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1.
N,N′,N″-Triacylguanidines and N,N′,N″-tri(alkoxycarbonyl)guanidines were prepared and reduced with borohydride salts in a mixture of tetrahydrofuran and acetic acid to give triacyl and tri(alkoxycarbonyl) orthoamides in yields of 40–85%. However, similar reduction of N,N′,N″-tri(t-butoxycarbonyl)guanidine did not give orthoamide but the aminal di(t-butyl) methylenedicarbamate. 相似文献
2.
Renée L. Beyer Hakan Kandemir Mohan Bhadbhade Ibrahim F. Sengul Chao-wei Leu Daniel Wenholz Naresh Kumar David StC. Black 《Tetrahedron letters》2018,59(51):4483-4486
Acylation reactions of 4,6-dimethoxyindoles with glyoxyloyl chlorides were achieved by the use of graphite powder in 1,2-dichloroethane at reflux. The products were monoketones as a result of decarbonylation, rather than the expected 1,2-diketones. Treatment of these monoketones with base led to their cyclisation and elimination of methanol to afford the novel dipyrrolo[2.3-a:1′,2′,3′-fg]acridin-12(1H)-ones. 相似文献
3.
Satyendra Kumar Pandey 《Tetrahedron letters》2006,47(25):4167-4169
An efficient and short synthesis of (2R,3R)- and (2S,3S)-β-hydroxyornithine 1a-b is described using Sharpless asymmetric dihydroxylation and regioselective nucleophilic opening of a cyclic sulfite as the key steps. 相似文献
4.
Radical-mediated opening of a chiral trisubstituted epoxy alcohol using cp2TiCl furnished the ‘2-methyl-1,3-diol’ moiety with the desired stereochemistry, which led to a total synthesis of (3R,4S,5S,9S)-3,5,9-trihydroxy-4-methylundecanoic acid δ-lactone 1. 相似文献
5.
Nativitat Valls 《Tetrahedron letters》2006,47(22):3701-3705
The first syntheses of (2S,3R)- and (2S,3S)-3-chloroleucine (3-chloro-d-leucines 1 and 2) have been achieved from d-3-hydroxyleucine and allo-d-3-hydroxyleucine, respectively, through the formation of the corresponding N-Cbz β-lactones, followed by a ring opening promoted by lithium chloride and a debenzylation process. 相似文献
6.
Gowravaram Sabitha Sambit Nayak M. Bhikshapathi J.S. Yadav 《Tetrahedron letters》2009,50(38):5428-5429
The first total synthesis of (3S,4R)-dihydroxy-(6S)-undecyl-α-pyranone 1 and total synthesis of (2S,3R,5S)-(−)-2,3-dihydroxytetradecan-5-olide 2 have been achieved in five steps in a highly stereoselective manner using Maruoka allylation, olefin cross-metathesis, and Sharpless asymmetric dihydroxylation as key steps. 相似文献
7.
The single crystals of four kinds of metal nitride halides, β-MNX (M=Zr, Hf; X=Br, I), were prepared in Pt (or Au) capsules by the reaction of MN or α-MNX powders with NH4X as fluxes under a high pressure of 3-5 GPa at 1000-1100°C. Their crystal structures were determined by single-crystal X-ray diffraction techniques. All four compounds crystallize in a rhombohedral space group R-3m, Z=6 with a=3.6403(6) Å, c=29.270(5) Å for β-ZrNBr, a=3.718(2) Å, c=31.381(9) Å for β-ZrNI, a=3.610(1) Å, c=29.294(6) Å for β-HfNBr, and a=3.689(1) Å, c=31.329(6) Å for β-HfNI. β-ZrNBr is isotypic with SmSI and the others are isotypic with YOF. Both structure variants are composed of structural slabs [X-M-N-N-M-X] (M=Zr, Hf; X=Br, I) stacked together by X…X van der Waals forces, but the ways of the layer stacking sequence are different: XAMcNBNCMbXA∣XCMbNANBMaXC∣XBMaNCNAMcXB∣ in the SmSI-type and XAMbNCNBMcXA∣XCMaNBNAMbXC∣XBMcNANCMaXB∣ in the YOF-type polymorphs. 相似文献
8.
