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10.14.2.3.2 Method 2: Of Benzodiazepines

DOI: 10.1055/sos-SD-010-00811

Donohoe, T. J.Science of Synthesis, (200110670.

The ring contraction of various benzodiazepines is a useful method of isoindole formation. Early reports of this sequence pertained to the reaction of benzodiazepines 77 and 78 with acetic anhydride or (better) sodium hydride.[‌81‌,‌82‌] In a later report, 80 was shown to fragment to the isoindole 82 (in 85% yield) on reaction with methanol and then hydrochloric acid.[‌83‌] A mechanistic sequence that explains this transformation is shown in Scheme 19. Acidic hydrolysis of the imidate 80 gives a formamide 81, which is then presumed to cyclize (possibly via an oxonium ion) to form the 1H-isoindole 82.

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