Abstract
2,3-Dihydro-5-hydroxy-6-methyl-4H-pyran-one [I] has been identified as a new cigarette smoke constituent. The concentration of substance I and of the homologous compound 2,3-dihydro-3,5-dihydroxy-6-methyl-4H-pyran-4-one [II] - determined in the smoke of Oriental, Virginia and Burley leaf - varies according to the type of tobacco. The amounts of substance I are 26, 20 and 6 µg a cigarette in the smoke of Oriental, Virginia and Burley tobaccos, respectively. For compound II the corresponding figures are 11, 13 and 4 µg a cigarette. Substance I is a new flavour compound which has a caramel odour with fruity overtones. This is undoubtedly important for the aroma of tobacco smoke. However, the presence of dihydro-γ-pyrone I in tobacco smoke is of theoretical interest as well. It is a cyclic enolone and has a structure similar to that of maltol and the cyclopentenolones, which we identified in tobacco smoke some time ago. Based on the similarity of structures we want to put forward the working hypothesis that a majority of the aroma substances in tobacco smoke have the constitution of an alicyclic or O-heterocyclic enolone containing a carbonyl and a C-alkyl (methyl or ethyl) group.