Homogeneous, Supramolecular and Bio-Inspired Catalysis (HomKat) group, Van 't Hoff Institute for Molecular Sciences (HIMS), University of Amsterdam, Science Park 904, 1098 XH Amsterdam, The Netherlands.
Department of Bioorganic Synthesis, Leiden Institute of Chemistry, Leiden University, Einsteinweg 55, 2333 CC Leiden, The Netherlands.
J Am Chem Soc. 2021 Dec 8;143(48):20501-20512. doi: 10.1021/jacs.1c10927. Epub 2021 Nov 21.
The metallo-radical activation of -allylcarbonyl-aryl -arylsulfonylhydrazones with the paramagnetic cobalt(II) porphyrin catalyst [Co(TPP)] (TPP = tetraphenylporphyrin) provides an efficient and powerful method for the synthesis of novel 8-membered heterocyclic enol ethers. The synthetic protocol is versatile and practical and enables the synthesis of a wide range of unique 1-2-benzoxocins in high yields. The catalytic cyclization reactions proceed with excellent chemoselectivities, have a high functional group tolerance, and provide several opportunities for the synthesis of new bioactive compounds. The reactions are shown to proceed via cobalt(III)-carbene radical intermediates, which are involved in intramolecular hydrogen transfer (HAT) from the allylic position to the carbene radical, followed by a near-barrierless radical rebound step in the coordination sphere of cobalt. The proposed mechanism is supported by experimental observations, density functional theory (DFT) calculations, and spin trapping experiments.
具有顺磁钴(II)卟啉催化剂 [Co(TPP)]（TPP = 四苯基卟啉）的 -烯丙基羰基-芳基-芳基磺酰腙的金属自由基活化提供了一种用于合成新型 8 元杂环烯醇醚的有效且强大的方法。该合成方案具有多功能性和实用性，能够以高产率合成广泛的独特 1-2-苯并恶嗪。催化环化反应具有极好的化学选择性、对官能团具有高耐受性，并为合成新的生物活性化合物提供了多种机会。反应被证明是通过钴(III)-卡宾自由基中间体进行的，该中间体涉及从烯丙基位置到卡宾自由基的分子内氢转移 (HAT)，然后在钴的配位球中进行近乎无势垒的自由基回弹步骤。该机理得到了实验观察、密度泛函理论（DFT）计算和自旋捕获实验的支持。
