R. Livingstone
2008
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ChemInform
Abstract
Publisher Summary This chapter focuses on the six-membered ring compounds with one hetero atom. Heterocyclic compounds consists a six-membered ring with one hetero atom. Pyridine is aromatic in character, which has five methine groups and a nitrogen atom. The pyrylium compounds are of special importance because pyrylium derivatives are found in natural pigments. Pyran and pyrylium derivatives are widely available in the carbohydrates, chromones, coumarins, flavones, anthocyanins, alkaloids and tocopherols. Pyrolysis of dihydropyran at 5000 gives ethylene (88%) and acrylic aldehyde (85%) thus, incidentally offering a convenient method for the preparation of the aldehyde. In the older literature compounds, heterocyclic ring are called chromenes and chromans, respectively. Now, these compounds are known as benzo[b]pyran and dihydrobenzo[b]-Pyran. Derivatives of benzo[b]pyran, 2H-chromene and dihydrobenzo[b]pyran, chroman occur widely in nature. Isoehroman, 3,4-dihydro- 1H-benzo[c]pyran (I) is prepared by the interaction of phenylethanol, trioxymethylene, and hydrochloric acid at about 00 or by the ring-closure of chloromethyl phenylethyl ether. Xanthene is the parent compound of a number of naturally occurring substances and some synthetic dyes are dibenzo[a,e]pyran. Xanthene derivatives have long been known, and include euxanthic acid and the related euxanthone.