共查询到20条相似文献,搜索用时 15 毫秒
1.
OrazioA. Attanasi Lucia DeCrescentini Paolino Filippone Francesco Fringuelli Fabio Mantellini Mizio Matteucci Oriana Piermatti Ferdinando Pizzo 《Helvetica chimica acta》2001,84(2):513-525
The cycloadditions of (E)‐3‐diazenylbut‐2‐enes 1 with a variety of alkenes 2 – 6 were carried out in water as well as in organic solvents. The reactions were always faster in heterogeneous aqueous medium than in the organic solvents. These conjugated diazenyl‐alkenes behave mainly as heterodienes, and the Diels‐Alder adducts are the sole or at least main reaction products. Pyrroles derived from zwitterionic [3+2] cycloaddition reactions were observed in some cases. The cycloaddition of 1a with (+)‐2‐(ethenyloxy)‐3,7,7‐trimethylbicyclo[4.1.0]heptane ( 5 ) is the first example of an asymmetric `inverse electron‐demand' Diels‐Alder reaction carried out in pure water. 相似文献
2.
A new total synthesis of the natural carbazole murrayanine ( 1 ) was developed by using the 4,5‐dimethyleneoxazolidin‐2‐one 12 as starting material. The latter underwent a highly regioselective Diels–Alder cycloaddition with acrylaldehyde (=prop‐2‐enal; 13 ) to give adduct 14 (Scheme 3). Conversion of this adduct into diarylamine derivative 9 was carried out via hydrolysis and methylation (Scheme 4). Differing from our previous synthesis, in which such a diarylamine derivative was transformed into 1 by a PdII‐stoichiometric cyclization, this new approach comprised an improved cyclization through a more efficient Pd0‐catalyzed intramolecular diaryl coupling which was applied to 9 , thus obtaining the natural carbazole 1 in a higher overall yield. 相似文献
3.
4‐(Acylamino)‐5‐nitrosopyrimidines react either by a reductive condensation to provide 8‐substituted guanines, or by a Diels–Alder cycloaddition, or an ene reaction, to provide 6‐substituted pteridinones, depending on the nature of the acyl group and the reaction conditions. Experimental details are provided for the transformation of (acylamino)‐nitrosopyrimidines to 8‐substituted guanines, and the scope of the reaction is further demonstrated by transforming the trifluoro acetamide 25 to the 8‐(trifluoromethyl)guanine ( 27 ), and the N,N′‐bis(nitrosopyrimidinyl)‐dicarboxamide 29 to the (R,R)‐1,2‐di(guan‐8‐yl)ethane‐1,2‐diol ( 32 ). An intramolecular Diels–Alder reaction of the N‐sorbyl (=N‐hexa‐2,4‐dienoyl) nitrosopyrimidine 10 , followed by a spontaneous elimination to cleave the N,O bond of the initial cycloaddition product provided the pteridinones 14 or 15 , characterized by a (Z)‐ or (E)‐3‐hydroxyprop‐1‐enyl group at C(6). Treatment of 10 with Ph3P led to the C(8)‐penta‐1,3‐dienyl‐guanine 18 . The ene reaction of the N‐crotonyl (=N‐but‐2‐enoyl) nitrosopyrimidine 19 provided the 6‐vinyl‐pteridinone 20a that dimerized readily to 21a , while treatment of 19 with Ph3P led in high yield to 8‐(prop‐1‐enyl)guanine ( 23 ). The structure of the dimer 21 was established by X‐ray analysis of its bis(N,N‐dimethylformamidine) derivative 21b . The crystal structure of the nitroso amide 10 is characterized by two molecules in the centrosymmetric unit cell. Intermolecular H‐bonds connect the amino group to the amide carbonyl and to N(1). The crystalline bis(purine) 30 forms a left‐handed helix with four molecules per turn and a pitch of 30.2 Å. 相似文献
4.
Tris(9′,10′‐dimethyl[9,10]ethanoanthracene[11′,12′: 1,9;11″,12″: 16,17;11′′′,12′′′: 30,31])[5,6]fullerene C60, the orthogonal (e,e,e)‐tris‐adduct of C60 and 9,10‐dimethylanthracene, was obtained from [4+2]‐cycloaddition (Diels–Alder reaction) at room temperature. The thermally unstable orange red (e,e,e)‐tris‐adduct was purified by chromatography and was isolated in the form of red monoclinic crystals. Its C3‐symmetric addition pattern was established spectroscopically. Its structure could be further investigated by single crystal X‐ray diffraction. The (e,e,e)‐tris‐adduct of C60 and 9,10‐dimethylanthracene has earlier been suggested as intermediate and reversibly formed critical component in ‘template directed’ addition reactions of C60. This previously elusive compound has now been isolated and structurally characterized. 相似文献
5.
Dimethyl acetylenedicarboxylate (DMAD) is a very important and useful reagent for the preparation of dimethyl heterocyclic‐o‐dicarboxylates, which are key intermediates in the synthesis of fused pyridazine derivatives. The synthesis of thiopyranes by the Diels‐Alder reaction of dithiocarboxylate derivatives, synthesis of various cyclazines by [2 + 8] cycloaddition reactions, and synthesis of dimethyl pyrazolo[3,4‐b]pyridine‐5,6‐dicarboxylates and polycyclic heterocycles containing the 1,6‐naphthyridine ring system by the reaction of o‐aminonitrile compounds with DMAD are described here. 相似文献
6.
