- Synthesis and Applications of Cyclohexenyl Halides Obtained by a Cationic Carbocyclisation Reaction
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The synthesis of cyclic alkenyl halides (mainly fluorides, chlorides and bromides) from alkynol or enyne derivatives by an acid-mediated cationic cyclisation reaction is disclosed. This high-yielding, scalable and technically simple method complements and challenges conventional methodologies. This study includes the development of biomimetic cationic cyclisation reactions of polyenyne derivatives to give interesting halogen-containing polycyclic compounds. The application of this reaction in the key step of the synthesis of two terpenes, namely austrodoral and pallescensin A, and the potent odorant 9-epi-Ambrox demonstrates the potential of the reaction for natural product synthesis.
- Alonso, Pedro,Pardo, Pilar,Fontaneda, Raquel,Fa?anás, Francisco J.,Rodríguez, Félix
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p. 13158 - 13163
(2017/09/06)
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- Diastereoselective Synthesis of (±)-Ambrox by Titanium(III)-Catalyzed Radical Tandem Cyclization
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A synthesis of (±)-ambrox, a compound with delicious ambergris-type scent, is presented. The key step is a highly diastereoselective titanocene(III)-catalyzed radical tandem cyclization of a farnesol derivative.
- Rosales, Antonio,Foley,Padial, Natalia M.,Muoz-Bascn, Juan,Sancho-Sanz, Iris,Roldan-Molina, Esther,Pozo-Morales, Laura,Iras-lvarez, Adriana,Rodrguez-Maecker, Roman,Rodrguez-Garca, Ignacio,Oltra, J. Enrique
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p. 369 - 374
(2016/02/09)
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- Scalable Synthesis of the Amber Odorant 9-epi-Ambrox through a Biomimetic Cationic Cyclization/Nucleophilic Bromination Reaction
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A novel biomimetic nucleophilic bromocyclization reaction is used in the key step of a new and straightforward synthesis of 9-epi-Ambrox, an organic compound of high interest and value in the context of fragrances. This strategic reaction allows access to 9-epi-Ambrox on a gram scale from a dienyne derivative, easily available from geraniol, following a sequence of seven steps (35% global yield) with just one purification process. Both enantiomers of the molecule were obtained by a challenging enzymatic resolution.
- Fontaneda, Raquel,Alonso, Pedro,Fa?anás, Francisco J.,Rodríguez, Félix
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supporting information
p. 4626 - 4629
(2016/09/28)
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- Synthesis of five-membered cyclic ethers by reaction of 1,4-diols with dimethyl carbonate
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The reaction of 1,4-diols with dimethyl carbonate in the presence of a base led to selective and high-yielding syntheses of related five-membered cyclic ethers. This synthetic pathway has the potential for a wide range of applications. Distinctive cyclic ethers and industrially relevant compounds were synthesized in quantitative yield. The reaction mechanism for the cyclization was investigated. Notably, the chirality of the starting material was maintained. DFT calculations indicated that the formation of five-membered cyclic ethers was energetically the most favorable pathway. Typically, the selectivity exhibited by these systems could be rationalized on the basis of hard-soft acid-base theory. Such principles were applicable as far as computed energy barriers were concerned, but in practice cyclization reactions were shown to be entropically driven. Copyright
- Aricó, Fabio,Tundo, Pietro,Maranzana, Andrea,Tonachini, Glauco
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experimental part
p. 1578 - 1586
(2012/10/07)
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- Trans-tetrahydrofurans by OH-assisted Ru-catalyzed isomerization of 2-butene-1,4-diols
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We herein report a general method for the synthesis of 1,2-annulated trans-tetrahydrofurans by the OH-assisted Ru-catalyzed isomerization of (Z)-2-butene-1,4-diols (using Chaudret's catalyst), followed by reduction of the incipient lactol (using Et3SiH and Amberlyst 15). Alternatively, the lactol can be oxidized to the corresponding lactone (using Ikariya's catalyst). It was shown by labeling experiments that an addition/elimination pathway is (at least to some extent) operative for the isomerization reaction. Only 0.5 mol-% of Chaudret's Ru catalyst is sufficient for the rapid and stereoselective isomerization of enediols of the type shown. This allows ready access to trans-tetrahydrofurans.
