Ch

"All measurements were performed at constant ionic strength (2.00 M using KNO3 as background electrolyte) and at pH 4.6-5.2.

bl0 mol % of Cu(N03)2; 17.5 mol % of ligand; conditions as outlined in Refs. 11 and 12.

cOnly the results for the major (>90%) endo isomer of the Diels-Alder adduct are shown.

d250 mol % of catalyst was used.

eJVa-Methyl-L-tryptophan.

Reactions Catalyzed

Figure 7.8 Reaction (1) catalyzed by Lewis acid Cu(II) and Ni(II) with ligands in Table 7.4.

Figure 7.8 Reaction (1) catalyzed by Lewis acid Cu(II) and Ni(II) with ligands in Table 7.4.

The mechanistic interpretation13 involves the interaction of a hydrophobic substituent in the ligand bound to Cu(II) with an aromatic ring in the dienophile exerting a favorable effect on the dienophile-Cu(II) interaction. Both the catalytic efficiency of Lewis-acid catalysis and the stereochemistry of the cycloaddition benefit from this water- induced interaction (Figure 7.9).

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