- Stereoselective Total Synthesis of Atractylodemayne A, a Conjugated 2(E),8(Z),10(E)-Triene-4,6-diyne
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The first total synthesis of the polyacetylene natural product atractylodemayne A is reported. Stereoselective construction of the conjugated 8(Z),10(E)-diene moiety was achieved through a tethered ring-closing metathesis approach, comprising a Ru-catalyz
- Schmidt, Bernd,Aud?rsch, Stephan
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- Electron Impact Induced Fragmentation of β-Allenic and γ-Acetylenic Alcohols
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The main fragmentation pathway of ionized hydroxyallenes (1) consists of a methyl loss.Extensive deuterium-labelling experiments indicate that the terminal allenic carbon is implied in this fragmentation.Collisional activation spectra indicate a propenyl-acylium structure (a) for these (+) ions which can originate from a 1,4-hydroxyl migration followed by hydrogen rearrangements.Isomeric hydroxyacetylenes (2) behave similarly, also giving rise, by methyl loss, to acylium ions a.It is proposed that 2(+) radical is irreversibly isomerized into 1(+) radical by a 1,3-hydrogen transfer 'catalysed' by the hydroxy group.The proposed internal proton-bound complex justifies also the easier loss of water from 2(+) radical.Ethyl loss is also a prominent fragmentation for the hydroxyallene and hydroxyacetylene homologues.
- Arseniyadis, Simeon,Maquestiau, Andre,Flammang, Robert,Guenot, Pierre,Carrie, Robert
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- Stereoselective synthesis of the side chains of mycolactones A and B featuring stepwise double substitutions of 1,1-dibromo-1-alkenes
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(Chemical Equation Presented) Piecing them together: The side chains of mycolactones A and B are synthesized with a high degree of stereoselectivity. The components of the side chains are prepared separately, then combined through Pd-catalyzed cross-coupling (see scheme; Z1 = tert- butyldimethylsilyl, Z2 = methoxymethyl, TBAF = tetra-n-butylammonium fluoride).
- Yin, Ning,Wang, Guangwei,Qian, Mingxing,Negishi, Eiichi
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- Possibility of [1,5] sigmatropic shifts in bicyclo[4.2.0]octa-2,4-dienes
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The thermal equilibration of the methyl esters of endiandric acids D and E was subject to a computational study. An electrocyclic pathway via an electrocyclic ring opening followed by a ring flip and a subsequent electrocyclization proposed by Nicolaou [ Nicolaou, K. C.; Chen, J. S. Chem. Soc. Rev. 2009, 38, 2993 ], was computationally explored. The free-energy barrier for this electrocyclic route was shown to be very close to the bicyclo[4.2.0]octa-2,4-diene reported by Huisgen [ Huisgen, R.; Boche, G.; Dahmen, A.; Hechtl, W. Tetrahedron Lett. 1968, 5215 ]. Furthermore, the possibility of a [1,5] sigmatropic alkyl group shift of bicyclo[4.2.0]octa-2,4-diene systems at high temperatures was explored in a combined computational and experimental study. Calculated reaction barriers for an open-shell singlet biradical-mediated stepwise [1,5] sigmatropic alkyl group shift were shown to be comparable with the reaction barriers for the bicyclo[4.1.0]hepta-2,4-diene (norcaradiene) walk rearrangement. However, the stepwise sigmatropic pathway is suggested to only be feasible for appropriately substituted compounds. Experiments conducted on a deuterated analogous diol derivative confirmed the calculated (large) differences in barriers between electrocyclic and sigmatropic pathways.
