82195-16-2Relevant academic research and scientific papers
NEW SUBSTITUTION REACTIONS ON INDOLE PROMOTED BY THE Cr(CO)3 UNIT
Semmelhack, M. F.,Wulff, W.,Garcia, J. L.
, p. C5 - C10 (2007/10/02)
Indole derivatives form complexes with the Cr(CO)3 unit at the 6-membered ring.Addition of reactive carbon nucleophiles occurs at the coordinated ring with strong preference for C-4 and, in a few cases, for C-7.Oxidation of the intermediate cyclohexadienyl anionic complexes produces substituted indoles in good yield.Complexes of N-methylindoline and benzofuran also undergo the addition/oxidation sequence preferentially at C-4.Changes in the substituents at C-3 and the nitrogen atom in the indole complexes influences the regioselectivity so that either C-4 or C-7 substitution can be observed.The selectivity is correlated with EHT calcualtions on free indole and complexes indole.
ADDITION OF CARBON NUCLEOPHILES TO ARENE-CHROMIUM COMPLEXES
Semmelhack, M.F.,Clark, G.R.,Garcia, J.L.,Harrison, J.J.,Thebtaranonth, Y.,et. al
, p. 3957 - 3965 (2007/10/02)
The electrophilic reactivity of arenes coordinated to the chromium tricarbonyl unit has been developed into several distinct methods for coupling carbon nucleophiles with aromatic rings.Addition of the nucleophile produces stable η-cyclohexadienyl chromium complexes which can be oxidized to induce loss of the endo hydrogen and the metal, overall nucleophilic substitution for hydrogen.Alternatively, the intermediate can be protonated and the resulting cyclohexa-1,3-diene can be detached from the chromium, effecting nucleophilic addition with reduction of one double bond.If a halogen (F, Cl) is present as a ring substituent, and if the nucleophile can migrate about the arene ligand, then loss of halide can occur parallel with classical nucleophilic aromatic substitution for halogen in electron-deficient haloarenes.With substituted arenes, the regioselectivity of addition becomes important and is often very high.Particularly useful are strong resonance donor substituents (RO-, R2N-, F-) where selectivity for meta attack is high.Indole provides an excellent example of selective activation, as the six-membered ring complexes selectively and is then susceptible to nucleophilic substitution, predominantly at the 4 and 7 positions.Substitution for halogen is a somewhat limited process and depends upon the nature of the nucleophile.Very reactive nucleophiles add to unsubstituted positions and are often slow to isomerize to the ipso position from which loss of halide can occur.
