3. Soluble Metal Oxides 2459 3.1. Polyoxometalates 2459 3.2. Peroxotungstates 2459 3.3. Peroxomolybdates 2460 3.4. Methyltrioxorhenium 2461 3.5. Other Metal Oxides 2461 4. Metal Oxides Generated in Situ 2461 4.1. Selenium and Arsenic Compounds 2461 4.2. Simple Metal Salts 2462 5. Coordination Complexes 2463 5.1. Manganese Porphyrins 2463 5.2. Iron Porphyrins 2464 5.3. Manganese Salen Complexes 2466 5.4. 1,4,7-Triazacyclononane (TACN) Complexes 2466 5.5. Iron and Manganese Pyridyl-Amine Complexes 2468

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Metal-Catalyzed Epoxidations of Alkenes with Hydrogen Peroxide

Transition metal chemistry of cyclopropenes and cyclopropanes.

Photochemical reactions contribute in a significant way to the existing repertoire of carbon-carbon bond-forming reactions by allowing access to exceptional molecular structures that cannot be obtained by conventional means. In this Review, the most important photochemical transformations that have been employed in natural product synthesis are presented. Selected total syntheses are discussed as examples, with particular attention given to the photochemical key step and its stereoselectivity. The structural relationship between the photochemically generated molecule and the natural product is shown, and, where necessary, the consecutive reactions in the synthesis are illustrated and classified.

Photochemical reactions as key steps in natural product synthesis

α-Methylene-γ-butyrolactones [dihydro-3-methylene-2(3H)furanones] constitute an important group of natural products and possess wide-ranging biological activities. Progress in the synthesis of the heterocycle and the classification of the synthetic methods are not only of practical interest, but also fundamentally important as a current example for the construction of an unusual 1,4-functionality distance and an α-substituted acrylic ester moiety which is susceptible to nucleophilic attack.

Synthesis and Biological Activity of α‐Methylene‐γ‐butyrolactones

Stereocontrolled synthesis of tetrasubstituted olefins.

Volatile constituents of Eugenia uniflora leaf oil.

Commercial Labdanum oil contains more than 300 constituents. 186 compounds (154 from the neutral part, 32 from the acidic part), representing about 95% of the oil, were identified mainly by their NMR spectra. Typical for the Labdanum oil in the C15 to C20 region are aromadendrane (23%), cadinane (9%) and labdane (7%) derivatives, mostly oxidized. The main constituents in this region are ledene (92, 9.3%), allo-aromadendrene (86, 1.5%), 1,5-cis-aromadendr-9-ene (91, 1.4%), viridiflorol (112, 4.3%), 1,2-dehydroviridiflorol (104, 1.4%), ledol (116, 1.3%), palustrol (105, 1.2%), the new cubeban-11-ol (113, 4.1%), copaborneol (117, 1.8%), and ambrox® (137, 1.4%). The following new natural compounds were isolated: 1. C9→C14compounds: 2,2,5-trimethyloxepan-4-one (30), cis-p-menth-4(8)-en-2-ol (40), (2E,4E)-6-hydroxy-2,6-dimethylhepta-2,4-dienal (59), cis-5-hydroxymentha-1(6),8-dien-2-one (71), 7-acetyl-2,2,6-trimethylbicyclo[4.2.0]octane (72), 4,4,7a-trimethyl-1,4,5,6,7,7a-hexahydro-2H-inden-2-one (83), 6-acetyl-5,8,8-trimethylbicyclo[3.2.1]octan-2,3-dione (119), 1,1,5,6-tetramethyl-1,2-dihydro- (89) and 1,1,5,6-tetramethyl-1,2,3,4-tetrahydronaphthalene (95). 2. Sesquiterpenes: cubeb-11-ene (82), 1,2-dehydroglobulol (106), 1-epi-3,4-dehydroviridiflorol (110), 3,4-dehydroglobulol (118), muurola-4,10(14)-dien-1-ol (120), 5-epi- (130) and 1,10-seco-aromadendran-1,10-dione (132), 5,11-epoxycadin-1(10)-en-9-ol (136), 10-hydroxycalamenene-8,9-epoxide (140) as well as 9(10→1)-abeo-9-hydroxy-aromadendran-10-one (131) named by us as 9-hydroxy-ladanifer-10-one, possessing a new skeleton. 3. Labdane derivatives: 7- (145), 8- (143) and 8(17)-15-nor-labdene (142). 4. From the acidic part: 3-isobutenyl-5-methyl-5-vinylbutyrolactone (M21), dimethyl (Z)-2-n-hexyl-3-methylbutendioate (M24) and the two epimers of methyl 1,5,5-trimethylbicyclo[4.1.0] heptan-7-carboxylate (M16, M,17). © 1998 John Wiley & Sons, Ltd.