- Goossens, Hannelore,Winne, Johan M.,Wouters, Sebastian,Hermosilla, Laura,De Clercq, Pierre J.,Waroquier, Michel,Van Speybroeck, Veronique,Catak, Saron
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- Search for highly efficient, stereoselective, and practical synthesis of complex organic compounds of medicinal importance as exemplified by the synthesis of the C21-C37 fragment of amphotericinb
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Highly stereoselective: A highly efficient, stereoselective and practical synthesis of the C21-C37 fragment of amphotericinB was realized in 25 % overall yield in eight longest linear steps from commercially available ethyl (S)-3-hydroxybutyrate by using Fráter-Seebach alkylation, Brown crotylboration, Negishi coupling, Heck reaction, and Horner-Wadsworth-Emmons (HWE) olefination as key steps (see diagram). Copyright
- Wang, Guangwei,Xu, Shiqing,Hu, Qian,Zeng, Fanxing,Negishi, Ei-Ichi
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- Highly stereoselective total synthesis of fully hydroxy-protected mycolactones A and B and their stereoisomerization upon deprotection
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Unprecedentedly efficient and highly (≥98 %) stereoselective syntheses of mycolactones A and B side chains relied heavily on Pd-catalyzed alkenylation (Negishi version) and were completed in 11 longest linear steps from ethyl (S)-3-hydroxybutyrate in 12 % and 11 % overall yield, respectively, roughly corresponding to an average of 82 % yield per step. The synthesis of mycolactone core was realized by using Pd-catalyzed alkenyl-allyl coupling and an epoxide-opening reaction with a trialkylalkenylaluminate as key steps. Fully hydroxy-protected mycolactones A and B of ≥98 % isomeric purity were synthesized successfully for the first time. However, unexpected 4:3-5:4 inseparable mixtures of mycolactones A and B were obtained upon deprotection. Copyright
- Wang, Guangwei,Yin, Ning,Negishi, Ei-Ichi
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- On the Mechanism of Propynyloxirane Rearrangement
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Abstract: The most probable mechanism for the opening of the oxirane ring in propynyloxirane (3-ethynyl-1,2-epoxypropane) is presented. Due to the rearrangement, a mixture of the Z and E isomers of enyne alcohols is formed. The 1H NMR data and quantum-chemical calculations revealed intramolecular interactions between the π-electrons of the triple bond and the OH proton in the six-membered ring of the Z isomer.
- Abdullaev, T. Kh.,Fayzilov, I. U.,Isobaev, M. D.,Jumaeva, M. I.
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p. 1853 - 1860
(2021/12/22)
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- Polyunsaturated C-Glycosidic 4-Hydroxy-2-pyrone Derivatives: Total Synthesis Shows that Putative Orevactaene Is Likely Identical with Epipyrone A
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Orevactaene and epipyrone A were previously thought to comprise the same polyunsaturated tail but notably different C-glycosylated 4-hydroxy-2-pyrone head groups. Total synthesis now shows that the signature bicyclic framework assigned to orevactaene is a chimera; the compound is almost certainly identical with epipyrone A, whose previously unknown stereochemistry has also been established during this study. Key to success was the ready formation of the bicyclic core of putative orevactaene by a sequence of two alkyne cycloisomerization reactions using tungsten and gold catalysis. Equally important was the flexibility in the assembly process gained by the use of heterobimetallic polyunsaturated modules whose termini could be selectively and consecutively addressed in a practical one-pot cross-coupling sequence.
- Preindl, Johannes,Schulthoff, Saskia,Wirtz, Conny,Lingnau, Julia,Fürstner, Alois
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p. 7525 - 7530
(2017/06/13)
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- Chemo-, regio-, and stereoselective hydroboration of conjugated enyne alcohol/amine: Facile synthesis of Z,Z-/Z,E-1,3-dien-1/2-ylboronic ester bearing hydroxyl/amino group
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Hydroboration of conjugated enyne alcohol/amine is studied by using copper salts and bis(pinacolato)diboron as pre-catalysts and boron source respectively. It is suggested that the chemo-selectivity is derived from a combined electronic influence of the heteroatoms on the substrate and the ligand on the transition metal. The regioselectivity is probably dominated mainly by electronic effect of the alkyne substituent. This study resulted in a highly selective protocol to access Z,Z-/Z,E-1,3-dien-1/2-ylboronic ester bearing hydroxyl/amino group.
