Epoxy terpenes cyclize readily, by confinement within zeolite NaY, to form exomethylenic cyclohexanols as the major products. The selective monocyclization of 10,11-epoxyfarnesyl acetate within NaY provides a short and efficient biomimetic route to (+/-)-elengasidiol and (+/-)-farnesiferols B-D. [reaction: see text].

The dimeric metabolite acremine G was synthesized featuring a highly regioselective and stereoselective Diels-Alder reaction between a TBS-protected hydroquinone diene and a structurally related alkenyl quinone. The major endo [4 + 2] adduct slowly transforms to acremine G by the atmospheric air under the deprotection conditions (in situ generated HF).

A variety of epoxy polyene terpenes cyclize readily by confinement within zeolite NaY to form primarily products of monocyclization. The monocyclization pathway is highly predominant, irrespectively of the side chain of the epoxy terpene, while the monocyclic products possess regioselectively an exomethylenic double bond. The selective monocyclization in the case of epoxyfarnesyl acetate, epoxyfarnesylacetone or 2,3-epoxysqualene, provides a direct route to the synthesis of a variety of natural products, such as elengasidiol, farnesiferols B-D, achilleol A, camelliol C and to four farnesylacetonederived metabolites isolated from the brown algae Cystophora monoliformis. The optical rotation of achilleol A derived from the cyclization of (S)-2,3-epoxysqualene matches with that of the natural product, thus the absolute configuration of achilleol A was established as 1S,3R. From the mechanistic point of view, the NaY-promoted cyclization of 9,10-epoxygeranylacetone, selectively deuterium labelled at the C-10 methyl group, is > 97% stereoselective with respect to the topicity of the gem-dimethyl group. This result is in agreement with a concerted mechanism. Finally, we have proved through labelling experiments, for the first time, that the biomimetic transformation of epoxy polyene terpenes to 2,3,4-trimethylcyclohexanones upon acid catalysis is a highly stereoselective process. Thus, the less hindered gem-methyl group on the epoxide functionality becomes a-to the carbonyl in the final isomerized product.

Four members of the cordiaquinone family (cordiaquinones B, C, J, and K) were synthesized on the basis of a bioinspired scenario in five to six steps from trans, trans-farnesol. As key reactions we used the acid-catalyzed cyclization of a suitable epoxy terpenoid and a Diels-Alder reaction between a diene and benzoquinone. The relative stereochemistry of cordiaquinone C is opposite to that reported in the isolation paper and is in agreement with a plausible scenario for the biosynthesis of cordiaquinones from a common (E)-configurated naphthoquinone epoxide precursor. A fast and clean methodology for the synthesis of the naturally occurring (Z)-beta-farnesene from cis-nerolidol is also reported.

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