TANIS S. P.; RAGGON J. W., J. ORG. CHEM., 52,(1987) N 5, 819-827
作者:TANIS S. P.、 RAGGON J. W.
DOI:——
日期:——
Exploratory Studies on Reactions of Cobaloxime π-Cations with C-Nucleophiles: Irreversible Alkene Decomplexation versus Nucleophilic Capture
作者:Jennifer L. Gage、Bruce P. Branchaud
DOI:10.1021/jo951319i
日期:1996.1.1
(beta-Hydroxyalkyl)- and (beta-acetoxyalkyl)cobaloximes can undergo facile acid-catalyzed P-heteroatom exchange with oxygen and nitrogen nucleophiles in an S(N)1-like mechanism via cationic metal-alkene pi-complex intermediates (cobaloxime pi-cations). The reaction of cobaloxime pi-cations with carbon nucleophiles has not been previously reported. The results reported in this paper demonstrate that cobaloxime pi-cations are reasonably good electrophiles. They are sufficiently reactive to add to the electron-rich sp(2) centers in allyltrimethylsilane and pyrrole. A major side reaction for intermolecular reactions is irreversible alkene decomplexation. An intramolecular pyrrole cyclization (22 to 23, 83% yield) significantly raised the yield for nucleophilic addition compared to that of the analogous intermolecular couplings (12b tb 13b, 32% yield and 17 to 18, 29% yield). The results of these studies provide a foundation for the design and evaluation of modified cobalt ligands with the goal of suppressing alkene decomplexation and enhancing reaction of cobaloxime pi-cations with C-nucleophiles.
Pyrroles as terminators in cationic cyclizations. The preparation of 5,6,7,8-tetrahydroindolizidines and 6,7,8,9-tetrahydro-5H-pyrrolo[1,2-a]azepines