Synthesis of 4H-chromenes by silver (I)-catalyzed cycloaddition of ortho-quinone methides with N-allenamides

Advancements in the Preparation of 4H‐Chromenes: An Overview

“…As an extension of their previous work, [56] Jia and Xu utilized N ‐allenamides [57] as the electron‐rich partner, and realized a silver(I)‐catalyzed tandem [4+2]‐cycloaddition/isomerization between in situ generated o ‐QMs and N ‐allenamaides 220 for diverse synthesis of 4 H ‐chromenes 221 in good to excellent yields (Scheme 60). [58] …”

“…As an extension of their previous work, [56] Jia and Xu utilized N-allenamides [57] as the electron-rich partner, and realized a silver(I)-catalyzed tandem [4 + 2]-cycloaddition/isomerization between in situ generated o-QMs and N-allenamaides 220 for diverse synthesis of 4H-chromenes 221 in good to excellent yields (Scheme 60). [58] Two possible reaction pathways were put forward. In 2018, Anbarasan applied α-imino carbenoids, generated from N-sulfonyl-1,2,3-triazoles and Rh(II) catalyst, into the [4 + 2] formal cycloaddition with in situ generated o-QMs to afford substituted 4Hchromenes.…”

Dysprosium–balsalazide complex trapped between the functionalized halloysite and g‐C3N4: A novel heterogeneous catalyst for the synthesis of annulated chromenes in water

“…[63][64][65][66] Moreover, chromenes, as chemical intermediates, are broadly utilized in numerous industrial formulations including biological and pharmaceutical ones. [63,[67][68][69][70] It is worth mentioning that various approaches have been reported for the synthesis of chromenes. [64,69,71] One of the most relevant methods for the synthesis of the corresponding chromenes is the multicomponent reaction of aromatic aldehydes, malononitrile or ethyl cyanoacetate, and active methylene compounds, including 2-hydroxy-1,4-naphthoquinone, dimedone, and β-naphthol.…”

Controllable Synthesis of Two Isomers 4H-Chromene and 2,8-Dioxabicyclo[3.3.1]nonane Derivatives under Catalyst-Free Conditions

“…Thus far, methods for synthesizing 4 H -chromene or 2,8-dioxabicyclo[3.3.1]­nonane have been developed. Typically, phenols, ketones, propargynes, allenes, alkenes, 1,3-dicarbonyl compounds, and aryl bromides are used as substrates for the synthesis of 4 H -chromene. − The classical synthetic strategies for 2,8-dioxabicyclo[3.3.1]­nonane derivatives mostly involve a reaction between nucleophilic electrophiles with another substrate, typically 2-argiochroman-4-ol, 3-(argiocarbonyl)-2 H -chromen-2-one, acid ester compounds, 2-hydroxybenzaldehyde, phenols, 1,3-dicarbonyl compounds, and anthocyanin salt − (Figure ). Although these methods provide the basis for the synthesis of 4 H -chromene and 2,8-dioxabicyclo[3.3.1]­nonane, they exhibit some disadvantages, such as limited starting materials, the use of transition-metal catalysts, strong acids, and toxic and dangerous reagents or demanding reaction conditions and cumbersome post-treatment.…”