Preparation of new nitrogen-bridged heterocycles. 53. Syntheses of 3-(benzylthio)thieno[3,4-b]indolizine derivatives and their intramolecular arene-arene interactions |
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Authors: | Kakehi Akikazu Ito Suketaka Suga Hiroyuki Miwa Takeyuki Mori Takashi Fujii Tsuneo Tanaka Nobuaki Kobayashi Tomoshige |
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Institution: | Department of Chemistry and Material Engineering, Faculty of Engineering, Shinshu University, Nagano, Japan. akakehi@gipwc.shinshu-u.ac.jp |
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Abstract: | Various ethyl 1-arylcarbonyl-3-(un)substituted methylthio]thieno3,4-b]indolizine-9-carboxylates were synthesized in good yields by a novel methodology in which the S-alkylation of 5-arylcarbonyl-4-ethoxycarbonylmethyl-3-(1-pyridinio)thiophene-2-thiolates with alkyl or benzyl halides, the 1,5-dipolar cyclization of the resulting pyridinium salts in the presence of a base, and the aromatization were performed. In the X-ray analyses of some 3-(benzylthio)thieno3,4-b]indolizine-9-carboxylates, a gauche and two anti conformers in relation to the exocyclic sulfide linkage were found. Interestingly, all of the 3-(benzylthio)thieno3,4-b]indolizine derivatives showed significant high-field shifts (delta up to 0.3 ppm) for the 5- and 6-proton signals compared with those of the 3-methylthio derivatives in the (1)H-NMR spectra and exhibited a definite absorption band near 425 nm in their UV spectra, indicating an intramolecular arene-arene interaction between the thieno3,4-b]indolizine and the phenyl ring. |
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