Does the DABCO-catalysed reaction of 2-hydroxybenzaldehydes with methyl acrylate follow a Baylis–Hillman pathway?

Abstract

Evidence is presented which supports the intermediacy of dipolar Baylis-Hillman-type adducts in the synthesis of coumarin and chromene derivatives from the reaction of 2-hydroxybenzaldehydes with methyl acrylate in the presence of 1,4-diazabicyclo[2.2.2]octane (DABCO).

Synthesis of 3-substituted 2-trifluoro(trichloro)methyl-2H-chromenes by reaction of salicylaldehydes with activated trihalomethyl alkenes

“…It is well known that the reactions of salicylaldehydes with acrylonitrile [27][28][29], alkyl vinyl ketones [30][31][32][33], and nitro alkenes [34][35][36][37][38][39] give 3 -chromenes containing electron-withdrawing substituents at the 3-position. Although these compounds are not found in nature, their derivatives are reported to be useful from industrial and medical points of view [40,41].…”

Synthesis of heterocyclic compounds using basic zeolite Csβ*

“…2-Acetyl-6-methyl-3,4-dihydro-2H-pyran (11). MVK (0.219 g, 3.13 mmol) was added to zeolite Csβ (0.047 g).…”

“…This compound was obtained previously in [5]. Various catalysts have been applied for the synthesis of chromenes and their derivatives, including complexes of palladium and ruthenium [6][7][8], secondary amines [9], cyclic diamines [10][11][12], and zeolites [13]. It is known that the interaction of salicylaldehyde derivatives with various α,β-unsaturated carbonyl compounds in the presence of basic catalysts proceeds as a tandem Michael oxareaction and aldol condensation [10,14] (Scheme 2).…”

Strong base- or acid-mediated chemoselectivity shifts in the synthesis of 2H-chromene or coumarin derivatives from common Baylis-Hillman adducts

“…14e16 Our interest in benzopyran chemistry has involved research on Baylis-Hillman reactions of 2-hydroxybenzaldehydes with ethyl-or methyl acrylatedreactions which afforded complex mixtures of coumarin and 2H-chromene derivatives (Path I, Scheme 1). 17,18 Cyclisation to form coumarins involves intramolecular acyl substitution by the phenolic hydroxyl group, and it was found that replacement of the ester function (R 1 ¼CO 2 Me/Et) in the activated alkene (2) by electron-withdrawing groups incapable of undergoing acyl substitution (R 1 ¼CN, COMe, SO 2 Ph, SO 3 Ph) resulted in the chemoselective formation of 3-substituted 2H-chromenes (3) via a conjugate-addition elimination pathway (Path II). 19,20 Chemoselective access to coumarins (6), on the other hand, was achieved, initially, using protection strategies (Path III).…”