- Fehr, Charles,Magpantay, Iris,Saudan, Lionel,Sommer, Horst
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scheme or table
p. 6153 - 6156
(2010/12/29)
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- PROCESS FOR THE PREPARATION OF TETRANORLABDANE DERIVATIVES
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The present invention concerns a process for the preparation of a compound of formula (I), wherein the dotted line is a single bond and n is 1 or the dotted line is a double bond and n is 0, and wherein the relative configuration is as shown, in the form of any one of its diastereoisomers or enantiomers or mixtures thereof.
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Page/Page column 13
(2009/05/30)
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- PROCESS FOR THE PREPARATION OF TETRANORLABDANE DERIVATIVES
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The present invention concerns a process for the preparation of a compound of formula (I) wherein the dotted line is a single bond and n is 1 or the dotted line is a double bond and n is 0, and wherein the relative configuration is as shown, in the form of any one of its diastereoisomers or enantiomers or mixtures thereof.
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Page/Page column 12-13
(2009/05/30)
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- Internal nucleophilic termination in acid-mediated polyene cyclizations part 3. Synthetic access to didehydro and methyl didehydro analogues of (±)-ambrox
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Treatment of the unsaturated allenic alcohols (E)-7, (Z)-7, 10, 13, and 19 with an excess of FSO3H in 2-nitropropane at -90° to -30° afforded, in 68-85% yield, diastereoisomer mixtures of racemic tricyclic ethers 14a-d and 20a-d, respectively (Schemes 3 and 5), with high stereoselectivity (see Table and Scheme 6). These stereospecific transformations represent the first reported examples of an acid-mediated polyene cyclization, in which an alkene is the initiating group and an allenic alcohol serves as the internal terminator. In close analogy to our earlier work, a nonsynchronous process is postulated, whereby the stereochemical course of cyclization is directed by the conformational structure of an intermediate cyclohexyl cation (see Schemes 3 and 6). In addition, the organoleptic properties of 14c and 20c, racemic didehydro and methyl didehydro analogues, respectively, of the known odorant Ambrox ((-)-4f), are briefly discussed.
- Snowden, Roger L.,Eichenberger, Jean-Claude,Linder, Simon,Sonnay, Philippe
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p. 1711 - 1723
(2007/10/03)
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- Conversion of Esters and Lactones to Ethers via Thionoesters and Thionolactones Using Reductive Radical Desulfurization
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Various thionoesters and thionolactones are readily reduced into the corresponding ethers in high isolated yields by radical desulfuurization with organotin hydrides and Et3B under mild reaction conditions.
- Jang, Doo Ok,Song, Seong Ho,Cho, Dae Hyan
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p. 3479 - 3488
(2007/10/03)
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- Synthesis of d,l-Norlabdane Oxide and Related Odorants: An Intramolecular Radical Approach
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A cascade radical approach to d,l-norlabdane oxide and related odorants is reported. Oxidative radical cyclization of polyene 4 with Mn(III) and Cu(II) afforded exclusively bicycle 3, which upon acid treatment gave tricycle 2 possessing the norlabdane oxide skeleton with a modified A-ring system. Tricycle 2 was ultimately converted to d, l-norlabdane oxide 1 and to several new A-ring labdane oxides as potential odorants.
- Zoretic, Phillip A.,Fang, Haiquan,Ribeiro, Anthony A.
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p. 4779 - 4785
(2007/10/03)
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- STUDIES TOWARD THE TOTAL SYNTHESIS OF POLYOXYGENATED LABDANES: PRELIMINARY APPROACHES
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Using the keto-ester 3 as a starting material, methods are developed for the successive introduction of hydroxy groups at C-6, C-7 and C-8 of a decalin system, as well as for elaboration of a C-9 pentadiene chain in preliminary approach to the total synthesis of trihydroxylabdadienes.
- Herlem, Denyse,Kervagoret, Jocelyne,Dahai, Yu,Khuong-Huu, Francoise,Kende, Andrew S.
