- Re-visiting the diastereoselectivity of organocatalytic conjugate addition of 2-trimethylsiloxyfuran to trans-crotonaldehyde
-
We describe the re-assignment of configuration previously ascribed to product diastereomers resultant from imidazolidinone-catalyzed conjugate addition of 2-trimethylsiloxyfuran to trans-crotonaldehyde. A modified procedure that uses a diphenylprolinol catalyst was subsequently developed to selectively provide the ‘syn’ diastereomeric product in high enantiomeric excess on decagram scales.
- Li, Liubo,El Khoury, Anton,Clement, Brennan O.,Harran, Patrick G.
-
supporting information
(2021/04/22)
-
- Facile and highly diastereoselective synthesis of 3-aminooxindoles via AgOAc-catalyzed vinylogous Mannich reaction
-
A novel AgOAc-catalyzed vinylogous Mannich reaction between easily prepared imines 1 derived from isatins and trimethylsilyloxyfuran 2 (TMSOF) was developed. This method provided a facile synthetic route to get access to synthetically useful quaternary 3-aminooxindole in excellent yields (94-99%) and diastereoselectivities (>99:1).
- Shi, Yu-Hua,Wang, Zheng,Shi, Ying,Deng, Wei-Ping
-
experimental part
p. 3649 - 3653
(2012/06/18)
-
- Stereoselective triplet-sensitised radical reactions of furanone derivatives
-
The stereo- and regioselectivity of triplet-sensitised radical reactions of furanone derivatives have been investigated. Furanones 7a,b were excited to the 3ππ* state by triplet energy transfer from acetone. Intramolecular hydrogen abstraction then occurred such that hydrogen was transferred from the tetrahydropyran to the β position of the furanone moiety. Radical combination of the tetrahydropyranyl and the oxoallyl radicals led to the final products 8a,b. In the intramolecular reaction, overall, a pyranyl group adds to the a position of the furanone. The effect of conformation was first investigated with compounds 9a,b carrying an additional substituent on the tether between the furanone and pyranyl moiety. Further information on the effect of conformation and the relative configuration at the pyranyl anomeric centre and the furanone moiety was obtained from the transformations of the glucose derivatives 12, 14, 17 and 18. Radical abstraction occurred at the anomeric centre and at the S′-position of the glucosyl moiety. Computational studies of the hydrogen-abstraction step were carried out with model structures. The activation barriers of this step for different stereoisomers and the abstraction at the anomeric centre and at the 6' -position of the tetrahydropyranyl moiety were calculated. The results of this investigation are in accordance with experimental observations. Furthermore, they reveal that the reactivity and regioselectivity are mainly determined in the hydrogen-abstraction step. Intramolecular hydrogen abstraction (almost simultaneous electron and proton transfer) in 3ππ * excited furanones only takes place under restricted structural conditions in a limited number of conformations that are defined by the relative configuration of the substrates. It is observed that in the biradical intermediate, back-hydrogen transfer occurs leading to the starting compound. In the case of glucose derivatives, this reaction led to epimerisation at the anomeric centre.
- Jahjah, Rabih,Gassama, Abdoulaye,Bulach, Veronique,Suzuki, Chikako,Abe, Manabu,Hoffmann, Norbert,Martinez, Agathe,Nuzillard, Jean-Marc
-
supporting information; experimental part
p. 3341 - 3354
(2010/06/19)
-
- Preparation of silica supported tin chloride: As a recyclable catalyst for the silylation of hydroxyl groups with HMDS
-
Silica-supported tin chloride [SiO2-Sn(Cl)4-n] has been prepared by mixing tin chloride with activated silica gel in toluene under refluxing conditions for one day. Arange of primary, secondary, and tertiary alcohols as well as phenolic hydroxyl groups were converted into their corresponding trimethylsilyl ethers with hexamethyldisilazane in the presence of catalytic amounts of silica-supported tin chloride at room temperature. An excellent chemoselective silylation of hydroxyl groups in the presence of other functional groups was also observed. This catalyst could be recycled and reused fifteen times without loss of efficiency.
- Niknam, Khodabakhsh,Zolfigol, Mohammad Ali,Saberi, Dariush,Molaee, Hajar
-
experimental part
p. 1257 - 1264
(2010/08/19)
-
- Total synthesis of (+)-azaspiracid-1. An exhibition of the intricacies of complex molecule synthesis
-
The synthesis of the marine neurotoxin azaspiracid-1 has been accomplished. The individual fragments were synthesized by catalytic enantioselective processes: A hetero-Diels-Alder reaction to afford the E- and HI-ring fragments, a carbonyl-ene reaction to furnish the CD-ring fragment, and a Mukaiyama aldol reaction to deliver the FG-ring fragment. The subsequent fragment couplings were accomplished by aldol and sulfone anion methodologies. All ketalization events to form the nonacyclic target were accomplished under equilibrating conditions utilizing the imbedded configurations of the molecule to adopt one favored conformation. A final fragment coupling of the anomeric EFGHI-sulfone anion to the ABCD-aldehyde completed the convergent synthesis of (+)-azaspiracid-1.
