Abstract
Various thieno[3,4-b]indolizine derivatives having an allylthio or propargylthio group at the 3-position were prepared and their intramolecular arene–π interactions were investigated. Their 1H-NMR spectra showed significant low-field shifts (δ 0.10—0.34 ppm) to the 5-proton on the thieno[3,4-b]indolizine ring, and this effect was the reverse to that observed in 3-(arylmethylthio)thieno[3,4-b]indolizines. However, their UV spectra exhibited a characteristic absorption band due to the arene–π 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–π interactions are possible in one form and impossible in the other were confirmed by X-ray analyses of some compounds.
