Multicomponent synthesis of pyrano[2,3-c]coumarins

Abstract

A base-catalyzed, pseudo-four-component reaction of 4-hydroxycoumarin, two molecules of acetone, and amine towards the synthesis of pyrano[2,3-c]coumarins is reported.

4‐Hydroxycoumarin: A Versatile Substrate for Transition‐metal‐free Multicomponent Synthesis of Bioactive Heterocycles

“…The proposed mechanism for this reaction is depicted in Scheme ). [121] It is pertinent to note that this reaction requires a substantial amount (3.0 gm) of 3 Å molecular sieves. To obtain the generality of the reaction, various substituted 4-hydroxycoumarin and amines were tested.…”

“…Around the same time, Hsieh and co‐workers synthesized several amino‐substituted pyrans fused coumarin derivatives 123 in 70–79% yield via a pseudo‐four‐component reaction of 4‐hydroxycoumarin 61 , two molecules of acetone 121 , and several amines 122 in presence of Et 3 N as the base catalyst under reflux in acetone (Scheme 52). [121] It is pertinent to note that this reaction requires a substantial amount (3.0 gm) of 3 Å molecular sieves. To obtain the generality of the reaction, various substituted 4‐hydroxycoumarin and amines were tested.…”

Organocatalytic formal [3 + 3] cyclization of α-(6-indolyl) propargylic alcohols

“…1 Accordingly, many synthetic strategies have been developed based on the reaction of 4-hydroxycoumarins with diverse electrophiles such as α,β-unsaturated carbonyl compounds, 2 alkenes, 3 nitroalkenes, 4 MBH acetates, 5 and so on. 6 Moreover, C3-alkylation of 4-hydroxycoumarins with propargyl alcohols followed by intramolecular annulation has been developed towards pyranocoumarin-related products. 7 In particular, a Ca(OTf) 2 /Bu 4 NPF 4 mediated reaction of propargyl alcohols with 4-hydroxycoumarins was reported by Yaragorla et al towards pyrano[3,2- c ]chromen-5-ones (Scheme 1B).…”