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。