Reaction of 4-chlorocoumarin with organometallic reagents. Synthesis of trialkylbenzopyrans, 4-chlorobenzopyrans, 4-alkylcoumarins and o-hydroxyphenylprop-2-ynyl alcohols

Abstract

4-Chlorocoumarin has been shown to be a highly versatile starting material when treated with organometallic reagents. Thus, it has allowed the selective synthesis either directly, or through simple additional transformations, of 4-alkylcoumarins (with R₂CuLi in Et₂O, or PrⁱMgBr in THF), 2-chloro-2-(o-hydroxyphenyl)allyl alcohols or their 4-chloro-2H-1-benzopyran derivatives (with RMgX in THF), 2-(o-hydroxyphenyl)prop-2-ynyl alcohols (when non-acid hydrolysis were used in the latter reactions) and 2,2,4-trialkyl-2H-1-benzopyrans (when excess of RMgX or R₃Al reagents were used).