An improved synthesis of (S)-7-amino-5H,7H-dibenzo[b,d]azepin-6-one (1), involving a selective crystallization of epimeric menthylcarbamates for the resolution step followed by simultaneous cleavage of the carbamate and the lactam protecting group is described. Epimerization conditions of the undesired epimer have also been determined. 相似文献
9.
Kai Zhang Ji Zhang Lanqi Huang Xiaoqin Zhang Gui Yu Man Shing Wong 《Tetrahedron letters》2018,59(28):2717-2721
A series of novel benzo[2,1-b:3,4-b’]bis[1]-benzothiophene (BBBT) derivatives with different side-chains were synthesized and characterized. And their mobility properties were evaluated based on their active layers in OFETs devices. By means of simple thermal annealing, the devices based on BBBT-4 and BBBT-6 exhibited typical p-type FETs behavior with average hole mobilities of 0.28 and 0.124?cm2 V?1?s?1, respectively. Furthermore, the structure-property relationships of these semiconductors were also investigated by XRD and AFM. 相似文献
10.
Kazuishi Makino 《Tetrahedron》2009,65(45):9468-7372
(2S,3R)- and (2R,3R)-2,3-Diaminobutanoic acid (Dab) derivatives were efficiently synthesized from Cbz-(R)-alanine using the proline-catalyzed diastereoselective α-hydrazination reaction and the SmI2-promoted reductive cleavage of the N-N bond as the key steps. 相似文献
11.
The first asymmetric total synthesis of (R)-tuberolactone, (S)-jasmine lactone and (R)-δ-decalactone
A general synthetic approach has been developed for the first asymmetric total synthesis of tuberolactone 1, jasmine lactone 2 and δ-decalactone 3. The key step is the selective hydrogenation of triple and endocyclic double bonds in the key intermediate 4. 相似文献
12.
Francisco J. Sayago 《Tetrahedron》2009,65(27):5174-5180
High yielding and remarkably selective alkylations of a suitably protected derivative of (2S,3aS,7aS)-octahydroindole-2-carboxylic acid are described. The fused bicyclic structure of this proline analogue greatly influences the stereochemical outcome of direct alkylation reactions taking place at the α-carbon and provides access to α-substituted analogues with retention of the configuration. The overall procedure allows the preparation of enantiopure α-substituted derivatives of this Oic isomer, suitably protected for their incorporation into peptides, in a straightforward manner. 相似文献
13.
Stephen G. Davies Ai M. Fletcher Catherine J. Greenaway Matthew S. Kennedy Christoph Mayer Paul M. Roberts James E. Thomson 《Tetrahedron》2018,74(38):5049-5061
A total of nine enantiopure syn-β-substituted-α-amino acids have been synthesised, comprising both syn-β-hydroxy-α-amino acids and syn-β-fluoro-α-amino acids. The key step in the synthetic strategy towards these syn-β-substituted-α-amino acids involves a stereospecific rearrangement, which proceeds via the intermediacy of the corresponding aziridinium ions. The requisite enantiopure syn-α-hydroxy-β-amino esters were prepared via asymmetric aminohydroxylation of the corresponding α,β-unsaturated esters followed by epimerisation of the resultant anti-α-hydroxy-β-amino esters at the C(2)-position. Subsequent activation of the α-hydroxy moiety as a leaving group followed by displacement by the β-amino substituent gave the corresponding aziridinium species. Regioselective in situ ring-opening of the aziridinium intermediates with either water or fluoride gave the corresponding syn-β-hydroxy-α-amino ester or syn-β-fluoro-α-amino ester, respectively, and N-deprotection and ester hydrolysis afforded the target syn-β-substituted-α-amino acids as single diastereoisomers in good overall yield. 相似文献
14.
Jan Hajduch 《Journal of fluorine chemistry》2008,129(2):112-118
Horner-Emmons fluoroolefination of an aryl aldehyde followed by introduction of a second fluorine via “FBr” addition provides an original approach to the preparation of 1-alkyl-2-aryl-1,2-difluoroethenes. The utility of this procedure is demonstrated by the preparation of (E and Z)-α,β-difluorourocanic acid. 相似文献
15.
