合成路线1

The benzoylation of 2-methylthiopyrrole (I) with N,N-dimethylbenzamide (II) by means of POCl3 in refluxing CH2Cl2 gives 5-benzoyl-2-methylthiopyrrole (III), which is condensed with spiro[2.5]-5,7-dioxa-6,6-dimethyloctane-4,8-dione (IV) by means of NaH in DMF yielding compound (V). The oxidation of (V) with m-chloroperbenzoic acid in CH2Cl2 affords the sulfone (VI), which is submitted to methanolysis with methanol and HCl giving 1-(3,3-dimethoxycarbonylpropyl)-2-methanesulfonyl-5-benzoylpyrrole (VII). The cyclization of (VII) with NaH in DMF yields dimethyl 5-benzoyl-1,2-dihydro-3H-pyrrolo[1,2-a]pyrrole-1,1-dicarboxylate (VIII), which is finally hydrolyzed and decarboxylated with KOH in refluxing methanol. Compound (III) can be oxidized with m-chloroperbenzoic acid as before giving 2-methanesulfonyl-5-benzoylpyrrole (IX), which is then condensed with spiro compound (IV) as before to afford compound (VI), already obtained.