The alkylation and ring-expansion of chromones by diazoalkanes; reluctance of oxygen to engage in sigmatropic shifts
作者:Francis M. Dean、Robert S. Johnson
DOI:10.1039/p19810000224
日期:——
In general, chromones activated by electron-withdrawing groups at position 3 are alkylated (at position 2) by diazoalkanes in the same manner as the isomeric coumarins. For example, 6-methylchromone-3-carbonitrile (3a) is converted by diazoethane into 2-ethyl-6-methylchromone-3-carbonitrile (3c). 2-Diazopropane affords cyclopropane by-products as well, and a 3-formyl group usually suffers homologation
通常,在3位被吸电子基团活化的色酮以与异构香豆素相同的方式被重氮烷烃烷基化(在2位)。例如,通过重氮乙烷将6-甲基色酮-3-甲腈(3a)转化为2-乙基-6-甲基色酮-3-甲腈(3c)。2-重氮丙烷也可提供环丙烷副产物,并且3-甲酰基通常会与适当的酮发生同系化反应,就像2-重氮丙烷将3-甲酰基-6-甲基色酮转化为2-异丙基-6-甲基-3-(甲基丙酰基)色酮(8)。与香豆素化学形成鲜明对比的是,没有扩环成1-苯并氧杂庚酮系列。