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Search for "Wittig" in Full Text gives 217 result(s) in Beilstein Journal of Organic Chemistry. Showing first 200.
Reactions of nitroxides 15. Cinnamates bearing a nitroxyl moiety synthesized using a Mizoroki–Heck cross-coupling reaction
Beilstein J. Org. Chem. 2015, 11, 1155–1162, doi:10.3762/bjoc.11.130
- Toxicology (in the 70s). The most recent reviews in this series were published in 2011 [10][11]. Cinnamic acid derivatives can be synthesized using Perkin, Knoevenagel, Claisen [7], and Wittig [12] condensation reactions. Since the discovery of catalytic coupling reactions, cinnamic derivatives have also
Direct access to pyrido/pyrrolo[2,1-b]quinazolin-9(1H)-ones through silver-mediated intramolecular alkyne hydroamination reactions
Beilstein J. Org. Chem. 2015, 11, 416–424, doi:10.3762/bjoc.11.47
- -insertion reaction [7], the cycloaddition of anthranilic acid iminoketene to a methyl butyrolactam through a sulfinamide anhydride intermediate [9], the intramolecular aza-Wittig reaction with an azide substrate [10], and the cycloaddition of anthranilamide [11]. For the synthesis of vasicinone (5
Attempts to prepare an all-carbon indigoid system
Beilstein J. Org. Chem. 2015, 11, 363–372, doi:10.3762/bjoc.11.42
- , and then oxidizing the presumably resulting carbanion to 21 (a known compound [19]) with Cu(OTf)2, which gave cleaner results than the chloride employed previously. Unfortunately, all efforts to convert 21 into 4 failed. Thus neither the Wittig reaction of 21 (MeP(Ph)3Br/n-BuLi, THF) nor its treatment
- that caused all these preparative difficulties, we next decided to investigate the behavior of diketone 19, in which this conjugation is interrupted. Although its methylenation under Wittig conditions was again unsuccessful, the reaction with the Tebbe’s reagent provided a product. This, however, was
Electrochemical selenium- and iodonium-initiated cyclisation of hydroxy-functionalised 1,4-dienes
Beilstein J. Org. Chem. 2015, 11, 174–183, doi:10.3762/bjoc.11.18
- adopt a Z-configuration. Accordingly, the products of type 2 are formed in high selectivity in terms of regio- and diastereomeric control. The starting materials of type 1 were generated from the aromatic aldehydes and allyltriphenylphosphonium bromide in a Wittig reaction following a known protocol [53
NAA-modified DNA oligonucleotides with zwitterionic backbones: stereoselective synthesis of A–T phosphoramidite building blocks
Beilstein J. Org. Chem. 2015, 11, 50–60, doi:10.3762/bjoc.11.8
- synthesis of both 6'-epimers of nucleosyl amino acid 9 has been reported before. We have used 3-(N-BOM)-protected thymidine-5'-aldehyde 10 (BOM = benzyloxymethyl), which can readily be obtained from thymidine, in a sequence of Wittig–Horner reaction, asymmetric hydrogenation of the resultant didehydro
- corresponding uridine-derived nucleosyl amino acids, we have found that uracil protection was not advantageous for the aforementioned reaction sequence [48]. We have therefore decided to employ both the 3-(N-BOM)-protected thymidine-5'-aldehyde 10 and also its thymine-unprotected congener 11 in Wittig–Horner
- stability, thymidine-5'-aldehydes 10 and 11 were not stored, but directly used for the subsequent Wittig–Horner reaction. They were therefore converted with glycine-derived phosphonate 12 [51][52][53][54] in the presence of potassium tert-butoxide as a base. As anticipated [47][48][55], these reactions
Formal total syntheses of classic natural product target molecules via palladium-catalyzed enantioselective alkylation
Beilstein J. Org. Chem. 2014, 10, 2501–2512, doi:10.3762/bjoc.10.261
- was crossed with methyl vinyl ketone in 62% yield [34]. Reduction of enone 34 was achieved in the presence of Pd/C with H2 in EtOAc to furnish diketone 35 [34]. Chemoselective Wittig mono-olefination of 35 provided ω-enone (−)-32, spectroscopically identical to the material in Danishefsky’s racemic
