Thiourea-catalyzed dearomatizing [4+2] cycloadditions of 3-nitroindole |
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Affiliation: | 1. Green Chemistry and Enabling Technologies, Institut des Biomolécules Max Mousseron, Université de Montpellier, France;2. School of Chemistry, University of Nottingham, UK |
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Abstract: | We have developed two efficient thiourea promoted dearomatizing processes involving the cycloadditions of 3-nitroindoles. The C2 C3 double bond of the heteroarene can be involved as electron-poor 2π dienophile in 4+2] cycloadditions. While the uncatalyzed process requires harsh conditions, the organocatalyzed reaction takes place at room temperature and atmospheric pressure. The C2 C3 N O motif of the heteroarene can also react as an electron-poor 4π heterodiene in 4+2] / 3+2] cycloadditions cascades, under high pressure. In contrast to Lewis acid activation, thiourea promotion thus proves efficient even under unconventional activation conditions and in the presence of acid sensitive reactants such as enol ethers. |
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