S. Kotretsou, M. Georgiadis
Apr 1, 2000
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Influential Citations
11
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Journal
Organic Preparations and Procedures International
Abstract
2-Pyrones have attracted much attention as precursors for the synthesis of a variety of biologically important compounds such as solanopyrones,] coumarins,2 pheromones,' inhibitors of a-chymotrypsin," elastase' and HIV protease,6 while some of their derivatives display significant biological activities (antifungal, phytot~xic) .~ It is known that volatile compounds and among them 2-pyrones are produced during the Maillard reaction.x These pyrones modify the flavor/aroma in food as well as a toasted caramel aroma in the heated oak wood to be used in barrels for aging wine and brandy products.y 3or 5-Bromopyrones are ambiphilic dienes which have been used as chameleon-like precursors to the much more reactive 2-pyrones at the Diels-Alder cycloaddition. These bromopyrones are also key compounds for the total synthesis of vitamin D, derivatives."'." A variety of approaches has been employed for the preparation of 2-pyrones starting mainly from 3-butenoic acid,I2 4,s-epoxy3,4-diphenyl-2-cyclopentene1-one, I ' decarboxylation of coumalic acid," or via cycloaddition of 1 -methoxybuta1,3-diene.' Bromopyrones have recently been obtained starting from 2pyrones."' I ' This paper reports a procedure for the effective synthesis of 2-pyrones as well as bromopyrones starting with 2-hydroxy-pyran-3(6H)-ones. Our starting materials which are endowed with different functionalities have been used for a multitude of reactions.15 The reported procedure depending on the experimental conditions, may lead to 2-pyrones or bromopyrones. These products may be used as synthons for additional syntheses. The synthesis of the 2H-pyran-2-one (6a) and 6-methyl-2H-pyran-2-one (6b) is depicted in (Scheme I ). The starting materials 6-hydroxy-2H-pyran-3(6H)-one ( la) and 6hydroxy-2-methyl-2H-pyran-3(6H)-one ( lb) were easily prepared in 80% yield according to the literature.'" l 7 Compound 5a was used as a key intermediate to prepare the corresponding bromopyrones 8 and 10 as shown in (Scheme 2). The 'H-NMR spectrum of 8 is characterized by the absence of H-3 and decreased shielding at H-5 and H-4 due to the presence of bromine. On the