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Please login to access the full content or check if you have access via Method 3: From ortho-Substituted Nitroarenes; Bartoli Synthesis

DOI: 10.1055/sos-SD-110-00001

Joule, J. A.Science of Synthesis Knowledge Updates, (2010246.

In an extraordinary, but nonetheless efficient and certainly practically simple process, ortho-substituted nitroarenes 161 react with 3 equivalents of vinylmagnesium bromide to give 7-substituted indoles 162 (Scheme 57); see also Table 2.[‌196‌‌198‌] Better yields are obtained from nitroarenes which have larger ortho substituents and virtually no indole is produced if there is no ortho substituent.[‌197‌,‌198‌] The use of prop-1-enyl-, allyl-, and 2-styrylmagnesium bromides produces the corresponding 3-methyl-, 2-methyl-, and 3-phenyl-1H-indoles.[‌199‌] The use of 6 molar equivalents of the Grignard reagent in a mixture of diglyme and dimethoxyethane has been advocated for more efficient Bartoli reaction.[‌200‌] The Bartoli 1H-indole synthesis has been conducted on solid support, by linking substituted nitrobenzoic acids through the carboxylic acid group to Merrifield resin; there is the usual pattern of poorer yields (for example making 7-fluoro-1H-indoles) from substrates with smaller substituents ortho to the nitro group.[‌201‌]

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