- Evans, David A.,Kvaerno, Lisbet,Dunn, Travis B.,Beauchemin, Andre,Raymer, Brian,Mulder, Jason A.,Olhava, Edward J.,Juhl, Martin,Kagechika, Katsuji,Favor, David A.
-
supporting information; experimental part
p. 16295 - 16309
(2009/05/08)
-
- 2,5-Dimethoxy-2,5-dihydrofuran chemistry: a new approach to 2(5H)-furanone derivatives
-
2,5-Dimethoxy-2,5-dihydrofuran is a synthetic equivalent of 2(5H)-furanone or 2-trimethylsilyloxyfuran, useful C4 synthons in the preparation of 5-substituted-2(5H)-furanone derivatives. The reaction conditions adopted allow to obtain different classes of complex and biologically interesting compounds, in only one step, with high yields.
- Garzelli,Samaritani,Malanga
-
p. 4183 - 4186
(2008/09/20)
-
- Toward the development of a general chiral auxiliary. Enantioselective alkylation and a new catalytic asymmetric addition of silyloxyfurans: Application to a total synthesis of (-)-rasfonin
-
An enantioselective total synthesis of the apoptosis-inducing natural product, (-)-rasfonin, is described. Camphor lactam-mediated asymmetric alkylation reactions enabled the installation of three stereogenic centers with >95:5 diastereoselectivity. A modified Corey-Peterson olefination was employed in the construction of the (E,E)-diene system. A highly diastereoselective, asymmetric vinylogous Mukaiyama aldol addition was conducted using a chiral cationic oxazaborolidine catalyst. The pyranone core of the natural product was prepared via a DBU-promoted rearrangement of a furanol to its corresponding pyranol with concomitant [1,4]-silyl transfer. Copyright
- Boeckman Jr., Robert K.,Pero, Joseph E.,Boehmler, Debra J.
-
p. 11032 - 11033
(2007/10/03)
-
- Synthesis of furanone-based natural product analogues with quorum sensing antagonist activity
-
The synthesis of 5- and 3-(1′-hydroxyalkyl)-substituted 5H-furan-2-ones 4a-d and 8a-d as well as 5-alkylidene-5H-furan-2-ones 5a-d is described. A study of the structure-activity relationship of these furanone-based natural product analogues towards two different quorum sensing systems is reported. Although the synthesized compounds are not as potent quorum sensing inhibitors as some natural counterparts and a synthetic analogue hereof, interesting structure-activity relationships are seen.
- Hjelmgaard, Thomas,Persson, Tobias,Rasmussen, Thomas B.,Givskov, Michael,Nielsen, John
-
p. 3261 - 3271
(2007/10/03)
-
- Stereoselective synthesis of freelingyne and related γ-alkylidenebutenolides via vinylogous Mukaiyama aldol additions
-
Following the strategy of Scheme 1, a Mukaiyama aldol addition/anti-elimination route to stereopure γ-alkylidenebutenolides 4 was established. The addition giving 27 was only moderately diastereoselective but the products lk- and ul-27 were chromatographically separable (Scheme 4). They underwent highly selective anti-eliminations in the presence of triflic anhydride-pyridine or Burgess' reagent, furnishing the thiophene-containing butenolides Z- and E-28, respectively (Scheme 5). The Mukaiyama aldol addition leading to compound 29 was 100% lk-selective when mediated by BF3 etherate and 87 : 13 ul-selective in the presence of ZnBr2 (Scheme 6). Stephens-Castro couplings of the resulting butenolides lk- and ul-29 with 3-ethynylfuran proceeded with complete conservation of the stereochemical integrity (Scheme 7). The subsequent anti-eliminations of water were best realized by treatment with DEAD-PPh3. They provided freelingyne (Z-9) with ds = 92 : 8 and its isomer E-9 with ds = 98 : 2 (Scheme 8). Analogously, the differently substituted (trimethylsiloxy)furans 15 or 16 provided the freelingyne analogs Z-10, E-10 and Z-11 (Schemes 6-8).
- Von der Ohe,Bruckner
-
p. 659 - 669
(2007/10/03)
-
- Asymmetric synthesis of butenolide and butyrolactone derivatives
-
2-Trimethylsiloxyfuran and 4-methoxy-2-trimethylsiloxyfuran, which are readily prepared from butenolide and methyl tetronate respectively, have been reacted with a series of homochiral ortho-esters and oxazolidine derivatives in the presence of Lewis acids to afford homochiral 2(5H)-furanone derivatives. The structures of three products have been determined using nmr spectroscopy and, where possible, by X-ray analysis. Preliminary experiments have been carried out involving conjugate addition to these unsaturated lactones, demonstrating their potential as substrates for natural product synthesis.