- Xu, Hua-Dong,Wu, Hao,Jiang, Chun,Chen, Peng,Shen, Mei-Hua
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supporting information
p. 2915 - 2918
(2016/06/14)
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- Synthesis of isomeric polyacetylenes based on natural hydroxy matricaria esters
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The construction of a library of natural and related polyacetylenes using a convergent synthetic strategy based on a palladium mediated cross-coupling reaction is described. The systematic synthetic study led to all possible alkene isomers of the hydroxy matricaria esters 29-32, and the corresponding tiglates 1-4. The synthesis of many of these compounds is described for the first time.
- Garrais, Solange,Turkington, Jennifer,Goldring, William P.D.
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experimental part
p. 8418 - 8427
(2009/12/26)
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- Efficient and selective syntheses of (all-E)- and (6E,10Z)-2′-O- methylmyxalamides D via Pd-catalyzed alkenylation-carbonyl olefination synergy
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(Chemical Equation Presented) Highly efficient and selective syntheses of both (all-E) and (6E,10Z)-isomers of 2′-O-methylmyxalamide D (2 and 3), in which the crucial conjugated pentaene moieties were assembled in ≥98% stereoselectivity through the use of
- Wang, Guangwei,Huang, Zhihong,Negishi, Ei-Ichi
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scheme or table
p. 3223 - 3226
(2009/05/27)
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- Total synthesis of 1-(Z)-atractylodinol
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The total synthesis of 1-(Z)-atractylodinol, a natural polyacetylenic alcohol with several biological activities, has been achieved using a newly developed telluride synthon and a novel use for the Negishi type coupling reaction employing vinyl tellurides.
- Oliveira, Juliana M.,Zeni, Gilson,Malvestiti, Ivani,Menezes, Paulo H.
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p. 8183 - 8185
(2007/10/03)
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- STEREOCONTROLLED SYNTHESIS OF NATURALLY-OCCURRING POLYACETYLENES CHARACTERIZED BY (E)-1-EN-3-YNE, (E)-1-EN-3,5-DIYNE, (1E,5E)-1,5-DIEN-3-YNE, AND (1E,7E)-1,7-DIEN-3,5-DIYNE MOIETIES
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A stereocontrolled synthesis of five naturally-occurring polyacetylenes, i.e. methyl (E)-5-(2-thienyl)-2-penten-4-ynoate, 9, (E)-N-methyl-N-(2-methylpropyl)-2-decen-4,6-diynamide, 10, (E)-1-(3-methyl-2-butenoyloxy)-2-decen-4,6-diyne, 11, (2E,6E)-1-acetoxy-2,6-decadien-4-yne, 12, and (2E,8E)-1-acetoxy-2,8-decadien-4,6-diyne, 13, is reported.The flexible strategy involves palladium(0)-copper(I) catalyzed coupling reactions to construct the carbon skeleton of the target molecules and to prepare an important C5 building block, i.e. (E)-2-penten-4-yn-1-ol, 21.This compound is also an useful intermediate to lipoxins A and B.A highly diastereoselective palladium-catalyzed carbon-carbon bond forming reaction, recently developed in our laboratory, has been used in a key synthetic step to compound 12.
- Carpita, Adriano,Neri, Dario,Rossi, Renzo
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p. 481 - 490
(2007/10/02)
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- Enantioselective Synthesis of D-erythro-Sphingosine and of Ceramide
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The enynol 2 was transformed into D-erythro-sphingosine 11 (7 steps, 46 percent) and into ceramide 1 (8 step, 41 percent overall yield).The key steps were the mono-epoxidation of the enynol 5 (Ti(t-BuO)4, (-)-D-diethyl tartrate, t-BuOOH) to 6 (86percent, >/= 98percent ee), the regioselective intramolecular opening of the oxirane 6 via the benzylurethane 7, and the reductive transformation of the acetylene 9 into the oxazolidinone 10 (Li, EtNH2, 88 percent).