Indium-mediated allylation in carbohydrate synthesis: A short and efficient approach towards higher 2-acetamido-2-deoxy sugars
Beilstein J. Org. Chem. 2014, 10, 2230–2234, doi:10.3762/bjoc.10.231
- makes use of readily accessible pentoses and hexoses, which are subjected to indium-mediated two-carbon chain elongation. Subsequent ozonolysis and treatment with base yields α,β-unsaturated aldehydes, which are stereoselectively epoxidized using Jørgenson’s protocol. After Wittig chain elongation the
- decomposition of these labile compounds. Conversion of the carbonyl moiety to an acetal group followed by treatment with azide nucleophiles also failed to yield any desired products. Therefore we decided to mask the aldehyde as an olefin. A Wittig reaction with methyl (triphenylphosphoranylidene)acetate (Ph3P
Photochemical approach to functionalized benzobicyclo[3.2.1]octene structures via fused oxazoline derivatives from 4- and 5-(o-vinylstyryl)oxazoles
Beilstein J. Org. Chem. 2014, 10, 2222–2229, doi:10.3762/bjoc.10.230
- .10.230 Abstract Novel cis/trans-4- and cis/trans-5-(2-vinylstyryl)oxazoles have been synthesized by Wittig reactions from the diphosphonium salt of α,α’-o-xylene dibromide, formaldehyde and 4- and 5-oxazolecarbaldehydes, respectively. In contrast, trans-5-(2-vinylstyryl)oxazole has been synthesized by
- /trans-Isomers of 4- and 5-oxazole derivatives (1, 2) were synthesized by Wittig reactions from the diphosphonium salt of α,α’-o-xylene dibromide, formaldehyde and oxazole-4- and 5-carbaldehydes (3, 4), respectively, in absolute ethanol with sodium ethoxide as a base (Scheme 1). The procedure of this
- isocyanide (TosMIC) [38][39]. For the preparation of 5-(2-vinylstyryl)oxazole (2) by this method 3-(2-vinylphenyl)acrylaldehyde (6) was needed. This new o-substituted phenylacrylaldehyde 6 was prepared using (formylmethylene)triphenylphosphorane by a Wittig reaction from o-vinylbenzaldehyde (5). The yield of
Chiral phosphines in nucleophilic organocatalysis
Beilstein J. Org. Chem. 2014, 10, 2089–2121, doi:10.3762/bjoc.10.218
- enantioselectivity. In a relatively successful example, the chiral aminophosphine G9 catalyzed the asymmetric double-Michael reaction between o-tosylamidophenyl malonate and 3-butyn-2-one to give the indoline derivative in 69% yield and up to 10% ee (Scheme 53). 2.15 Annulation through tandem Michael addition/Wittig
- olefination In 2009, Tang and Zhou developed an annulation through tandem Michael addition/Wittig olefination, mediated by the chiral phosphine BIPHEP, for the synthesis of optically active cyclohexa-1,3-diene derivatives (Scheme 54) [97]. Although this reaction required a stoichiometric amount of chiral
Palladium-catalysed cyclisation of alkenols: Synthesis of oxaheterocycles as core intermediates of natural compounds
Beilstein J. Org. Chem. 2014, 10, 2077–2086, doi:10.3762/bjoc.10.216
- –Wadsworth–Emmons olefination of aldehyde 15 furnished the corresponding separable mixture of Z and E alkenes 16 and 17. In the case of utilising stabilised phosphorane ylides, the Wittig reaction provided only Z alkenes 18 and 19. Following acidic hydrolysis provided α-O-benzyl substrates 20–23 in good
- yields. Additionally, the synthesis of substrate 30 with 1,1-disubstituted C–C double bond was accomplished in 3 steps. The addition of methylmagnesium chloride to previously prepared threose 15, followed by Dess–Martin oxidation of the secondary alcohol gave methylketone 29. Subsequent Wittig
Five-membered ring annelation in [2.2]paracyclophanes by aldol condensation
Beilstein J. Org. Chem. 2014, 10, 2021–2026, doi:10.3762/bjoc.10.210
- compounds 2 we previously prepared precursors such as 5 (easily available by Wittig–Horner reaction of the appropriate bis-formyl cyclophanes) and subjected them to catalytic hydrogenation followed by a double Friedel–Crafts cyclization. However, it appeared to us that a more direct route to these useful
