Microwave irradiation in solvent-free conditions induces pyrazolyl 2-azadienes to undergo Diels-Alder cycloadditions with nitroalkenes within 5-10 min to give good yields of pyrazolo[3,4-b]pyridines. This is the first example of a [4 + 2] cycloaddition of a 2-azadiene involving a pryazole ring. By classical heating, these reactions do not occur or afford only traces of the products.
在无溶剂条件下,微波辐照可诱导 2-
叠氮吡唑在 5-10 分钟内与硝基烯发生 Diels-Alder 环加成反应,从而得到产率很高的
吡唑并[3,4-b]
吡啶。这是第一个涉及普莱唑环的 2-氮二烯 [4 + 2] 环加成反应实例。通过传统的加热方法,这些反应不会发生或只能得到微量的产物。