Department of Chemistry, Aarhus University, Langelandsgade 140, 8000, Aarhus C, Denmark.
Angew Chem Int Ed Engl. 2018 Jan 26;57(5):1246-1250. doi: 10.1002/anie.201710694. Epub 2018 Jan 5.
The [8+2] cycloaddition of indene-2-carbaldehydes and nitro olefins is described to provide benzonorbornene scaffolds in a highly peri-, diastereo-, and enantioselective fashion in the presence of a C -symmetric aminocatalyst. This reaction, which proceeds through a transient semi-aromatic amino isobenzofulvene, represents the first example of catalytic formation and transformation of these species. Quantum chemical calculations suggest a kinetically controlled stepwise mechanism where the stereochemistry is determined in the first bond-forming event. Beyond the useful [8+2] cycloadducts, [10+4] cycloadducts have been identified in silico as potential off-pathway intermediates.
[8+2]环加成反应描述了在 C-对称的氨基催化剂存在下，茚-2-甲醛和硝基烯烃的反应，以高度区域选择性、立体选择性和对映选择性的方式提供苯并降冰片烯骨架。该反应通过瞬态半芳香族氨基异苯并呋喃进行，代表了这些物种的首次催化形成和转化的实例。量子化学计算表明，这是一个动力学控制的逐步反应机制，其中立体化学在第一个键形成事件中确定。除了有用的[8+2]环加成产物外，还在计算机中确定了[10+4]环加成产物作为潜在的非路径中间体。
