Grignard reagents Bartoli indole synthesis

Invented merely 20 years ago in 1989, the Bartoli indole synthesis refers to the formation of 7-substituted indoles from the reaction of ort/io-substituted nitroarenes and excess of vinyl Grignard reagents. ... 

This reaction was first reported by Giuseppe Bartoli in 1989. It is the treatment of an 6>rf/z6>-substituted nitroarenes with 3 eq. of vinylmagnesium bromide to afford 7-substituted indole, and is generally known as the Bartoli indole synthesis. Currently, this reaction has rapidly become the shortest and most flexible approach for indoles with 7-substituents. In fact, this reaction is based on Bartoli s earlier work, in which he had extensively studied the reaction between nitroarenes and a lesser amount of Grignard reagents and found that aromatic nitroso compounds can be formed by using 2 eq. of vinylmagnesium bromide and nitroarenes. ... 

The mechanism for Bartoli indole synthesis is proposed as shown below, according to the fact that nitroso compounds may be generated from nitroarenes and 2 equivalents of Grignard reagents. ... 

The Bartoli-indole synthesis utilizes the [3,3]-rearrangement of an 0-vinyl-iV-arylhydroxylamine intermediate to form indoles through a similar rearrangement and condensation process as the Fischer-indole synthesis f Scheme 14.7a). The rearrangement precursor 59 is generated from the addition of a vinyl Grignard reagent to a nitroarene. The... 

Bartoli, G., Palmieri, G., Bosco, M., Dalpozzo, R. The reaction of vinyl Grignard reagents with 2-substituted nitroarenes a new approach to the synthesis of 7-substituted indoles. Tetrahedron Lett. 1989, 30, 2129-2132. 

Synthesis of ortho alkyl anilines (Rosini) by reductive C-alkylation of nitroarenes. Also synthesis of indoles (Bartoli) by reaction of 2-substituted nitroarenes with vinyl Grignard reagents. 

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