Application of cyclic phosphonamide reagents in the total synthesis of natural products and biologically active molecules
Beilstein J. Org. Chem. 2014, 10, 1848–1877, doi:10.3762/bjoc.10.195
- ‘typical’ Wittig and Horner–Wadsworth–Emmons reagents were screened. In addition, cyclic phosphonamides were utilized as olefination reagents (Table 1). Employing phosphonamides 24e and 77 in the olefination of 72 favored the formation of the desired E-isomer of 73a, however the mixture of isomers was
- sequence as shown in Scheme 10. Replacing phosphonamide 79 with Wittig-reagent 80 as olefinating reagent gave a separable E/Z mixture in a ratio of 1:9 in favor of the desired Z-isomer of 73b (Table 1, entry 5). The latter was then transformed into Z-9 in an analogous fashion as described for the E-isomer
- ]. Kishi and co-workers adopted a convergent approach to fumonisin B2, with the molecule being cleaved into three main fragments 103–105 [45][46]. The connection of 103 and 104 under formation of the fumonisin backbone would employ a Wittig reaction, followed by attachment of two molecules of
Multicomponent reactions in nucleoside chemistry
Beilstein J. Org. Chem. 2014, 10, 1706–1732, doi:10.3762/bjoc.10.179
- group has developed the synthesis of D-glucopyranose-derived counterparts of compounds 25 and 26 [73]. The formation of an intermediate imine from a sugar azide and an aldehyde by Staudinger/aza-Wittig reaction was the key step of the synthesis. 2. The Kabachnik–Fields reaction The Kabachnik–Fields
Triazol-substituted titanocenes by strain-driven 1,3-dipolar cycloadditions
Beilstein J. Org. Chem. 2014, 10, 1630–1637, doi:10.3762/bjoc.10.169
- functionalization through the strain-driven 1,3-dipolar cycloaddition with cyclooctyne. The original conditions of Wittig [36], the reaction of cyclooctyne with phenyl azide, and the numerous applications pioneered by Bertozzi suggest that the reaction proceeds under mild conditions [34][35][37][38][39][40
Streptopyridines, volatile pyridine alkaloids produced by Streptomyces sp. FORM5
Beilstein J. Org. Chem. 2014, 10, 1421–1432, doi:10.3762/bjoc.10.146
- synthesized by Wittig reaction using different conditions (Scheme 1). A Wittig–Schlosser reaction [15] starting from a commercially available 5:1 E/Z-mixture of 1-bromobut-2-ene (17) led to preferentially (1E)-configured products. After conversion of 17 into the respective Wittig salt 18 and reaction with 2
- compound. The minor product isolated pure under these conditions was 2-((1Z,3E)-penta-1,3-dienyl)pyridine (9, streptopyridine B), indicated by the coupling constants 3J1,2 = 11.8 Hz and 3J3,4 = 15.1 Hz. To delineate the stereochemistry of the other two isomers 10 and 11, the conditions of the Wittig
- the diastereomeric mixture of Wittig salts. Conclusively, 10 must be the last possible 1Z,3Z-stereoisomer. Both compounds 10 and 11 could not be isolated in pure form, but their mass spectra and retention times were identical to those of the natural products. The mass spectrum of compound 8 indicated
Rasta resin–triphenylphosphine oxides and their use as recyclable heterogeneous reagent precursors in halogenation reactions
Beilstein J. Org. Chem. 2014, 10, 1397–1405, doi:10.3762/bjoc.10.143
- ; polymer-supported reagent; rasta resin; triphenylphosphine oxide; Introduction One of the major drawbacks of the Wittig [1] and Mitsunobu [2][3] reactions is that they result in the formation of a stoichiometric quantity of triphenylphosphine oxide (1) as a byproduct. From an atom economy perspective
- reagents and catalysts [27][28][29][30][31][32][33], and have used easily synthesized rasta resin–Ph3P (14) in various Wittig reactions that required only filtration and solvent removal for product purification (Figure 1) [27][28][29]. Additionally, 14 was converted into phosphonium salt 15, which proved
- previously used as a bifunctional reagent in one-pot Wittig reactions [29]. Gel-phase 31P NMR spectroscopic analysis of 18 indicated that oxidation of the phosphine groups was complete, and elemental analysis was used to determine the loading level of phosphine oxide and amine groups to be 1.07 mmol/g and
