Intramolecular Diels-Alder reactions of 2-(alkynyl)pyrimidines and 2-(alkynyl)pyridines
作者:A.E. Frissen、A.T.M. Marcelis、G. Geurtsen、D.A. de Bie、H.C. van der Plas
DOI:10.1016/s0040-4020(01)81093-0
日期:1989.1
Pyrimidines 3, 7 and 13 carrying an ω-alkynyl side-chain -CR2(CH2)nCH2CCH (R = H, CN; n = 1, 2) at the 2-position undergo intramolecular inverse electron demand Diels-Alder reactions across the C-2 and C-5 positions. Loss of hydrogen cyanide, caused by a retro-Diels-Alder reaction, from the intermediate cycloadducts leads to annelated pyridines 5, 9 and 15, respectively. Similarly, from the nitropyridines
嘧啶3,7和13携带ω -炔基侧链-CR 2(CH 2)Ñ CH 2 CCH(R = H,CN; n = 1时,2)在2位上进行分子内逆电子需求跨C-2和C-5位置的Diels-Alder反应。氰化氢的损失,通过逆狄尔斯-阿尔德反应引起的,从中间cycloadducts导致稠合吡啶5,9和15分别。类似地,由硝基吡啶16中的2,3-二氢硝基-1 H-茚18获得。讨论了电子效应和空间效应对环加成速率的影响。连接反应中心的链上的宝石二取代导致化合物3与13的速率显着提高。在二烯和亲二烯体之间的系链中具有额外亚甲基的化合物7,由于熵助的降低,其反应比化合物3慢得多。