C,O-Dialkylation of Meldrum's Acid:  Synthesis and Reactivity of 1,3,7,7-Tetramethyl-4H,10H-6,8,9-trioxa-2-thiabenz[f]azulen-5-one

Abstract

Reaction of Meldrum's acid with 3,4-bis(chloromethyl)-2,5-dimethylthiophene (1) or 3,4-bis(bromomethyl)-2,5-dimethylthiophene (2) produces the kinetically favored C,O-dialkylation product, 1,3,7,7-tetramethyl-4H,10H-6,8,9-trioxa-2-thiabenz[f]azulen-5-one (4). Recrystallization of 4 from refluxing methanol results in the methanolysis product 5-(4-methoxymethyl-2,5-dimethylthiophen-3-ylmethyl)-2,2-dimethyl[1,3]dioxane-4,6-dione (5). Attempts to isomerize 4 to the thermodynamically favored C,C-dialkylation product, 1,3-dimethyl-5,6-dihydro-4H-cyclopenta[c]thiophene(2-spiro-5)2,2-dimethyl-4,6-dione (8), result in the formation of 1,3-dimethyl-7,8-dihydro-4H-thieno[3,4-c]oxepin-6-one (6). The transformation occurs via a retro-Diels-Alder elimination of acetone followed by hydrolysis and decarboxylation of the resulting ketene. The ketene is trapped by tert-butyl alcohol, furnishing 1,3-dimethyl-6-oxo-7,8-dihydro-4H,6H-thieno[3,4-c]oxepine-7-carboxylic acid tert-butyl ester (7). All compounds are characterized spectroscopically as well as by X-ray crystallography of products 4-7.

Meldrum's Acids as Acylating Agents in the Catalytic Intramolecular Friedel−Crafts Reaction

“…An inherent limitation of this strategy is the inability to C-alkylate (β,β-disubstituted)benzyl Meldrum's acid …”

Ruthenocene 1,2-Dicarboxylic Acid, Carboxylic Anhydride, and Acid Chloride: A Facile Route to Metallocene-Fused Acenequinones

“…Polycyclic aromatic hydrocarbons are benchmark semiconducting materials for organic field-effect transistors, light-emitting diodes, and photovoltaic cells. , Our long-term interest − in transition metal complexes of low-band-gap η 5 -cyclopenta[ c ]thienyl monomers and polymers led us to consider polyacenes with terminal cyclopentadienyl metal groups, which are unknown except for simple η 5 -indenyl complexes and a few benz[ f ]indenyl complexes of zirconium and ruthenium . We report here a route to metallocene-fused acenequinones, potential precursors for the desired acenes.…”

Sequential Rh(I)/Pd-Catalyzed 1,4-Addition/Intramolecular Allylation: Stereocontrolled Construction of γ-Butyrolactones and Cyclopropanes

“…1,4-Addition products 4 and 5 feature an enolizable Meldrum's acid moiety with, respectively, an appending allyl acetate and carbonate that can be activated by introduction of catalytic palladium. Further synthetic elaboration was envisaged in which Meldrum's acid, an ambident nucleophile, could trap the π-allylpalladium complex to lead directly and selectively to a vinyl γ-butyrolactone by O -alkylation or a vinylcyclopropane by C -alkylation. , …”