Stereo- and regiochemistry in the (asymmetric) cycloaddition reaction of 5-chloro-2(1 H )-pyrazinones with cyclic and monosubstituted alkenes and with a N -acryloyl substituted chiral auxiliary
The cycloaddition of 5-chloro-2(1H)-pyrazinones 1 with various dienophiles was used to generate the corresponding 2,5-diazabicyclo[2.2.2]octanes. Following reduction or hydrolysis of the bridged adducts, the regio- and stereochemical structure was determined by analysis of the coupling and NOE patterns in the 1H NMR spectra. With symmetric dienophiles the endo adducts are formed exclusively. The regiochemistry
5-氯-2(1 H)-吡嗪酮1与各种亲二烯体的环加成反应用于生成相应的2,5-二氮杂双环[2.2.2]辛烷。桥联加合物还原或水解后,通过分析1 H NMR光谱中的偶联和NOE图谱确定区域和立体化学结构。对于对称的双亲二烯体,仅形成内加合物。1与丙烯酸甲酯和乙基乙烯基醚反应的区域化学,以及N-丙烯酰基取代的手性助剂(4 S)-4-异丙基-1-甲基四氢-2 H的不对称诱导-咪唑-2-酮在很大程度上取决于1的3个取代基的给电子或吸引性质和大小。
Generation of specifically substituted pyridines and pyridones from 2(1h) pyrazinones and acetylenes : A FMO description
The title compounds were obtained from reaction of variously substituted 2(1H)pyrazinones with acetylenic derivatives. Experimental evidence points out to a two step mechanism : a DielsAlder cycloaddition followed by immediate decomposition of the adducts into the title products via two competitive retro DielsAlderreactions. The product distribution, which is shown to be highly dependent on the