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
Abstract An efficient one-pot three-component protocol for the synthesis of novel tetrahydrobenzofuran-chromone conjugates using 3-formylchromones and 1,3-cyclohexandiones in the presence of a variety of alkyl or aryl isocyanides was developed. The reaction sequence consists of an initial Knoevenagel condensation of aromatic aldehydes with 1,3-cyclohexandione derivatives, followed by a [4 + 1] cycloaddition