13720-12-2Relevant articles and documents
Asymmetric Cation-Olefin Monocyclization by Engineered Squalene–Hopene Cyclases
Aeberli, Natalie,Berweger, Raphael,Bornscheuer, Uwe T.,Buller, Rebecca,Dossenbach, Sandro,Eichenberger, Michael,Eichhorn, Eric,Flachsmann, Felix,Hüppi, Sean,Hortencio, Lucas,Patsch, David,Voirol, Francis,Vollenweider, Sabine
, p. 26080 - 26086 (2021/09/20)
Squalene–hopene cyclases (SHCs) have great potential for the industrial synthesis of enantiopure cyclic terpenoids. A limitation of SHC catalysis has been the enzymes’ strict (S)-enantioselectivity at the stereocenter formed after the first cyclization step. To gain enantio-complementary access to valuable monocyclic terpenoids, an SHC-wild-type library including 18 novel homologs was set up. A previously not described SHC (AciSHC) was found to synthesize small amounts of monocyclic (R)-γ-dihydroionone from (E/Z)-geranylacetone. Using enzyme and process optimization, the conversion to the desired product was increased to 79 %. Notably, analyzed AciSHC variants could finely differentiate between the geometric geranylacetone isomers: While the (Z)-isomer yielded the desired monocyclic (R)-γ-dihydroionone (>99 % ee), the (E)-isomer was converted to the (S,S)-bicyclic ether (>95 % ee). Applying the knowledge gained from the observed stereodivergent and enantioselective transformations to an additional SHC-substrate pair, access to the complementary (S)-γ-dihydroionone (>99.9 % ee) could be obtained.
Gold- or Silver-Catalyzed Syntheses of Pyrones and Pyridine Derivatives: Mechanistic and Synthetic Aspects
Preindl, Johannes,Jouvin, Kvin,Laurich, Daniel,Seidel, Günter,Fürstner, Alois
supporting information, p. 237 - 247 (2016/01/25)
3-Oxo-5-alkynoic acid esters, on treatment with a carbophilic catalyst, undergo 6-endo-dig cyclization reactions to furnish either 2-pyrones or 4-pyrones in high yields. The regiochemical course can be dialed in by the proper choice of the alcohol part of the ester and the π-acid. This transformation is compatible with a variety of acid-sensitive groups as witnessed by a number of exigent applications to the total synthesis of natural products, including pseudopyronine A, hispidine, phellinin A, the radininol family, neurymenolide, violapyrone, wailupemycin and an unnamed brominated 4-pyrone of marine origin. Although the reaction proceeds well in neutral medium, the rate is largely increased when HOAc is used as solvent or co-solvent, which is thought to favor the protodeauration of the reactive alkenyl-gold intermediates as the likely rate-determining step of the catalytic cycle. Such intermediates are prone to undergo diauration as an off-cycle event that sequesters the catalyst; this notion is consistent with literature data and supported by the isolation of the gem-diaurated complexes 12 and 15. Furthermore, silver catalysis allowed access to be gained to 2-alkoxypyridine and 2-alkoxyisoquinoline derivatives starting from readily available imidate precursors.
Raney nickel: An efficient reagent to achieve the chemoselective hydrogenation of α,β-unsaturated carbonyl compounds
Barrero, Alejandro F.,Alvarez-Manzaneda,Chahboun, Rachid,Meneses
, p. 1663 - 1666 (2007/10/03)
Raney Nickel is an effective reagent to achieve the chemoselective reduction of conjugated olefins in σ,β-unsaturated carbonyl compounds that also contain isolated double bonds. Its use is also compatible with a variety of other functional groups.
Studies on the synthesis of acanthodoral and nanaimoal: Evaluation of cationic cyclization routes
Engler,Ali,Takusagawa
, p. 8456 - 8463 (2007/10/03)
Intramolecular Lewis acid-promoted reactions of α,β-unsaturated ketone 6 and aldehydes 7 and 8 were examined as potential routes to acanthodoral (1), a structurally interesting natural product. Ketone 6 afforded ene product 22 exclusively, and both 7 and 8 gave mixtures of bicyclic aldehydes 3 and 26 and tricyclic aldehyde 25. The latter most likely results from 7 by intramolecular cyclization of the alkene onto the Lewis acid-activated carbonyl moiety affording carbocation 31 followed by a 1,2-hydride shift and ring closure. Starting from 8, tricyclic aldehyde 25 apparently forms by cyclization to cation 35 and ring closure to cyclobutane 36, followed by ring opening to 31, the same cation as formed in reactions of 7. Nanaimoal (3) results from loss of H+ from 31, and bicyclic aldehyde 26 may be formed in a similar manner or by a concerted ene reaction. The configuration of 25 establishes that the stereochemistry of the initial cyclization to 31 precludes the possible use of this strategy for the synthesis of acanthodoral. However, acid-promoted cyclization of allylic alcohol 23 efficiently gives diene 29 which undergoes selective hydroboration/oxidation to afford nanaimoal.
