 also prepared derivatives of 150 by treatment of 2-methyl-2H-naphtho [2,1-c] [l,2]thiazin-4-(3H)-one 1,1-dioxide (151) with sodium hydride and an aryl isocyanate. The starting material (151) for this sequence was synthesized analogously to the related benzo-thiazine 11. 

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