Direct access to functionalized 4-nitromethyl-chromenes via a domino reaction under catalyst-free conditions

Abstract

A catalyst-free tandem reaction for synthesis of 4-nitromethyl-chromenes has been established from accessible α, βunsaturated ketones and CH3NO2. Target products were obtained in non-toxic solvent under catalyst-free conditions. Especially, the scope of substrates was expanded to tricyclic α, β-unsaturated ketones for the synthesis of tetracyclic heterocompounds in medium to good yields.

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

“…Zhang and Hu in 2015 reported a simple and practical method for the synthesis of such compounds in moderate yields under catalyst-free and non-toxic solvent conditions (H 2 O as solvent) (Scheme 21). [21] Compared to aforementioned reports, [19][20] light irridiation was not needed. It might indicate that two possible reaction pathways were involved, in which the initial formation of 2Hchromene hemiketal 11 a or Henry reaction product 82 was included in the generation of 4H-chromene 81 a.…”

“…Described above are the examples that employed pre ‐prepared 2 H ‐chromene hemiketals as the starting materials. In fact, under suitable conditions, 2‐hydroxychalcones can be used as the starting materials to in situ generate 2 H ‐chromene hemiketals which then undergo the C4‐nucleophilic substitution with nucleophiles to afford the C4‐functionalzied 4 H ‐chromenes [19–21] . In this way, the atom‐ and step‐economy have been improved greatly.…”

“…In fact, under suitable conditions, 2-hydroxychalcones can be used as the starting materials to in situ generate 2H-chromene hemiketals which then undergo the C4-nucleophilic substitution with nucleophiles to afford the C4-functionalzied 4Hchromenes. [19][20][21] In this way, the atom-and stepeconomy have been improved greatly. Normally, 2hydroxychalcones 67 goes through a UV or sunlight irradiated double-bond isomerization to deliver Zenone 68, which is converted into benzopyrylium 13 via dehydrative cyclization under the catalysis of Brønsted acids (Scheme 17).…”