EXPLORATORY STUDIES ON REACTIONS OF COBALOXIME PI-CATIONS WITH C-NUCLEOPHILES - IRREVERSIBLE ALKENE DECOMPLEXATION VERSUS NUCLEOPHILIC CAPTURE

(beta-Hydroxyalkyl)- and (beta-acetoxyalkyl)cobaloximes can undergo fa cile acid-catalyzed P-heteroatom exchange with oxygen and nitrogen nuc leophiles in an S(N)1-like mechanism via cationic metal-alkene pi-comp lex 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-cati ons 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 irrever sible alkene decomplexation. An intramolecular pyrrole cyclization (22 to 23, 83% yield) significantly raised the yield for nucleophilic add ition compared to that of the analogous intermolecular couplings (12b tb 13b, 32% yield and 17 to 18, 29% yield). The results of these studi es provide a foundation for the design and evaluation of modified coba lt ligands with the goal of suppressing alkene decomplexation and enha ncing reaction of cobaloxime pi-cations with C-nucleophiles.