Preparation of Substituted 2H-Pyrans via a Cascade Reaction from Methyl Coumalate and Activated Methylene Nucleophiles

Abstract

The reaction of methyl coumalate with a wide range of methylene active compounds, such as keto-esters or keto-sulfones and cyclic or acyclic diketones, afforded more than 30 2,3,5,6-tetrasubstituted 2H-pyrans. The reaction proceeds via a cascade reaction involving a Michael addition-6π-electrocyclic ring opening-proton transfer and 6π electrocyclization, in which a variety of functional groups were tolerated.

A Solvent‐free, Catalyst‐free Formal [3+3] Cycloaddition Dearomatization Strategy: Towards New Fluorophores for Biomolecules Labelling

“…The transformation starts by a formal Knoevenagel reaction, which implies a cascade of 1,6‐addition on MC, 6π‐electrocyclic opening, and 1,5‐proton shift, leading to the intermediate 1‐oxatriene. The final 6π‐electrocyclization gives the dihydropyrans (Scheme 1a) [15] . Additional advantage of using MC as a substrate lies in its biorenewable nature, which allows the reaction to run in an environmental‐friendly manner.…”

Recent Advances in the Synthesis of 2H-Pyrans

“…The condensation of methyl coumalate ( 40 ) with a wide range of active methylene compounds 41 has been implemented to access an extensive series of 2,3,5,6-tetrasubstituted 2HPs 42 (Scheme 15) [47]. The reaction involved a domino 1,6-Michael/6π-electrocyclic ring opening/[1,5]- H transfer/(decarboxylation)/6π-electrocyclization reaction.…”

Efficient Preparation of Methyl 2‐Oxo‐3‐aryl (heteroaryl)‐2H‐pyran‐5‐carboxylate via Pd‐Catalyzed Negishi Coupling

“…Therefore, beside involvement in cycloaddition reaction, [21–25] another feature related to the electron deficient conjugated diene moiety is its propensity to undergo 1,6 addition reactions with organometallic reagents followed by an opening electrocyclic reaction to give functionalized β,γ unsaturated carboxylic acids, [26] or α,γ dienoic acids [27] . In addition, reactions with soft nucleophiles such as β‐ketoesters, 1,3‐diketones, or amines allow access to 2H ‐pyrans, [28] aromatic compounds, [29] and pyridines, [30–31] respectively. To the best of our knowledge, the involvement of methyl coumalate in a cross‐vinylogous Rauhut‐Currier reaction [32] and in a Morita‐Baylis‐Hillman reaction [33] are the scarce examples of processes giving access to coumalate adducts.…”