Department of Chemistry, The University of Texas at San Antonio, One UTSA Circle, San Antonio, TX, 78249, USA.
Angew Chem Int Ed Engl. 2021 Aug 16;60(34):18484-18488. doi: 10.1002/anie.202105472. Epub 2021 Jul 14.
A general catalytic methodology for the synthesis of pyrazolines from α-diazo compounds and conjugated alkenes is reported. The direct hydrogen atom transfer (HAT) process of α-diazo compounds promoted by the tert-butylperoxy radical generates electrophilic diazomethyl radicals, thereby reversing the reactivity of the carbon atom attached with the diazo group. The regiocontrolled addition of diazomethyl radicals to carbon-carbon double bonds followed by intramolecular ring closure on the terminal diazo nitrogen and tautomerization affords a diverse set of pyrazolines in good yields with excellent regioselectivity. This strategy overcomes the limitations of electron-deficient alkenes in traditional dipolar [3+2]-cycloaddition of α-diazo compounds with alkenes. Furthermore, the straightforward formation of the diazomethyl radicals provides umpolung reactivity, thus opening new opportunities for the versatile transformations of diazo compounds.
本文报道了一种由α-重氮化合物和共轭烯烃合成吡唑啉的通用催化方法。叔丁过氧自由基促进的α-重氮化合物的直接氢原子转移（HAT）过程生成亲电的重氮甲基自由基，从而反转与重氮基团相连的碳原子的反应性。重氮甲基自由基区域选择性地加成到碳-碳双键，然后在末端重氮氮原子上进行分子内环化和互变异构，以优异的区域选择性得到一系列不同的吡唑啉，产率良好。该策略克服了传统的缺电子烯烃在α-重氮化合物与烯烃的二极[3+2]-环加成反应中的局限性。此外，重氮甲基自由基的直接形成提供了反转反应性，从而为重氮化合物的多功能转化开辟了新的机会。
