Abstract
AbstractEnantiomerically pure bis‐heterocycles containing a (S)‐proline moiety have been prepared starting from (S)‐N‐benzylprolinehydrazide (2b). The reactions with isothiocyanates or butyl isocyanate in refluxing MeOH led to the corresponding thiosemicarbazide 5 and semicarbazide 9 with a N‐benzylprolinoyl residue. The structure of the tert‐butyl derivative 5d was established by X‐ray crystallography. Base‐catalyzed cyclization of 5 and 9 led to (S)‐3‐(pyrrolidin‐2‐yl)‐1H‐1,2,4‐triazole‐5(4H)‐thiones 6 and the corresponding 5(4H)‐one 8, respectively, whereas, in concentrated H2SO4, compounds 5 undergo cyclization to give (S)‐5‐amino‐2‐(pyrrolidin‐2‐yl)‐1,3,4‐thiadiazoles 7. Furthermore, 2b reacted with hexane‐2,5‐dione in boiling iPrOH to yield the (S)‐N‐(2,5‐dimethylpyrrol‐1‐yl)prolinamide 10. In the case of the bis‐heterocycle 8, treatment with HCOONH4 and Pd/C in MeOH gave the debenzylated product 12.
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