Preparation of new nitrogen-bridged heterocycles. 53. Syntheses of 3-(benzylthio)thieno[3,4-b]indolizine derivatives and their intramolecular arene-arene interactions

Preparation of new nitrogen-bridged heterocycles 67. syntheses of alpha,alpha'-Bis[(thieno[3,4-b]indolizin-3-yl)thio]-o-, m-, and p-xylene derivatives and their conformational structures

The alkaline treatment and dehydrogenation of pyridinium salts, formed from the S-alkylations of 3-(1-pyridinio)thiophene-2-thiolates with alpha,alpha-dibromo-o-, m-, or p-xylene, provided the corresponding alpha,alpha'-bis[(thieno[3,4-b]indolizin-3-yl)thio]-o-, m-, and p-xylene derivatives in low to good yields. Both (1)H-NMR and UV-Vis spectra of these products supported distinctly the predominance of the gauche-gauche conformation in relation to the two sulfide linkages as the spacer in these molecules. On the other hand, the X-ray analyses indicated the expected gauche-gauche conformation for the m- and the p-xylene derivatives, but the anti-anti one for the o-xylene derivative.

Preparation of new nitrogen-bridged heterocycles. 59. Syntheses and intramolecular interactions of 3-(acylmethylthio)- and 3-[(3-ethoxycarbonyl-2-propenyl)thio]thieno[3,4-b]indolizine derivatives

Various thieno[3,4-b]indolizine derivatives having an acylmethylthio or (3-ethoxycarbonyl-2-propenyl)thio group at the 3-position which could not be obtained by a conventional method were prepared by a new procedure using cyanoethyl group as a protecting group and their intramolecular arene-pi interactions were investigated. In the (1)H-NMR spectra of these thieno[3,4-b]indolizines, the low-field shifts (delta 0.10-0.33 ppm) for the 5-protons were observed in comparison with those of 3-(methylthio)thieno[3,4-b]indolizines as a standard. The UV spectra also exhibited a characteristic absorption band at 425-445 nm attributable to the arene-pi interaction but their intensities were generally lower than those of 3-(arylmethylthio)thieno[3,4-b]indolizines. In their X-ray analyses, the anti conformation for 3-(acylmethylthio)thieno[3,4-b]indolizines and the gauche one for the 3-(3-ethoxycarbonyl-2-propenyl)thio derivatives were exhibited.

Preparation of new nitrogen-bridged heterocycles. 58. Syntheses and intramolecular arene-pi interactions of 3-(allylthio)- and 3-(propargylthio)thieno[3,4-b]indolizine derivatives

Various thieno indolizine derivatives having an allylthio or propargylthio group at the 3-position were prepared and their intramolecular arene-pi interactions were investigated. Their 1H-NMR spectra showed significant low-field shifts (delta 0.10-0.34 ppm) to the 5-proton on the thieno indolizine ring, and this effect was the reverse to that observed in 3-(arylmethylthio)thieno indolizines. However, their UV spectra exhibited a characteristic absorption band due to the arene-pi interaction near 430 nm and these values were almost similar to those for arene-arene interaction of 3-arylmethylthio derivatives though their molar extinction coefficients were largely varied by the 3-substituents. Furthermore, both types of gauche conformations in which the intramolecular arene-pi interactions are possible in one form and impossible in the other were confirmed by X-ray analyses of some compounds.

Synthesis of a library of benzoindolizines using poly(ethylene glycol) as soluble support

A library of benzoindolizines (pyrrolo [1,5-a] quinolines 10 and pyrrolo [1,5-a] quinolines 9) has been synthesized using poly(ethylene glycol) (PEG) as soluble polymer support. The PEG-supported isoquinolinium salt 4 reacted, respectively, with active alkenes 11 using tetrakispyridinecobalt(II) dichromate (TPCD) as oxidant or alkynes 12 to give 10, of which yields were from moderate to high. By analogy, the reaction of PEG-supported quinolinium salt 3 with 12 was to produce 9. However, in the presence of TPCD the reaction of 3 with 11 afforded indolizines 8, which was discovered firstly.

Preparation of new nitrogen-bridged heterocycles. 56. Syntheses and reactions of 1-[2,2-bis(alkylthio)-1-(ethoxycarbonylacetyl)vinyl]pyridinium salts

The title compounds, readily available from the S-alkylation of pyridinium 1-[alkylthio(thiocarbonyl)](ethoxycarbonylacetyl)methylides with alkyl halides or alkyl bromoacetates, were treated with a base and then a dehydrogenating agent to provide some unique products such as 3-[bis(alkylthio)methylene]-2(3H)-indolizinones and dialkyl 7-methyl-4-oxo-1,4,8,8a-tetrahydro-1,4-thiazino[3,4,5-cd]indolizine-1,5-dicarboxylates. On the other hand, similar reaction of these pyridinium salts in the absence of the dehydrogenating agent afforded alkyl 2-hydroxyindlizine-3-carboxythiolates, whose yields were increased by adding trifluoroacetic acid to the reaction mixture. The structures of some products were confirmed by the X-ray analyses.

Preparation of New Nitrogen-Bridged Heterocycles. 54. Increased Arene-Arene Interactions of 3-(Bicyclic and Tricyclic Arylmethylthio)thieno [3,4-b] indolizine Derivatives

Some thieno[3,4-b]indolizine derivatives having a 1-naphthylmethylthio, 2-methyl-1-naphthylmethylthio, 2-naphthylmethylthio, or 9-anthrylmethylthio group at the 3-position were prepared and their intramolecular arene-arene interactions were investigated. In comparison with 3-(methylthio)thieno[3,4-b]indolizines which have no such interactions, the (1)H-NMR spectra of title compounds showed large high-field shifts (delta 0.06-0.89 ppm) for the protons of the pyridine ring in the thieno[3,4-b]indolizine, and these values were considerably larger than those (delta <0.3 ppm) in 3-(benzylthio)thieno[3,4-b]indolizines. The UV spectra also exhibited a characteristic absorption band near 425 nm attributable to the arene-arene interaction. In the X-ray analyses of some compounds, however, the presence of both the gauche and the anti conformers at the sulfide spacer were confirmed.