Mahatthananchai Jessada, Kaeobamrung Juthanat, Bode Jeffrey W
Laboratorium für Organische Chemie, Department of Chemistry and Applied Biosciences, Swiss Federal Institute of Technology (ETH) Zürich, Wolfgang Pauli Strasse 10, 8093 Zürich, Switzerland.
ACS Catal. 2012;2(2):494-503. doi: 10.1021/cs300020t. Epub 2012 Feb 29.
A combination of a chiral N-heterocyclic carbene catalyst and α,β-unsaturated aldehyde leads to a catalytically generated α,β-unsaturated acyl azolium, which participates in a highly enantioselective annulation to give dihydropyranone products. This full account of our investigations into the scope and mechanism of this reaction reveals the critical role of both the type and substitution pattern of the chiral triazolium precatalyst in inducing and controlling the stereochemistry. In an effort to explain why stable enols such as naphthol, kojic acid, and dicarbonyl are uniquely efficient, we have postulated that this annulation occurs via a Coates-Claisen rearrangement that invokes the formation of a hemiacetal prior to a sigmatropic rearrangement. Detailed kinetic investigations of the catalytic annulation are consistent with this mechanistic postulate.
手性 N - 杂环卡宾催化剂与 α,β - 不饱和醛的组合会生成催化产生的 α,β - 不饱和酰基唑鎓，其参与高度对映选择性环化反应生成二氢吡喃酮产物。我们对该反应的范围和机理的全面研究表明，手性三唑鎓预催化剂的类型和取代模式在诱导和控制立体化学方面起着关键作用。为了解释为什么诸如萘酚、曲酸和二羰基等稳定烯醇具有独特的高效性，我们推测这种环化反应是通过科茨 - 克莱森重排发生的，该重排涉及在 [3,3] - 迁移重排之前形成半缩醛。催化环化反应的详细动力学研究与这一机理假设一致。