- Julina, Radomir,Herzig, Thomas,Bernet, Bruno,Vasella, Andrea
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p. 368 - 373
(2007/10/02)
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- A STEREOSELECTIVE SYNTHESIS OF CORIOLIC ACID AND DIMORPHECOLIC ACID
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Described herein is a convenient synthesis of coriolic acid (1) and dimorphecolic acid (2), the two natural ionophores derived respectively from bovine heart mitochondria and also shown to be self defensive substances in rice plant against rice blast disease.
- Rao, A. V. Rama,Reddy, E. Rajarathnam,Sharma, G. V. M.,Yadagiri, P.,Yadav, J. S.
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p. 465 - 468
(2007/10/02)
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- Regioselective and Stereoselective Methods for the Synthesis of the Pentitols
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Several different approaches to the stereoselective synthesis of xylitol (1), as well as the other two pentitols, ribitol (2) and DL-arabinitol DL-(3), from the (Z)- and (E)-1-hydroxypentadienes (4) and (5) and the (Z)- and (E)-4,5-epoxypent-2-enals (6) and (7) are described.They rely upon either (a) epoxidations of allylic C=C double bonds followed by stereospecific (anti) and sometimes regioselective epoxide cleavages, or (b) syn-hydroxylations of allylic C=C double bonds.Employing approach (a), the (Z)-isomers (4) and (6) do not afford any ribitol (2) among the products and the (E)-isomers do not afford any xylitol (1).The consequences are reversed when approach (b) is adopted.The most convenient synthesis of xylitol (1) starts from the (Z)-isomer (6) of 4,5-epoxypent-2-enal.The formyl group in (6) is reduced, provided acidic work-up conditions are employed, to yield (Z)-(4RS)-4,5-epoxy-1-hydroxypent-2-ene (9), which is characterised as its acetate (10).Opening of the epoxide ring in (10) with acetate ion gives the triacetate (11), which is deacetylated to afford a key intermediate, (Z)-(4RS)-1,4,5-trihydroxypent-2-ene (12).Epoxidation of (12) with peracids (e.g. p-nitroperbenzoic acid) yields (t-butyl hydroperoxide with catalytically active Ti4+, V5+, and Mo6+ complexes fails) two epoxides (13) and (14), arbitrarily named isomers A (13) and B (14) subsequently shown to have the relative stereochemistries (2S,3R,4R) and (2R,3R,4R), respectively.Epoxide ring opening with acetate ion in acetic anhydride of the more abundant isomer B (14), obtained with 70percent diastereoselectivity, yields xylitol penta-acetate (16) as the major product (>80percent diastereoselectivity) along with small and trace amounts of the other two pentitol penta-acetates.Epoxide ring opening of isomer A with acetate ion in acetic anhydride is not a straightforward reaction for the most part and has been found to involve the intermediacy of an isolatable bicyclic orthoester (23) en route to some of the xylitol penta-acetate (16) formed as the principal stable product during this reaction.These variations of approach (a) constitute stereoselective syntheses of xylitol (1), which are claimed to be acceptable on a laboratory scale.They provide a slightly better route than an alternative one involving the transformations (4) -> (33) -> (34) -> (39) -> (16) -> (1), starting from (Z)-1-hydroxypenta-2,4-diene (4), principally because this particular precursor is less readily accessible than (Z)-4,5-epoxypent-2-enal (6).By contrast, the (E)-isomer (5) of 1-hydroxypenta-2,5-diene is obtainable in high yield from the reduction of vinyl acrylic acid and the analogous transformations (26) -> (27) -> (28) -> DL-(5) -> DL-(3)> provide a highly stereoselective (91percent) synthetic route to DL-arabinitol DL-(3).Osmium-catalysed syn-hydroxylation of (E)-(4RS)-triacetoxypent-2-ene (22), prepared from (E)-4,5-epoxypent-2-enal (7) in two steps (20) -> (22)>, provides yet another...
- Holland, David,Stoddart, J. Fraser
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p. 1553 - 1571
(2007/10/02)
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