This review presents the phytochemical constituents of the genus Plectranthus reported up to 1999. Only a tetrameric derivative of caffeic acid was isolated from P. japonicus, but a group of long-chain alkylphenols, of possible taxonomic significance in the genus, was also isolated. As a genus of the subfamily Nepetoideae, Plectranthus is free from iridoid glycosides and rich in essential oil (i.e. > 0.5% volatile oil on a dry weight basis). Diterpenoids are the more common secondary metabolites in Plectranthus. The majority of them are highly modified abietanoids. This seems to be similar to the pattern of diterpenoids observed for Salvia, but no clerodane diterpenoids were found in Plectranthus.

Fifteen ferrocene derivatives I-IX (four of which have been prepared for the first time: II, IIIf, V and VIII) have been prepared by Friedel-Crafts acetylation, Claisen condensation, Michael reaction, and ring closure by hydrazine hydrate. The anodic behaviour of these compounds has been studied by cyclic voltammetry at a platinum electrode in an aprotic solvent. All these substituted ferrocenes exhibit a reversible one-electron oxidation reduction centred at each iron centre, and the effect of substituents on the half-wave oxidation potential is discussed in terms of their electronic properties. Linear correlations have been observed between these potentials and the Hammett σ x constant for the substituents. Cyclic voltammetry has been carried out for ferrocene derivatives IIIa, V and IX.

Condensation of acetylacetone with 4‐methoxybenzaldehyde, 2,4‐dimethoxybenzaldehyde, 3,4‐dimethoxybenzaldehyde, 4‐nitrobenzaldehyde and 2,4‐dinitrobenzaldehyde in water and in the presence of cetyltrimethylammonium bromide (CTABr) as cationic surfactant in dilute sodium hydroxide at room temperature did not afford the expected arylideneacetylacetone but yielded 1H‐inden‐1‐one derivatives 1, while, with piperonaldehyde under the same conditions afforded dipiperonylideneacetone 2. Also 3‐acetylthiophene condensed with some aromatic aldehydes under the same conditions gave the expected stereoselective thienylpropenones 4. The structures of the products were identified by IR, NMR, Mass spectral data and elemental analysis.

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