合成路线1

The reaction of D-asparagine (XXIV) with methyl trifluoroacetate (XXII) in methanol gives N-(trifluoroacetyl)-D-asparagine (XXV), which is esterified with MeOH and Ac-Cl, yielding the methyl ester (XXVI). The reaction of (XXVI) with TsCl and pyridine in dichloromethane affords the 3-cyanopropionic ester (XXVII), which is cyclized by hydrogenation over a Rh/Al2O3 catalyst in ethanol to provide the pyrrolidinone (XXVIII). Finally, this compound is condensed with benzyl chloroformate and BuLi in THF to furnish the target pyrrolidinone intermediate (XXIII). Assembly of the target compound: The reductive methylation of intermediate pyrrolidinone (XXIII) by means of LiBH4 in THF, followed by treatment with EtOH and conc. H2SO4, gives 2-ethoxy-3(R)-(trifluoroacetamido)pyrrolidine-1-carboxylic acid benzyl ester (XXIX), which is condensed with the intermediate silyl enol ether (XIII) by means of BF3/Et2O in dichloromethane to yield the adduct (XXX). The deprotection of the amino group of (XXX) with K2CO3 in ethanol/water yields the aminopyrrolidine (XXXI), which is cyclized by means of t-butylmagnesium bromide and TMEDA in THF to afford the bicyclic compound (XXXII). The reaction of the free NH group of (XXXII) with methanesulfonyl chloride and LiHMDS in THF provides the cyclic methanesulfonamide (XXXIII), which is decarboxylated by hydrogenation with H2 over Pd/C in dioxane/ethyl acetate to give the bipyrrolidine derivative (XXXIV). Finally, this compound is condensed with the oxazole intermediate (IX) by means of HOBT and DEC in acetonitrile.