Catalysis of enantioselective [2+1]-cycloaddition reactions of ethyl diazoacetate and terminal acetylenes using mixed-ligand complexes of the series Rh2(RCO2)n(L*4-n). Stereochemical heuristics for ligand exchange and catalyst synthesis.
This paper describes the synthesis of mixed Rh(2)(II) complexes containing bridging acetate and R,R-diphenyl-N-triflylimidazolidinone (DPTI) ligands (1, 2, and 9-19), and their function as enantioselective catalysts for the conversion of ethyl diazoacetate and terminal acetylenes to chiral cyclopropenes. Of these catalysts, 1 and 10 functioned with the highest enantioselectivity, in accord with a mechanistic model in which one of the ligand bridges is broken in the intermediate Rh-carbene complex. The synthetic results allow conclusions with regard to kinetically and thermodynamically favored pathways for the synthesis of mixed acetate-DPTI complexes. A new C(2)-symmetric complex having only two anti-DTBTI bridges (23) is shown to be a highly effective chiral catalyst, as expected from the model.
Lou
Yan
Y
Department of Chemistry and Chemical Biology, Harvard University, Cambridge, MA 02138, USA.
Remarchuk
Travis P
TP
Corey
E J
EJ
D000085:Acetates / Q000138:chemical synthesis*; D000114:Acetylene / Q000031:analogs & derivatives* / Q000737:chemistry*; D002384:Catalysis; D003500:Cyclization; D003979:Diazonium Compounds / Q000737:chemistry*; D008024:Ligands; D008968:Molecular Conformation; D009942:Organometallic Compounds / Q000138:chemical synthesis / Q000737:chemistry; D012238:Rhodium / Q000737:chemistry*; D013237:Stereoisomerism
D000085:Acetates; D003979:Diazonium Compounds; D008024:Ligands; D009942:Organometallic Compounds; D012238:Rhodium; D000114:Acetylene