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The first synthesis of the sesquiterpene quinol dasyscyphin E has been achieved starting from cupressic acid. Key steps of the synthetic sequence are the oxidative degradation of the diterpene side chain to give a methylketone, the diastereoselective α-methylation of a protected ketoaldehyde, the subsequent intramolecular aldol condensation and the further Diels-Alder cycloaddition of a dienol ester.

α-Acetoxy aldehydes or α-acetoxy ketones can be efficiently synthesized by treating 2,3-epoxy primary alcohols with lead tetraacetate. The reaction, which proceeds with complete regio- and stereoselectivity facilitates the enantioselective synthesis of α-acetoxy carbonyl compounds from allyl alcohols, via Sharpless epoxidation. Cyclic β-hydroxy ethers, with an oxygenated five-, six- or seven-membered ring, are transformed into α-acetoxy ethers.

Efficient routes towards the austrodorane skeleton from the labdane diterpene (−)-sclareol (22) are described. The processes, based on pinacol rearrangement, take place with complete diastereoselectivity. Utilizing these, the marine nor-sesquiterpenes (+)-austrodoral (1) and (+)-austrodoric acid (2) have been prepared from 22. Ketone 19, a key intermediate in the synthesis of rearranged cytotoxic diterpene lactones, such as norrisolide (3), has also been prepared in moderate yield.

Two procedures to introduce an oxygenated function into the C-14 of abietane diterpenes with complete regioselectivity have been developed. Utilizing these, the synthesis of the antileishmanial quinone (−)-12-deoxyroyleanone (1) and a formal synthesis of antitumour and immunosuppressant (−)-triptonide (7) and (−)-triptolide (8) from (+)-abietic acid (13) have been carried out.

Methyl (8 R ,13 S )-8α,13:13,17-diepoxy-14,15-dinorlabdane-19-oate, easily prepared from communic acids, is a suitable intermediate for synthesizing pentacyclic quassinoids, because it enables the elaboration of the A ring and the further construction of the B–C–D ring system of these terpenoids. The cetal group is stable under the reaction conditions utilized during the elimination of the ester group and the introduction of the hydroxyl group on C-3. At the same time, it enables the regeneration of the methylketone and exocyclic double bond presented by methyl 13-oxo-14,15-dinorlabd-8(17)en-19-oate. The latter compound was previously used to construct the B–C–D-ring of these quassinoids.

Natural sesquiterpenes 5-(2′,5′-epoxy-2′,6′,6′-trimethyl)cyclohexyl-3-methyl-1-penten-3-ol (5), cis-3-[(E)-5′-hydroxy-3′-methyl-3′-pentenyl]-2,2-dimethyl-4-methylenecyclohexanol (elegansidiol) (6), 4-(5′-acetoxy-2′,6′,6′-trimethyl)cyclohex-2′-enyl-3-methyl-1-penten-3-ol (7) and 5-acetoxy-3-(3-hydroxy-3-methylpent-4-enyl)-2,4,4-trimethylcyclohex-2-enone (8) were prepared from 6,7-epoxygeranyl acetate (9), via (2′,5′-epoxy-2′,6′,6′-trimethyl)cyclohexylmethyl tosylate (10), for the first time. 5 is an intermediate in the synthesis of the sesquiterpene-coumarin ether (±)-farnesiferol C (1). The preparation of suitable intermediates for synthesising related natural farnesiferol B (3) and D (4) is also reported.

Two efficient enantiospecific syntheses of wiedendiol-A (1) from (−)-sclareol (7), via 11-bromo-8-drimene (11) and 8-drimen-11-al (3), are reported. The first enantiospecific synthesis of wiedendiol-B (2), via 8S,9S-driman-11-al (26), by two alternative routes starting from 7 and (+)-cis-abienol (8) is also described. 21 prepared from protocatechualdehyde (17) was used as aromatic synthon for preparing 1 and 2.

The synthesis of nor-ambreinolide (2) from cis-abienol (1) was carried out by direct treatment with OsO4-NaIO4 or RuO4-NaIO4. The oxymercuriation-demercuriation of 1 led to a mixture of 8,12-epoxylabdanes (5–17) which was also converted into nor-ambreinolide by treatment with RuO4-NaIO4. The formation pathways of such epoxy derivatives are discussed.

Efficient methods for preparing (±)-karahana ether (1b) and karahanaenine (2) from 6,7-epoxygeranyl acetate(3), by Lewis-acid-catalyzed electrophillic cyclization, are described.

Two routes for preparing Ambrox® (1) from the methyl esters of trans-communic acid (2b) and/or cis-communic acid (3b), via selective degradation of their side chains, stereoselective formation of the tetrahydrofurane ring, and reduction of the axial methoxycarbonyl group, are described.

Short and efficient syntheses of (−)-Ambrox® (12) from (−)-sclareol (1) and (+)-cis-abienol (11) are described. In constrast to previously described procedures, the transformation of 1 to 12, involving in the key step, an oxidative degradation by catalytic osmium tetroxide, in the presence of sodium periodate, has the advantage of using the more suitable sodium borohydride, as the reducing agent. The isolation and characterization of some reaction intermediates allowed us to confirm the degradation mechanism.

A mixture of the methyl esters of communic acids ( 3b, 4b, 5b ) was used in the synthesis of the ambergris-type odorants Ambrox ® ( 1 ) and ambracetal ( 2 ). Both syntheses involve methyl ketone 7 as the key intermediate.