Constituents of commercial Labdanum oil

155 constituents in the neutral part of commercial Haitian vetiver oil were identified. Their structures were assigned mainly by 1H- and 13C-NMR spectra, as reported previously. Furthermore, the following new compounds are described: acora-2,4-diene (7) and its 10-epimer (8), 3-isopropyl-2-(3-methylcyclopent-2-enyl)-tetrahydrofuran (4), 3-isopropyl-6-methyl-2-(3-methylcyclopent-2-enyl)-3,4-dihydro-2H-pyran (15) and its precursor 6-hydroxy-3-isopropyl-6-methyl-2-(3-methycyclopent-2-enyl)-3,4,5,6-tetrahydr-2H-opyran (D), 12,13-di-nor-6(7←8)-abeo-eremophil-1(10)-en-7-one (16), 8α-methyl-11,12,13-tri-nor-eremophil-1(10)-en-7-one (20), eudesma-5,7-dien-4-ol (cascarilladienol, 50), 13-nor-7,8-epoxy-eremophil-1(10)-en-11-one (98), eremophil-7(11)-en-10β-ol (111), 7,11-epoxy-eremophila-1,9-dien-8α-ol (124), two epimers of 6,12;7,11-diepoxy-eudesm-4-ene (125, 128) and of 7,11;8,12-diepoxy-eremophil-9-ene (129, 137). NMR data of β-vetispirene (18), γ-amorphene (22), β-vetivenene (48), elema-1,3-dien-6α-ol (6-epi-shyobunol, 32), eudesm-4(15)-en-5β-ol (69), trans-eudesma-4(15),7-dien-12-yl formate (vetiselinenyl formate, 127), ziza-6(13)-en-12-yl acetate (142), preziza-7(15)-en-12-yl acetate (143), methyl (E)-eremophila-1(10),7(11)-dien-12-oate (139) and (E)-eremophila-1(10),7(11)-dien-12-yl (isovalencenyl acetate, 144) are described. The contribution of some constituents to the very complex odour of vetiver oil is discussed. Copyright © 2000 John Wiley & Sons, Ltd.

Constituents of Haitian vetiver oil.

The essential oil of Hypericum perforatum L. of North Indian origin consists of 74% of monoterpene hydrocarbons, 7% of oxygenated monoterpenes, 10% of sesquiterpene hydrocarbons and only 1.5% of oxygenated sesquiterpenes. Ishwarane and α-cuprenene were isolated (besides some well-known monoterpene acetates and other sesquiterpenes) from the high boiling fraction of the oil. The low boiling fraction contained 5- and 6-methylheptan-2,4-dione as trace consistuents, while from the residue two new dimethylchromene derivatives 7-sec-butyl- and 7-isobutyl-2,2-dimethyl-2H,5H-pyrano[4,3-b]pyran-5-one were isolated.

Constituents of the leaf essential oil of Hypericum perforatum L. from India

The essential oil of the aerial parts of Artemisia sieberi Bess, has been investigated by a combination of chromatographic and spectroscopic methods. This oil possesses a fresh herbaceous, camphoraceous, earthy odour with a fruity and dried plum-like background. The main constituents of the essential oil are camphor (44%), 1,8-cineole (19%), camphene (5%), terpinen-4-ol (2.5%), α-terpineol (2%). The major component of the sesquiterpenes (altogether only 4.5% of the oil) is dehydro-1,8-sesquicineole.

Peter Weyerstahl

Papers

Volatile constituents of Eugenia uniflora leaf oil.

Constituents of commercial Labdanum oil

Constituents of Haitian vetiver oil.

Constituents of the leaf essential oil of Hypericum perforatum L. from India

The essential oil of Artemisia sieberi Bess.