Zhang Y, Irshaidat T, Wang H, Waynant KV, Wang H, Herndon JW. Coupling of Fischer carbene complexes with conjugated enediynes featuring radical traps; Novel structure and reactivity features of chromium complexed arene diradical species.
J Organomet Chem 2008;
693:3337-3345. [PMID:
19838290 DOI:
10.1016/j.jorganchem.2008.08.003]
[Citation(s) in RCA: 12] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022]
Abstract
The reaction of Fischer carbene complexes with conjugated enediynes that feature a pendant alkene group has been examined. The reaction proceeds through carbene-alkyne coupling to generate an enyne-ketene intermediate. This intermediate then undergoes Moore cyclization to generate a chromium complexed arene diradical, which then undergoes cyclization with the pendant alkene group. The radical cyclization prefers the 6-endo mode unless radical-stabilizing groups are present to favor the 5-exo mode. The intermediate diradical species were evaluated computationally in both the singlet and triplet configurations. Arene triplet diradicals feature minimal spin density at oxygen and delocalization to chromium. The 6-endo cyclization product was kinetically and thermodynamically favored.
Collapse