Summary 5-Isopropyl-2-propyl-2-cyclohexen-l-one (1) and 5-isopropyl-2-(2-methylpropyl)-2-cyclohexen-1-one (2), homologues of the p-methene ketone carvotanacetone, have been identified in the oil of Anthemis nobilis. Their synthesis involved allylation of a cyclohexane-1,3-dione, and the acid-catalyzed cyclization to dihydrofurans of the 2-allylcyclohexane-l,3-diones is described. The stereochemistry of metal hydride reduction of 3-ethoxy-5-isopropyl-2-propyl-2-cyclohexen-1 -one (18) is mentioned in the course of the synthesis of the natural products. Some biogenetic considerations are discussed.In the course of an analysis of the oil of Roman camomile (Anthemis nobilis), the two ketones, 1 and 2, were isolated'). Because very small amounts were available from natural sources, we carried out syntheses of the racemates.In the first synthesis, we prepared 4-isopropyl-2-methoxy-2-cyclohexen-1-one (3) by the annelation method of Wenkert [2], and found the yields were poor, in accord with other workers [3]. We used the morpholine enamine 4 in place of the more expensive pyrrolidine enamine. The major difficulty of the route was in scale-up; while the removal of methanol from 1,4-dimethoxy-2-butanone (5) with p-toluenesulfonic acid runs well on the small scale described [2] [3], larger amounts tend to polymerize during the preparation. More rapid distillation results in lower yields, but the resulting mixture of 5 with the vinyl ketone 6 can be used as such in the cyclization to 3.Reaction of propylmagnesium bromide in ether on 3 yielded the corresponding tertiary alcohol 7, mostly in a single configuration which, we feel, must be the isomer having both alkyl substituents on the same side of the ring, based on the 'axial-attack' model for Grignard additions [4]. Treatment of the crude mixture of these alcohols with p-toluenesulfonic acid in refluxing toluene led to a 7: 1 -

SummaryP-Damascenone (1) has been identified in the fraction of Roman camomile (Anthemis nobilis) oil that contains homologues of carvotanacetone. 5-(3-Furyl)-2-methyl-1-penten-3-one (2), (E)-l-(2,6-dimethylphenyl)-2-buten-l-one (8), 4-isopropenylbenzaldehyde (4), were also identified and synthesized.

Kondensation von Allylbromid (Ia) bzw. Methallylchlorid (Ib) mit dem Hydroxyenon (II) gibt die Methylenalkyl‐Derivate (IIIa) bzw. (IIIb), die selektiv zu den Alkylcyclohexenonen (IVa) bzw. (IVb) hydriert werden.

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