this invention relates to indolizine compounds having formula in which r 1 is h , lower alkyl , lower alkoxy , oh , f , cl , br , i , no 2 , or cn ; r 2 is alkyl optionally substituted with lower alkoxy , oh , cn , f , cl , br , i , no 2 , nh 2 , cnh 2 , co 2 h , or co 2 r ′; or aryl optionally substituted with lower alkyl , lower alkoxy , oh , cn , f , cl , br , i , no 2 , nh 2 , or cnh 2 , co 2 h , or co 2 r ′; r 3 is h or lower alkyl ; r 4 is n - oxy pyridyl or pyridyl optionally substituted with f , cl , br , or i ; and x is c , n , o , s , s , s 2 , c , c — n , n — c , or deleted . each of r ′ and r ″, independently , is h , or alkyl optionally substituted with lower alkoxy , oh , cn , f , cl , br , i , no 2 , nh 2 , or cnh 2 .