187658-74-8Relevant academic research and scientific papers
Synthesis of Regioisomeric 2,5-bis-substituted-aza-benzothiopyranoindazoles
Krapcho,Haydar
, p. 1153 - 1166 (2007/10/03)
The synthesis of 6-chloro-9-nitro-benzothiopyranopyridin-5-ones 2a, 2b and 2c has been accomplished. Chemotype 2d could not be prepared since attempts to cyclize 3-(2-nitro-5-chlorophenoxy)pyridine-2-carboxylic acid (1d) led to the decarboxylation product 3-(2-nitro-5-chlorothiophenoxy) pyridine (40). Analogues 2a, 2b or 2c on treatment with the respectively substituted hydrazine led to the 2-(substituted)-5-nitro 7, 8- or 9-aza substituted chemotypes 3a-7a, 8b, and 9c-13c. The reduction of the nitro groups of these substrates was effected by treatment with hydrogen gas (palladium catalyst) or by stannous chloride to yield the 5-amino chemotypes 15a-18a, 20b and 21c-24c, respectively. The conversion of these derivatives to the 2,5-bis (alkylamino)-7-, 8- and 9-aza benzothiopyranoindazoles listed in Table 3 was accomplished by direct alkylations, acylations, followed by reduction of the amido group with Red-Al or lithium aluminum hydride, or by reductive alkylations in the presence of sodium cyanoborohydride. The removal of the protective BOC-group was effected by treatment of the appropriate substrates with anhydrous hydrogen chloride to afford the respective hydrochloride salts listed in Table 4.