Da Young Seo Hwa Jung Roh Hwi Yul Jo Sung Cho Jae Nyoung Kim 《Tetrahedron letters》2018,59(11):1005-1009
cis-N,N′-Dialkylisoindigo derivatives were synthesized for the first time by the reaction of 3-indolyl-2-oxindoles with DDQ in aqueous 1,4-dioxane. cis-Isoindigo derivatives were completely isomerized to the corresponding trans-isomers by heating the solution in short time. 相似文献
16.
Rudolf Knorr Ernst Lattke Jakob Ruhdorfer Kathrin Ferchland Ulrich von Roman 《Tetrahedron》2018,74(14):1621-1631
Common wisdom might anticipate that two methyl groups placed on a molecular migration route should act as an impediment. However, the “conducted tour” migration of Li+(THF)4 across the aryl ring (“π-route”) during the cis/trans stereoinversion of α-arylvinyllithiums had been found to occur with practically equal velocities in the presence of either one or two ortho-alkyl substituents. We now report that the omission of both ortho-methyl groups retards the stereoinversion process. In order to arrive at an answer to the title question, we investigate the aggregation equilibria and microsolvation states of ortho, ortho′-unsubstituted α-lithiostyrenes by means of approved secondary NMR criteria. Beyond such necessary knowledge about the ground-state properties, we provide kinetic evidence showing that the retarded cis/trans stereoinversion of α-lithiostyrene proceeds by the pseudomonomolecular, ionic mechanism with Li+(THF)4 migration. 相似文献
17.
A three-step synthesis of (R)-7-hydroxycarvone (1), which is anticipated to be a valuable building block for the versatile preparation of natural products, is described. Optimization of the reaction conditions for photooxygenation and migration of (S)-α-pinene 2, tetrapropylammonium perruthenate (TPAP) oxidation of the generated alcohol, and a subsequent ring-opening reaction in the presence of Cu(OTf)2 led to the synthesis of 1 with good reproducibility. The desired product 1 was thus obtained in 46% yield over three steps. 相似文献
18.
A new and efficient method for the synthesis of hitherto unreported spiro[benzo[4,5]thiazolo[3,2-a]chromeno[2,3-d]pyrimidine-14,3′-indoline]-1,2′,13(2H)-triones was developed via the Domino Knoevenagel condensation–Michael addition–intermolecular cyclization sequences of isatin derivatives, cyclohexane-1,3-diones, and 2-hydroxy-4H-benzo[4,5]thiazolo[3,2-a]pyrimidin-4-ones, employing 12-tungstophosphoric acid (H3PW12O40) as an effective and inexpensive catalyst. 相似文献
19.
Pintu Kumar Mandal 《Tetrahedron》2008,64(37):8685-8691
Two pentasaccharides containing a common tetrasaccharide (lacto-N-neotetraose) core, and d-galactosamine and N-acetyl neuraminic acid in the non-reducing ends, respectively, corresponding to the lipooligosaccharides of Neisseria gonorrhoeae and Neisseria meningitidis were synthesized in a very concise manner from a common trisaccharide derivative using minimum number of steps. Thioglycosides and glycosyl trichloroacetimidate have been used as glycosyl donors for glycosylations and yields were excellent in every step. 相似文献
20.
A new thiourea linked peracetylated glucopyranosyl–anthraquinone conjugate (L) has been synthesized and characterized. The binding properties of L have been studied with nineteen different anions. The L exhibited selective chromogenic as well as fluorescent chemosensor property toward F− by a ∼13-fold increase in the emission intensity upon binding with F−. The minimal detection limit for F− is 185 ± 5 ppb in acetonitrile. Interaction of F− led to a bathochromic shift of 80 nm in the absorption band. An INHIBIT logic gate has been proposed using the output obtained from the fluorescence studies. The structure of the species formed upon the interaction of F− with L has been established by DFT computations. 相似文献