Steroidal heterocycles: synthesis and structure of imidazo[2,1-b]thiazolo-, thiazolo[3,2-a]benzimidazolo-, and thiazolo[3,2-b]-s-triazolo-derivatives

Abstract

The condensation of 2α-bromo-5α-cholestan-3-one (1) with 2-mercaptoimidazole (2) in refluxing ethanol gave 5α-cholest-2-eno[2,3-b]-(imidazo[2,1-b]thiazole)(5) and 3β-ethoxy-2′β,3′-dihydro-5α-cholestano[2,3-b](imidazo[2,1-b]thiazole)(6), whereas the reaction of 2-mercaptoimidazole (2) with 16α-bromo-3-methoxyestra-1,3,5(10)-trien-17-one (7) gave the uncyclised product 16α-(imidazol-2-ylthio)-3-methoxyestra-1,3,5(10)trien-17-one (8). Under analogous reaction conditions, the condensation of 2-mercaptoimidazole (2), 2-mercaptobenzimidazole (12), 3-mercapto-1,2,4-triazole (35), and their derivatives with 2α-bromo-3-oxo-steroids gave the expected cyclised products. However, from the condensation reactions between 3-mercapto-1,2,4-triazoles (35) and (36) with the 16α-bromo-17-oxo steroid (7) only 17β-ethoxy-3-methoxy-5′,6′-dihydro [16,17-e]-(thiazolo-[3,2-b]-(s-triazole)(44) and its 2′-methyl derivative (45) were isolated. The structures of all the condensation products were determined with the help of i.r., ¹H n.m.r., and ¹³C n.m.r, spectroscopy.