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p. 607 - 618
(2007/10/02)
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- Internal Nucleophilic Termination in Biomimetic Acid Mediated polyene Cyclizations: Stereochemical and Mechanistic Implications. Synthesis of (+/-)-Ambrox and Its Diastereoisomers
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Treatment of 10 structurally releted trienols and dienols 5-8 with an excess of fluorosulfonic acid in 2-nitropropane at -90 deg C afforded, in 74-87percent yield, diastereoisomeric mixtures of the odoriferous norlabdane oxides 9-15 ((-)-9 (Ambrox) is a naturally occuring ambergris odorant).These tranformations represent examples of efficientbiomimetic acid-mediated cyclizations in which the hydroxyl group serves as the internal nucleophilic terminator.The stereochemical outcome of these kinetically controlled processes has been analysed in detail, and mechanistic hypotheses consistent with the results have been proposed.For the four acyclic trienols 5, the major reaction pathway can be rationalized by a totally synchronous process involving three internal anti additions via chair or skew-boat conformations of the nascent cyclohexane rings.An alternative explanation postulates a nonsynchronous process in which ring closure to an intermediate cyclohexyl cation is followed by rapid cyclization, directed by a strong kinetic preference for equatorial C-C and C-O bond formation.In contrast, for the monocyclic dienols 6-8 only a nonsynchronous process, involving prior protonation of the cyclohexenyl bond, is fully consisitent with the results.In the nonsynchronous processes, the orientation of the side chain vicinal to the cyclohexyl cation directs the stereochemical course of the cyclization.For the acyclic trienols, this factor is predetermined by the configuration of the C(7)=C(8) bond, whereas, for the monocyclic dienols, this orientation is determined by the stereoselective axial protonation of the cyclohexenyl bond in 6, or by the distribution of cyclohexene and cyclohexane conformers in 7 and 8, respectively.In the cases studied, it is clear that conformational inversion of the six-membered ring is slower than cyclization and thus ensures that an equatorial side chain leads to a trans A/B ring junction in the cyclization product, whereas an axial side chain affords a cis A/B ring junction.
- Snowden, Roger L.,Eichenberger, Jean-Claude,Linder, Simon M.,Sonnay, Philippe,Vial, Christian,Schulte-Elte, Karl H.
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p. 955 - 960
(2007/10/02)
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- SYNTHESIS OF 3a,6,6,9a-TETRAMETHYL-trans-PERHYDRONAPHTOFURAN AND 4a,7,7,10a-TETRAMETHYL-trans-PERHYDRONAPHTHOPYRAN
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The compounds 3a,6,6,9a-tetramethyl-trans-perhydronaphthofuran (ambrox or ambroxide) and 4a,7,7,10a-tetramethyl-trans-perhydronaphthopyran (homofixator) - substances important in the perfume industry - have been synthesized by superacid cyclization of E,E-homofarnesol and E,E-bishomofarnesol or mixtures of the isomeric bicyclohomofarnesenses or bicyclobishomofarnesenols.Superacid cyclization of these alcohols was shown to be an effective structurally selective and stereospecific method of obtaining ambroxide and homofixator.
- Vlad, P. F.,Ungur, N. D.,Perutskii, V. B.
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p. 746 - 750
(2007/10/02)
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- Configuration-Odor Relationship in 5β-Ambrox
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The four possible A/B cis-fused diastereomers of Ambrox have been synthesized and their configurations and conformations established by X-ray and NMR analysis.Only 5β-ambrox (=1,2,3a,4,5,5aβ,6,7,8,9,9a,9bα-dodecahydro-3aβ,6,6,9aβ-tetramethylnaphthofuran; 5) has an odor quality comparable to Ambrox.The 1,3-synperiplanar/diaxial conformation of the substituents at C(8) (=C(3a)) and C(10) (=C(9a)) has thus been confirmed to be a compulsory structure element for the particular odor.
- Escher, Sina,Giersch, Wolfgang,Niclass, Yvan,Bernardinelli, Gerald,Ohloff, Guenther
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p. 1935 - 1947
(2007/10/02)
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- 110. The Synthesis of Racemic Ambrox
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(+/-)-Ambrox (10), the racemic form of (-)-Ambrox, the commercially most important ambergris odorant has been synthesized from a readily available bicyclic keto ester in five steps.The racemic ether retains the characteristic scent of fine-quality ambergris, and the odor threshold of the racemate and the (-)-enantiomer prepared from natural sclareol found to be essentially identical.
- Buechi, George,Wueest, Hans
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p. 996 - 1000
(2007/10/02)
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- New Syntheses of (+/-)-Ambrox, (+/-)-Ambra Oxide and Their Stereoisomers
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New and efficient syntheses of (+/-)-ambrox (1a), (+/-)-ambra oxide (2a) and their stereoisomers (1b, 2b ca. c), amber-like odorous compounds, are described.Starting from dihydro β- and α-ionone (5,12), these substances were obtained in only a few steps via stereoselective acid-catalized cyclization of monocyclodienoic acid (7a ca. b, 11a ca. b, 15a).
- Kawanobe,Tsuneo,Kogami, Kunio,Matsui, Masanao
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p. 1475 - 1480
(2007/10/02)
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