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Selectivities of multicomponent [4 + 2]/[3 + 2] cycloadditions of 3-nitroindole with substituted alkenes: a DFT analysis.

The Journal of organic chemistry (2013-08-07)
Hélène Gérard, Isabelle Chataigner
ABSTRACT

The chemo-, regio-, and stereoselectivities of multicomponent [4 + 2]/[3 + 2] domino cycloaddition reactions involving nitroindole derivatives with vinylethers and acrylates are studied computationnally and compared to experimental results. In this process, the nitroarene first reacts as an electron-deficient heterodiene with the electron-rich alkene following an inverse electron-demand [4 + 2] process, leading to a nitronate intermediate in a fully selective way. This intermediate exclusively interacts, in a second step, with the electron-deficient alkene and undergoes a chemo- and regioselective [3 + 2] cycloaddition. The density functional theory calculations reported in this Article fully account for the selectivities observed experimentally. Electronic displacements along the reaction path are examined using a topological analysis of the electron-localization function (ELF). The first [4 + 2] reaction follows a classical concerted, although asynchronous process, which is reliably described by the frontier molecular-orbital (FMO) model. In contrast, the electronic displacements observed during the second [3 + 2] step are unexpected, involving an electron donation by the electron-deficient reaction partner.

MATERIALS
Product Number
Brand
Product Description

Supelco
Indole, analytical standard
Supelco
Indole solution, 2000 μg/mL in methanol, certified reference material
Sigma-Aldrich
Indole, ≥99%
Sigma-Aldrich
Indole, ≥99%, FG