Internal Nucleophilic Termination in Biomimetic Acid Mediated polyene Cyclizations: Stereochemical and Mechanistic Implications. Synthesis of (+/-)-Ambrox and Its Diastereoisomers
Snowden, Roger L.,Eichenberger, Jean-Claude,Linder, Simon M.,Sonnay, Philippe,Vial, Christian,Schulte-Elte, Karl H.
, p. 955 - 960 (2007/10/02)
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.
Total Synthesis of Dehydroambliol-A and Its Unnatural Z Isomer
Magatti, Charles V.,Kaminski, James J.,Rothberg, Irvin
, p. 3102 - 3108 (2007/10/02)
Convergent total syntheses of dehydroambliol-A (1a), its unnatural Z isomer 1b, and ambliofuran (2) are described.The syntheses utilized 2-(3'-furyl)-1,3-dithiane (6) as a common intermediate.Analysis of their proton and carbon magnetic resonance spectra confirm that in the natural product dehydroambliol-A and in synthetic dehydroambliol-A the Δ7-bond possesses the E geometry, while in the unnatural isomer of dehydroambliol-A, the Δ7-bond is of the Z configuration.
New Synthesis of γ-Homocyclogeranial, γ-Dihydroionone and Their Derivatives
Kawanobe, Tsuneo,Kogami, Kunio,Hayashi, Kazuo,Matsui, Masanao
, p. 461 - 464 (2007/10/02)
A new and efficient synthesis of γ-homocyclogeranial (4), γ-dihydroionone (3) and their derivatives, 5, 6, 7 and 8, volatile components of ambergris, is described.Their compounds were synthesized via Claisen rearrangement of (3,3-dimethylcyclohexenyl)methyl vinyl ether (14).
Sesquiterpenoid Constituents of the Liverwort, Ptychanthus striatus (LEHM. et LINDENB.) NEES
Takeda, Reiji,Naoki, Hideo,Iwashita, Takashi,Mizukawa, Kosei,Hirose, Yoshio,et al.
, p. 1125 - 1132 (2007/10/02)
Four sesquiterpenoids, striatene, striatol, β-monocyclonerolidol and ptychanolide, were isolated from the liverwort Ptychanthus striatus (LEHM. et LINDENB.)NEES. Their structures have been established by spectroscopic analysis and chemical transformation. Three of them, striatene, striatol and β-monocyclonerolidol, are interesting in terms of the evolution of the liverwort fom the algae.
STRUCTURAL AND ABSOLUTE CONFIGURATIONAL STUDIES OF STRIATENE, STRIATOL AND β-MONOCYCLONEROLIDOL, THREE SESQUITERPENOIDS FROM THE LIVERWORT PTYCHANTHUS STRIATUS (LEHM. ET LINDBEMB.) NEES
Takeda, Reiji,Mori, Reiko,Hirose, Yoshio
, p. 1625 - 1628 (2007/10/02)
Three new sesquiterpenoids, striatene, striatol and β-monocyclonerolidol, were isolated from the liverwort Ptychanthus striatus (Lehm. et Lindemb.) Nees.Their structures have been established by spectroscopic analysis and chemical transformation.These compounds are interesting in terms of the evolution of the liverwort from algae.
Synthesis of trans-γ-Monocyclofarnesol
Vig, O. P.,Sharma, M. L.,Trehan, Navneet,Verma, N. K.
, p. 450 - 452 (2007/10/02)
The starting material, 2-formyl-6,6,dimethylcyclohexanone (II) in the synthesis of the title compound, is converted into the corresponding 2-isobutoxymethylene-6,6-dimethylcylohexanone (III).Reduction of (III) with LAH followed by treatment with 50percent sulphuric acid gives the α,β-unsaturated aldehyde (IV).LAH reduction of IV yields 1-hydroxymethyl-3,3-dimethylcylohex-1-ene (V) which on mercuric acetate catalysed transetherification with ethyl vinyl ether affords the vinyl ether (VI).Claisen rearragement of VI under an inert atmosphere furnishes 2-(6',6'-dimethyl-2'-methylenecylohexyl)ethanal (VII).Aldehyd VII on Wittig reaction with methoxymethylenetriphenylphosphorane provides the ether (VIII) which is readily converted into the ketal (IX) on treatment with ethylene glycol in the presence of catalytic amount of PTS in dry benzene.Deketalisation of IX with PTS in aq. acetone gives the aldehyde (X) which on Grignard reaction with methylmagnesium iodide furnishes 4-(6',6'-dimethyl-2'-methylenecylohexyl)butan-2-ol (XI).Oxidation of XI with pyridinium chlorochromate in anhydrous methylene chloride yields the ketone (XII) which when subjected to Grignard reaction with vinylmagnesium bromide in dry THF provides the vinylic alcohol (XIII).Treatment of XIII with acetic anhydride and glacical acetic acid in the presence of PTS furnishes the allylic acetate (XIV) which on refluxing with methanolic potassium hydroxide in the presence of a little water gives trans-γ-monocyclofarnesol (I).
