Methyl alcohol trap, nucleophilic

In addition to alcohols, some other nucleophiles such as amines and carbon nucleophiles can be used to trap the acylpalladium intermediates. The o-viny-lidene-/j-lactam 30 is prepared by the carbonylation of the 4-benzylamino-2-alkynyl methyl carbonate derivative 29[16]. The reaction proceeds using TMPP, a cyclic phosphite, as a ligand. When the amino group is protected as the p-toluenesulfonamide, the reaction proceeds in the presence of potassium carbonate, and the f>-alkynyl-/J-lactam 31 is obtained by the isomerization of the allenyl (vinylidene) group to the less strained alkyne. 

One of the first notions of EGA-catalyzed reactions was the rationalization [8, 14] of the unexpected outcome of anodic oxidation of methyl arenes, (1), in MeGN containing various amounts of water. Preferentially A-benzyl acetamides, (3), rather than the benzyl alcohols, (2), were formed [15, 16] (with increasing amounts of water, increasing amounts of aldehyde was formed as a side product [16]). Since water is a more powerful nucleophile than MeCN, it is reasonable to believe that the carbocation formed by overall two-electron oxidation and deprotonation is initially trapped by water. However, the process is reversible in the presence of a strong EGA (protons liberated from the oxidized substrate), and the carbocation is eventually trapped by the excess MeCN, Scheme 1. 

Benzylic carbocations are also stabilized by complexation to chromium and a number of interesting reactions have been reported. Again, reaction of the carbocations with nucleophiles occurs from the exo face of the complex, relative to the metal. Carbocations are readily formed by treatment of benzylic alcohols with a strong acid, such as sulfuric acid, tetrafluoroboric acid, or borontrifluoride etherate. The cation can be trapped with water, alcohols, nitriles, and mono-or disubstituted amines to form alcohols, ethers, amides, and di- or trisubstituted amines respectively. Scheme 96 illustrates the formation of a benzylic carbocation followed by intramolecular trapping, resulting in a net inversion of stereochemistry. Benzylic acetates react with trimethyl aluminium introducing a methyl group from the opposite face of the metal. 

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