Pyrans and their Benzo Derivatives - Synthesis

Diels-Alder reactions of fused pyran-2-ones with maleimides: efficient syntheses of benz[e]isoindoles and related systems.

Pyrano[3,4-b]indol-3-ones are shown to undergo cycloaddition with electron-rich olefins. However, after loss of CO2 from the adducts, the intermediate indole-2,3-quindodimethanes are not dehydrogenated—after a 1,5-sigmatropic hydrogen shift—to yield the expected heterosubstituted carbazoles. Rather, aromatisation arising from elimination of the hetero substituent takes place and other carbazoles are formed. In the same way, a hydroxyethylated naphthalenic compound was obtained from the adduct of 6,7-dimethoxy-1-methyl-2-benzopyran-3-one with 3,4-dihydrofuran. The hetero substituent is only conserved in cycloadditions of enamides with pyrano[3,4-b]indol-3-ones

Diels–Alder reactions of pyrano[3,4-b]indol-3-ones and a 2-benzopyran-3-one with hetero substituted olefins: generation of carbazole and naphthalene derivatives by elimination instead of dehydrogenation

Benzobicyclooctane compounds, their use in inhibiting cellular events involving TNF-α and IL-8, and in the treatment of inflammation events in general; a combinatorial library of diverse bicyclooctanes and process for their synthesis as a library and as individual compounds.

Pharmaceutical uses and synthesis of benzobicyclooctanes

The intramolecular ionic Diels−Alder reaction of α-acetylenic acetals as a precursor of the propargyl cation has been investigated in the presence of Lewis acids and in protic acids. The reaction of diene-tethered α-acetylenic acetals (1−2) with formic acid yielded the regioselective intramolecular ionic Diels−Alder reaction products, bicyclodienal (9) and bicyclodienone (11) derivatives, in good yields.

Intramolecular Ionic Diels−Alder Reactions of α-Acetylenic Acetals

The generation of methoxy-substituted 3H-2-benzopyran-3-ones from o-acylphenylacetic acid derivatives in acetic anhydride at 140 °C and their in situ Diets–Alder reactions being inefficient in the synthesis of some carbocyclic compounds, alternative reagents have been used. It is shown that, e.g. 1,3-dicyclohexylcarbodiimide (DCC) with 2-hydroxypyridine, disuccinimidyl carbonate (DSC), 2-ethoxy-N-ethoxycarbonyl-1,2-dihydroquinoline (EEDQ) of 2-isobutoxy-N-isobutoxycarbonyl-1,2-dihydroquinoline (IIDQ) are much more efficient reagents.Using these alternative reagents the formation of side-products from the benzopyranone, e.g. chrysene, can be avoided; with the modified DCC-method the 6,7-dimethoxy-1 -methyl-2-benzopyran3-one intermediate 8a can be identified spectroscopically. An exemplified procedure with IIDQ is proposed, opening new prespectives for Diets–Alder reactions of unstable or less reactive dienophiles with problematic benzopyranones.

Smooth generation of 3H-2-benzopyran-3-ones and their Diels–Alder reactions with olefinic dienophiles

La pyrolyse des adduits benzopyrannone-indenone, s'effectuant probablement via des o-quinodimethanes, donne des nor-C homo-D steroides, benzo [c] fluorenones et des traces de benzo [b] cyclopropa [lm] fluorenones

Eric G. Kiekens

Papers

Smooth generation of 3H-2-benzopyran-3-ones and their Diels–Alder reactions with olefinic dienophiles

Thermolysis of benzopyranone-indenone adducts. 2. Some new aspects of the mechanism

Smooth Generation of 3H‐2‐Benzopyran‐3‐ones and Their Diels‐Alder Reactions with Olefinic Dienophiles.