Syntheses and thermal behaviour of 9-substituted 9-thia-10-azaphenanthrenes

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Abstract
Synthetic approaches to a variety of 9-thia-l0-azaphenanthrenes having various kinds of substituent at the 9-position were investigated. Their thermal stabilities were found to depend strongly upon the nature of the substituents on the sulphur atom. Several 9-alkyl and 9-phenyl derivatives are quite stable at room temperature; in particular, the phenyl derivative was too stable to undergo thermal degradation. Refluxing in xylene for many hours effected some change of the 9-phenyl derivative 7ab to result in the formation of 1,4-rearranged 11 and N–S bond-cleaved 3ab products, while 9-alkyl derivatives 3c–3f were easily decomposed in refluxing benzene to undergo β-elimination to give 6H-dibenzo[c,e][1,2]thiazine 9 as major product. 9-Benzyl, 9-(4-substituted benzyl), 9-fluoren 9-yl and 9-cyanomethyl derivatives underwent, even at below room temperature, 1,2-rearrangement of the 9-substituent to afford the corresponding 6-substituted 6H-dibenzo[c,e][1,2]thiazines 10g–10o, 10w, which are very rarely observed in sulphilimine chemistry. A 9-silyl-group-substituted derivative was also too unstable to be isolated and caused a 1,2-imino shift to give the ringexpanded product 18. 9-Acylmethyl derivatives underwent Sommelet–Hauser-type rearrangement to afford benzothienoindole derivatives 24.

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