Acetylenes isocoumarin

Isocoumarins are less numerous than coumarins in nature. The acetylenic isocoumarin capillarin (225) is present in at least two Artemisia species and a fungus, Marasmius ramealis, produces 8-hydroxy-3-methylisocoumarin (226). 

A new acetylenic isocoumarin called 8-hydroxycapillarin [3-(but-2-ynyl)-8-hydroxyisocoumarin] has been isolated from Artemisia dracunculus ... 

Pyran-2-ones 796 can undergo Diels-Alder reaction with dimethyl acetylene dicarboxylate to afford dimethyl 3-methyl-isocoumarin-5,6-dicarboxylate in modest yield (Equation 330) <2003JOC1729>. 

Reaction Procedure (Scheme 2.158) Synthesis of isocoumarin. 2-Iodo-benzoic acid derivative (2.0 mmol) and CS2CO3 (4.0 mmol) were added to a vial containing anhydrous DMSO (8 mL), followed by addition of the appropriate acetylene derivative (2.2 mmol) and Cul (0.2 mmol). The suspension was stirred for 12 h at 100 °C. After cooling, the mixture was poured into the EtOAc (50 mL) and washed with water (2x25 mL) and brine (2x25 mL), then dried over Na2S04. Evaporation of the solvent under reduced pressure provided the crude product, which was purified by column chromatography (hexane-EtOAc, 20 1) or re-crystallized from hexane to afford the final product. 

In the Asteraceae, acetylenes are widely distributed and structurally very diverse, including aliphatic acetylenes, acetylenic thiophenes, aromatics, isocoumarins and spiroacetal enol ethers (Table 5.1 and Figures 5.3,5.4 and 5.5). 

Figure 5.4 Aromatic isocoumarin and spiroacetal enol ether acetylenes isolated from the utilized parts of food plants from the tribe Anthemideae (Asteraceae).

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