Dipartimento di Chimica "U. Schiff", Università degli Studi di Firenze, Via della Lastruccia 13, Sesto Fiorentino (FI) 50019, Italy.
Department of Organic Chemistry I, University of the Basque Country, UPV-EHU, Manuel de Lardizabal 3, Donostia-San Sebastián 20018, Spain.
J Org Chem. 2022 May 6;87(9):6038-6051. doi: 10.1021/acs.joc.2c00296. Epub 2022 Apr 20.
Six- and seven-membered ring-fused, functionalized cyclopentadienes can be obtained in moderate to excellent yields by a cascade process entailing the Au(I)-catalyzed propargyl Claisen rearrangement/Nazarov cyclization of propargyl vinyl ethers, the hetero-Diels-Alder reaction with dialkylazodicarboxylates, and the spontaneous conversion of cycloaddition products into cyclopentadienes by a highly regioselective cleavage of a C-N bond. Depending on the treatment of the crude reaction mixtures, two types of products can be obtained: cyclopentadienes with pendant hydrazine and aldehyde moieties that intramolecularly react to form hemiaminals are obtained in 43-52% overall yields when the crude reaction mixtures are left over KCO in a DCM solution. Instead, by reducing the aldehyde group just after addition of the heterodienophile, the regioselective C-N bond cleavage generates the corresponding cyclopentadienes bearing a hydrazine and an alcohol appendage in excellent yields (66-82%) over four steps, all in one pot. Two examples from the latter class of compounds were also converted into ring-fused, functionalized cyclopentadienes, bearing a protected amino group, by the selective N-N cleavage of the hydrazine moiety.
六元和七元环稠合、官能化的环戊二烯可以通过级联过程以中等至优异的收率得到，该过程包括 Au(I)催化的炔丙基乙烯基醚的丙炔基 Claisen 重排/Nazarov 环化、与二烷基叠氮二甲酸酯的杂 Diels-Alder 反应，以及通过高度区域选择性的 C-N 键断裂将环加成产物自发转化为环戊二烯。根据粗反应混合物的处理方式，可以得到两种类型的产物：当粗反应混合物在 DCM 溶液中留下 KCO 时，可获得带有侧链腙和醛基的环戊二烯，总收率为 43-52%，这些产物通过分子内反应形成半缩醛。相反，通过在添加杂二烯亲核试剂后立即还原醛基，区域选择性的 C-N 键断裂以优异的收率（66-82%）生成相应的带有腙和醇侧基的环戊二烯，该过程在一锅法中可进行四步反应。后一类化合物中的两个实例也通过选择性的 N-N 断裂腙部分转化为带有保护氨基的稠合、官能化的环戊二烯。
