S. Bajpai, K. Joshi, R. Jain
1997
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0
Influential Citations
2
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Journal
Heterocyclic Communications
Abstract
The synthesis of some new fluorinated spiro-indole derivatives is reported. Cyclocondensation of 3-arylimino-2H-indol-2-ones, prepared by the treatment of various fluorinated anilines with isatins, with o-mercaptobenzoic acid in acidic ethanol was investigated for the first time. A novel spiro system, spiro[2H1,3-benzothiazine-2,3'-[3H-indole]-2',4(1'H,3H)-dione (4) was isolated. Further, the role offluorine in such cyclocondensation reactions has been studied. It was observed that 3-[2,3,4,5,6-pentafluorophenyl)-imino2H-indol-2-one, 2 afforded exclusively S-[3-(1,3-dihydro-2-oxo-(2H)indolyl)]-o-mercaptobenzoic acid 5 instead of the expected spiro compound as obtained with mono to tetra fluorinated imino indoles. The spiro compounds have been further subjected to methylation and morphomethylation. Introduction Fluorinated indole derivatives are reported to exhibit multifaceted pharmacological and biological activities (1-3). The role of fluorine in organic compounds is noteworthy in view of profound changes which are produced in biological activities on incorporation of fluorine at critical reaction sites (4). Earlier, we had studied the cyclization reactions of 3-arylimino-2H-indol-2-ones with mercaptoacetic acid (5,6) and mercaptopropionic acid (7). In the present investigation, the role of increasing the number of fluorine atoms during the cyclocondensation has been studied by the reaction of 3-arylimino-2H-indol-2-ones with o-mercaptobenzoic acid. Results and Discussion Suitable indole-2,3-diones and anilines, with varying degrees of fluorination, were reacted in acidic ethanol to give 3-arylimino-2H-indol-2-ones which were further treated with o-mercaptobenzoic acid by two methods : Without isolation of anil (one-step) and with isolation of anil (two-step). Both the methods afforded the same product: 3-aryl-4,5-dihydrospiro[2H-1,3-benzothiazine-2,3'-[3H]indole]-2',4(1 'H,3H)-diones (Schemel). However, the two-step method gave a better yield. All the compounds listed in Table 1 were synthesized via two step method. Methylation and morphomethylation yielding 1-substituted title spiro compounds 4h & 4i were also undertaken using two different routes: by starting with appropriate 1 -substituted indole-2,3diones followed by subsequent treatments and by methylation/morphomethylation of the spiro compounds prepared.