Synthesis of a sucrose dimer with enone tether; a study on its functionalization
Beilstein J. Org. Chem. 2014, 10, 1246–1254, doi:10.3762/bjoc.10.124
- two sucrose units. This type of dimers may be eventually used for the construction of macrocycles by (simple) connecting their C-6’ (fructose) ends. Results and Discussion Coupling of two sugar units can be performed by a number of methods. The best one in our hands was the Wittig-type methodology
- 3. First, aldehyde 7 was converted into olefin 15 by treatment with the simplest Wittig reagent: Ph3P=CH2. Subsequent osmylation of the double bond in 15 provided two stereoisomeric diols in a 1:1 ratio; the first one was identical in all respects with the diol obtained from degradation of 11. The
- C75H86NO14Si [M + NH4]+: 1252.5818; found: 1252.5819. Examples of sucrose-based macrocycles. Synthesis of higher sugar precursors by a Wittig-type methodology. CD spectra of in situ formed chiral complexes of 13 (green line), 14 (purple line) and 16 (blue line) with dimolybdenum tetraacetate recorded in DMSO
Amino acid motifs in natural products: synthesis of O-acylated derivatives of (2S,3S)-3-hydroxyleucine
Beilstein J. Org. Chem. 2014, 10, 1135–1142, doi:10.3762/bjoc.10.113
- investigated, but resulted in a moderate yield of 32% only (reaction not displayed). One-pot Swern oxidation to the corresponding aldehyde and subsequent Wittig reaction with stabilized Wittig reagent 32 led to α,β-unsaturated ester 33 in 85% yield. After simultaneous reduction of the double bond and cleavage
Stereocontrolled synthesis of 5-azaspiro[2.3]hexane derivatives as conformationally “frozen” analogues of L-glutamic acid
Beilstein J. Org. Chem. 2014, 10, 1114–1120, doi:10.3762/bjoc.10.110
- synthetic feasibility of approach b), namely the cyclopropanation of the corresponding terminal olefin derivative 18. To explore this alternative approach, we managed to prepare the ethylidene derivative 18 by using either the Wittig or the Tebbe olefination reaction [34][35][36][37]. The former reaction
Structure elucidation of female-specific volatiles released by the parasitoid wasp Trichogramma turkestanica (Hymenoptera: Trichogrammatidae)
Beilstein J. Org. Chem. 2014, 10, 767–773, doi:10.3762/bjoc.10.72
- position 2 underwent ca. 6% epimerization to yield 7 as a mixture of 4 stereoisomers. The synthesis of 2,6,8,12-tetramethyltrideca-2,4-diene (8) was completed by Wittig reaction using (3-methylbut-2-en-1-yl)triphenylphosphonium bromide [15]. As expected, the obtained mixture of all possible stereoisomers
- , followed by oxidation, yielded the aldehyde 10, which was chain elongated by Wittig reaction with [(2E)-1-methylbut-2-en-1-yl]triphenylphosphonium bromide [17] to afford the protected dienol 11 as a mixture of 4 racemates. This was due to partial epimerization at position 2 of the aldehyde 10 and the less
- selective Wittig coupling. Consequently, hydrogenation of 11 yielded a mixture of all 8 possible stereoisomers of the saturated alcohol 12; for relative proportions, see Supporting Information File 1. Starting from 12 and following the sequence described for the transformation of 6 to 8, a mixture of the
Asymmetric total synthesis of a putative sex pheromone component from the parasitoid wasp Trichogramma turkestanica
Beilstein J. Org. Chem. 2014, 10, 761–766, doi:10.3762/bjoc.10.71
- the reduction of 13 with DIBALH is a clean reaction, affording essentially pure 2 after work-up, the preparation of pure 13 was highly desirable. A stepwise olefination approach was therefore considered. Wittig reaction of aldehyde 11 with phosphorane 14 to give 15 was carried out first (Scheme 4) [27
- account for the observed 1H NMR signals. As the Wittig reaction of 11 did afford 15, although with the simultaneous formation of an inseparable side-product, we were curious to see how the analogous Horner–Wadsworth–Emmons olefination towards 15 would perform. Thus, aldehyde 11 was freshly prepared and