- Pelter,Ward,Sirit
-
p. 1745 - 1762
(2007/10/02)
-
- Synthesis of the cis-3a,8b-Dihydrofurobenzofuran-2(3H)-one Ring System via a Furofuran Annulation to Activated Benzoquinones
-
The uncatalysed addition of 2-(trimethylsiloxy)furan (4) to the 1,4-benzoquinones (5a-e) containing electron-withdrawing groups at C-2 gave the cis-3a,8b-dihydrofurobenzofuran-2(3H)-ones (6a-e) in 51-76percent yields.The 1,4-benzoquinones (5f, g, h) without electron-withdrawing groups at C-2 failed to undergo the furofuran annulation, with none of the desired adducts (6f, g, h) being isolated.The carboxylic acid adduct (6i; R=CO2H) was prepared indirectly by reductive hydrolysis of either the phenacyl adduct (6e) or the trichloroethyl ester adduct (6d) using zinc in acetic acid (9).Treatment of the methyl ketone adduct (6b) with acid effected a ring opening to the corresponding (benzofuran-2-yl)acetic acid.
- Brimble, Margaret A.,Brimble, Mark T.,Gibson, Jennifer J.
-
p. 179 - 184
(2007/10/02)
-
- Tautomerism of the Monohydroxy Derivatives of Five-Membered O, N, and S Heterocycles
-
The O-deuterated enolic tautomers 3-deuteroxybenzofuran, 3-deuteroxybenzothiophene, 3-deuteroxyindole, 3-deuteroxy-1-methylindole, 3-deuteroxyfuran, 3-deuteroxythiophene, 2-deuteroxybenzothiophene, and 2-deuteroxythiophene have been generated in solution in mixtures of CD3COCD3, CD3CN, or CD3SOCD3 with D2O by hydrolysis of their trimethylsilyl derivatives in the presence of DCl (1E-3 - 1E-4 M) and characterized by 1H NMR spectroscopy.Solutions of 3-hydroxypyrrole and of 3-hydroxy-1-methylpyrrole were obtained by methanolysis of their trimethylsilyl derivatives,evaporation of the methanol, and immediate dissolution in DMSO-d6.The carbocyclic analogues of the bicyclic heterocyclic enols 3-deuteroxyindene and 2-deuteroxyindene were also generated in solution.Attempts to prepare solutions of 2-deuteroxyfuran, 2-deuteroxypyrrole, and 2-deuteroxy-1-methylpyrrole were unsuccessful.The kinetics of ketonization of the OH forms of these enols have been investigated in water or aqueous acetonitrile solution.The equilibrium constants for the keto-enol tautomerism were also determined either by direct measurement when sufficient enol was present at equilibrium or as the ratio of the rate constant for enolization of the keto form to that for ketonization of the enol form, the former being determined by the iodine-trapping technique.The effect of solvent on the equilibrium constants was also studied.Sufficient data were available for the equilibrium between 3-hydroxyindole and 3-ketoindole for them to be analyzed by the four-parameter equation of Mills and Beak to yield an a value of 2.4 and a b value of -3.0.The pKas of the bicyclic enols were measured. 3-Hydroxybenzofuran and3-hydroxybenzothiophene are stronger acids than 3-hydroxyindole and 3-hydroxy-1-methylindole.The ketonization reactions are general acid and general base catalyzed and their mechanisms are discussed.
- Capon, Brian,Kwok, Fu-Chiu
-
p. 5346 - 5356
(2007/10/02)
-
- Synthesis of Trimethylsilyloxy and Hydroxy Compounds from Carbanions and Bis(trimethylsilyl)peroxide.
-
The reactions of bis(trimethylsilyl)peroxide with alkyl, vinyl, alkynyl, aromatic and heteroaromatic anions are described.Depending on the reaction conditions, the trimethylsilyloxy derivatives can be obtained alone or together with the corresponding trimethylsilyl derivatives, which is sometimes the major product.Enolates, generated using magnesium diisopropylamide give the corresponding hydroxycarbonyl compounds in good yields.An attempt to rationalise the above results is given, emphasising the wide use of bis(trimethylsilyl)peroxide in organic synthesis as an electrophilic hydroxylation reagent.
- Camici, Lucia,Dembech, Pasquale,Ricci, Alfredo,Seconi, Giancarlo,Taddei, Maurizio
-
p. 4197 - 4206
(2007/10/02)
-
- REGIOSELECTIVE FUNCTIONALIZATION OF THE Δαβ-BUTENOLIDE RING VIA GROUP IV-B ORGANOMETALLICS
-
The Δα,β-butenolide ring reacts with amino- and thiosilanes to give 4-substituted γ-butyrolactone and siloxyfuran.The latter undergoes regiospecific functionalization at the 5 position with benzaldehyde under F- catalysis.
- Fiorenza, Mariella,Ricci, Alfredo,Romanelli, M. Novella,Taddei, Maurizio,Dembech, Pasquale,Seconi, Giancarlo
-
p. 2327 - 2329
(2007/10/02)
-