Synthesis of 3-Allyl- and 3-Benzyl-D3-cephems through Sequential Reductive 1,2-Elimination/Addition/Cyclization of 3,4-Disubstituted 2-Butenoates in Allyl and Benzyl Halides/Mn/NiCl2/AlCl3/NMP Systems
摘要:
One-pot synthesis of 3-allyl- and 3-benzyl-Delta(3)-cephems through a sequential reductive 1,2-elimination/addition/cyclization of 3, 4-disubstituted 2-[2-oxo-3-phenylacetamido-4-(phenylsulfonylthio)azetidin-1-yl]-2-butenoates was successfully performed by treatment with allyl and benzyl halides in an Mn/NiCl2(bpy)/AlCl3/N-methyl-2-pyrroridinone (NMP) system.
Construction of cephem framework via sequential reductive 1,2-elimination–hydride addition in a tributyltin hydride–copper(I) chloride–NMP system: synthesis of 3-norcephalosporin
摘要:
A sequential reductive 1,2-elimination and hydride addition process for 3,4-disubstituted butenoates derived from penicillin is successfully performed with the aid of a combination of tributyltin hydride and copper(I) chloride in N-methyl-2-pyrrolidinone (NMP) to afford 3-norcephalosporin.
Synthesis of 3-norcephalosporin 1 was performed successfully by reaction of either 3-trifluoromethylsulfonyloxy-Δ3-cephem 2, allenecarboxylate 3 or 3,4-disubstitued but-2-enoates 4 with copper(I) chloride and tributyltin hydride in N-methylpyrrolidin-2-one (NMP). Generation and reactions of a copper(I) hydride species in the copper(I) chloride–tributyltin hydride–NMP or N,N-dimethylformamide (DMF)
Synthesis of 2-<i>exo</i>-Methylenepenam and 3-Chloro-Δ<sup>3</sup>-cephem through a Sequential Reductive 1,2-Elimination/S−S Bond Fission or Chloride Ion-Addition/Cyclization of 3,4-Disubstituted 2-Butenoates in Metal Salt/Metal Combinations
Synthesis of 2-exo-methylenepenam 1 through a sequential reductive 1,2-elimination/S-S bond fission/cyclization of 6 was performed by treatment with a PbBr2/Al (or a BiCl3/Al) combination in DMF, while that of 3-chloro-Delta(3)-cephem 2 through reductive 1,2-elimination/chloride ion-addition/cyclization was attained by use of an AlCl3/Al combination in N-methylpyrrolidone (NMP). The selective transformation of 6 to the allenecarboxylate 3 was also achieved by treatment with an AlBr3/Al combination in NMP. Cyclic voltammograms of 3,4-disubstituted 2-[2-oxo-3-(phenylacetamido)-4-[(phenylsulfonyl)thio]azetidin-1-yl]-2-butenoates (6) exhibit two irreversible reduction peaks responsible for reductive 1,2-elimination of the 3,4-disubstituted 2-butenoate moiety (at less negative potential) and for reductive S-S bond fission of the (phenylsulfonyl)thio moiety, suggesting that the reductive 1,2-elimination of 6 leading to allenecarboxylate 3 would occur prior to the reductive S-S bond cleavage.