Notable Examples of Benzopyrylium and Benzopyrone Syntheses

The hrst synthesis of pelargonidin chloride used methyl ethers as protecting groups for the phenolic hydroxyls during the Grignard addition step.  

The scheme below shows two contrasting routes to apigenin. The modem use of excess of a very strong base, and the reaction of the resulting polyanion obviated the need for phenolic protection in one synthesis.  

An elegant and flexible strategy for the assembly of a synthon for the ort/to-hydroxyaryl-1,3-diketone required for a chromone synthesis depends on the use of an isoxazole as surrogate for the 1,3-diketone unit (25.7). An isoxazole was produced by the cycloaddition (25.12.1.2) of an aryl nitrile oxide to tri-n-butylstannylacetylene, the product coupled with 2,4,6-trihydroxyiodobenzene and then the N-0 bond hydrogenolytically cleaved.  

When salicylaldehyde and 2,3-dimethyl-l-benzopyrylium chloride are heated together in acid, a condensation product C18H15O2 Cl is formed. Treatment of the salt with a weak base (pyridine) generates a neutral compound, C18H14O2. Suggest stmctures for these two products. 

When ethyl 2-methylchromone-3-carboxylate is treated with NaOH, then HCl, a product C11H8O4 is produced that does not contain a carboxylic acid group, but does dissolve in dilute alkali suggest a stmcture and the means whereby it could be formed. 

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Notable examples of benzopyrylium and benzopyrone syntheses 9.3.7. / Pelargonidin chloride... 

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