- intermediate, leading to a mixture of double bond isomers. The impurity previously observed as a result of the Wittig reaction was not present. In addition, the E- and Z-isomers could be separated using column chromatography affording pure E-15 in 45% yield. Reduction of 15 was achieved using DIBALH, affording
Synthesis of (2S,3R)-3-amino-2-hydroxydecanoic acid and its enantiomer: a non-proteinogenic amino acid segment of the linear pentapeptide microginin
Beilstein J. Org. Chem. 2014, 10, 667–671, doi:10.3762/bjoc.10.59
- ]. While targeting the synthesis of 2a, the Wittig olefination of 3a with n-hexyltriphenylphosphonium bromide and t-BuOK gave olefin 4a as a diasteromeric mixture of Z and E-isomers in the ratio 9.5:0.5 as shown by 1H NMR of the crude product. The catalytic hydrogenation of alkene 4a with 10% Pd/C in
- -pentodialdo-1,4-furanose (3b) which was obtained from D-glucose in good yield as reported earlier [33]. Thus, the Wittig reaction of 3b followed by hydrogenation (10% Pd/C) gave 4-heptyl-D-threose derivative 5b (Scheme 3). Hydrolysis of 1,2-O-isopropylidene (TFA:H2O) followed by oxidative cleavage of the
Synthesis of complex intermediates for the study of a dehydratase from borrelidin biosynthesis
Beilstein J. Org. Chem. 2014, 10, 634–640, doi:10.3762/bjoc.10.55
- allylation as well as an anti-selective aldol reaction. Reference compounds representing the E- and Z-configured double bond isomers as potential products of the dehydratase reaction were obtained from a common precursor aldehyde by Wittig olefination and Still–Gennari olefination. The final deprotection of
- should be accessible from aldehyde 11 through a Horner–Wadsworth–Emmons reaction and the Still–Gennari olefination as well as by a Wittig olefination with stabilised phosphoranes, respectively. The aldehyde 11 should be accessible from the known molecule 13 via 12 [15]. Synthesis of the common precursor
- . Synthesis of reference compounds We exploited a Wittig reaction with a suitable stabilized phosphorane for the synthesis of (E,E)-diene 6a (Scheme 4). The Wittig compound 24 was obtained in two steps from 2-bromopropionic acid following synthetic procedures described for its acetic acid analogue and the
Isocyanide-based multicomponent reactions towards cyclic constrained peptidomimetics
Beilstein J. Org. Chem. 2014, 10, 544–598, doi:10.3762/bjoc.10.50
- products were obtained in excellent yields and in high diastereoselectivity when chiral imines were employed (159b, de >95%). The group of van Boom and Overkleeft reported pipecolic amides via a Staudinger–Aza-Wittig/Ugi sequence (SAWU 3CR, Scheme 51) [132]. First the Staudinger reaction between an
Deoxygenative gem-difluoroolefination of carbonyl compounds with (chlorodifluoromethyl)trimethylsilane and triphenylphosphine
Beilstein J. Org. Chem. 2014, 10, 344–351, doi:10.3762/bjoc.10.32
- . Conclusion: Similar to many other Wittig-type gem-difluoroolefination reactions in the presence of PPh3, the reaction of TMSCF2Cl with aldehydes and activated ketones is effective. Keywords: (chlorodifluoromethyl)trimethylsilane; difluorocarbene; gem-difluoroolefin; organo-fluorine; Wittig reaction; ylide
- -difluoroolefination of carbonyl compounds [17][18]. Among these methods, the latter one has been studied with several named reactions, for example Wittig, Horner–Wadsworth–Emmons, and Julia–Kocienski reactions. In the Wittig gem-difluoroolefination, the reaction is believed to proceed via an undetected
- prepare the ylide intermediate (Scheme 1, reaction 2) [22][23]. Although the difluorocarbene/phosphine procedure for Wittig olefination has been put forward by Fuqua et al. as early as 1964 [19], the formation of difluoromethylene phosphonium ylide in such a way is quite rare [24][25][26]. Established
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