Thia-Diels–Alder reactions of hetaryl thioketones with nonactivated 1,3-dienes leading to 3,6-dihydro-2H-pyrans: evidence for a diradical mechanism
作者:Grzegorz Mlostoń、Paulina Grzelak、Anthony Linden、Heinz Heimgartner
DOI:10.1007/s10593-017-2086-9
日期:2017.5
Dihetaryl thioketones possessing thiophen-2-yl and selenophen-2-yl rings react as “superdienophilic” reagents with nonactivated 1,3-dienes such as 2,3-dimethylbuta-1,3-diene, cyclopentadiene, and mixtures of isomeric hexa-2,4-dienes to produce the expected 2H-thiopyrans in moderate to excellent yields. In the latter case, the corresponding cis-2,2-dihetaryl-3,6-dimethyl-3,6-dihydro-2H-thiopyrans are
具有噻吩-2-基和硒代苯-2-基环的二杂芳基硫酮作为“超二亲”试剂与未活化的1,3-二烯,例如2,3-二甲基丁-1,3-二烯,环戊二烯和异构六-己基混合物2,4-二烯以中等至优异的产率产生预期的2 H-硫吡喃。在后一种情况下,相应的顺式-2,2-二杂芳基-3,6-二甲基-3,6-二氢-2 H-硫代吡喃形成了立体收敛的硫-狄尔斯-阿尔德反应的唯一产物。假定通过离域双基中间体的逐步机理来合理化所观察到的反应过程。m过量处理4,5-二甲基-2,2-二(噻吩-2-基)-3,6-二氢-2 H-噻喃室温下的-CPBA导致六元环中C = C键和硫原子的氧化。