ValeryN. Kalinin IgorV. Shishkov SergeyK. Moiseev ElviraE. Shults GenrikhA. Tolstikov NataliaI. Sosnina PavelV. Petrovskii KonstantinA. Lyssenko Helmut Schmidhammer 《Helvetica chimica acta》2006,89(5):861-869
In a search for starting materials for the preparation of 7,8‐fused morphine alkaloid derivatives, 8‐[(1E‐2‐phenylethenyl]codeinone dimethyl ketal ( 4 ) and 8‐[(1E‐2‐phenylethenyl]codeine ( 5 ) were prepared. These dienes were used as substrates in the Diels–Alder reactions. Compound 5 formed the ‘normal’ adduct 12 with N‐phenylmaleimide, while compound 4 behaved in reactions with dienophiles as the ‘masked’ diene 11 , a 8‐[(1E)‐2‐phenylethenyl]‐substituted thebaine, yielding the corresponding 19‐substituted 6,14‐endo‐etheno‐6,7,8,14‐tetrahydrothebaines. Specifically, reaction of 4 with methyl vinyl ketone gave rise to 19‐[(1E)‐phenylethenyl]thevinone ( 14 ) whose structure was elucidated by an X‐ray diffraction analysis. The thebaine derivative 11 was also prepared from 4 . 相似文献
7.
Firouz Matloubi Moghaddam Mostafa Kiamehr Salman Taheri Zohreh Mirjafary 《Helvetica chimica acta》2010,93(5):964-973
An efficient synthesis of polycyclic indole derivatives is achieved via domino Knoevenagel–hetero‐Diels–Alder reaction of O‐acrylated salicylaldehyde derivatives with dihydroindole‐2‐thiones in H2O as solvent. The products are formed in good‐to‐excellent yields with high regio‐ and stereoselectivity. 相似文献
8.
Cephalosporin sulfoxides 1 and 2 containing an enone‐ or dienone‐type moiety at position 2 were treated with 2,3‐dimethylbuta‐1,3‐diene or diethyl azodicarboxylate to synthesize, in Diels? Alder reactions, the new cephalosporin derivatives 4 and 5 with a cyclic substituent (Scheme 1). Under the same conditions, ethyl diazoacetate and diazomethane reacted differently: while reactions of 1 and 3 with the former lead to compounds 7 – 10 corresponding to the 1,3‐dipolar cycloaddition route (Scheme 2), diazomethane produced only enol ethers 12 and 13 , respectively (Scheme 3). This difference could be rationalized by assuming two different reaction pathways: an orbital‐symmetry‐controlled concerted cycloaddition and an ionic one. 相似文献
9.
Modulation of Reactivities of Dienophiles for DielsAlder Reactions via Complexation of α,β‐Unsaturated Chelating Amides
下载免费PDF全文
![点击此处可从《Helvetica chimica acta》网站下载免费的PDF全文](/ch/ext_images/free.gif)
We describe the modulation of reactivities of dienophiles for Diels? Alder reactions via a new principle based on chelating amides positioned adjacent to their C?C bond. It is demonstrated for modified acrylic acid derivatives and related dienophiles with three different chelating entities. Complexation of the chelators leads to an intensified electron‐withdrawing effect leading to an enhancement of reactivity in Diels? Alder reactions depending on the complexed metal ion. The application of this new approach might be extended to other reactions with reacting entities adjacent to chelating amides. 相似文献
10.
Basi V. Subba Reddy Nagendra Nath Yadav Nikhil Srivastava Jhillu S. Yadav Balasubramanian Sridhar 《Helvetica chimica acta》2012,95(1):76-86
Ionic liquids were found to be a suitable reaction medium for 1,4‐dipolar cycloaddition reactions of an isoquinoline, an activated alkyne, and a 4‐oxo‐4H‐1‐benzopyran‐3‐carboxaldehyde at room temperature to afford [1]benzopyrano‐pyrido‐isoquinoline (=9aH,15H‐benzo[a][1]benzopyrano[2,3‐h]quinolizine) derivatives selectively in good yields. The ionic liquid can be recovered and recycled in further runs without loss of activity. 相似文献
11.
Elena Roversi Frdric Monnat Pierre Vogel Kurt Schenk Pietro Roversi 《Helvetica chimica acta》2002,85(3):733-760
The reactivity of sulfur dioxide toward variously substituted butadienes was explored in an effort to define the factors affecting the competition between the hetero‐Diels‐Alder and cheletropic additions. At low temperature (<−70°), 1‐alkyl‐substituted 1,3‐dienes 1 that can adopt s‐cis‐conformations add to SO2 in the hetero‐Diels‐Alder mode in the presence of CF3COOH as promoter. In the case of (E)‐1‐ethylidene‐2‐methylidenecyclohexane ((E)‐ 4a ), the [4+2] cycloaddition of SO2 is fast at −90° without acid catalyst. (E)‐1‐(Acyloxy)buta‐1,3‐dienes (E)‐ 1c , (E)‐ 1y , and (E)‐ 1z with AcO, BzO, and naphthalene‐2‐(carbonyloxy) substituents, respectively also undergo the hetero‐Diels‐Alder addition with SO2+CF3COOH at low temperatures, giving a 1 : 10 mixture of the corresponding cis‐ and trans‐6‐(acyloxy)sultines c‐ 2c,y,z and t‐ 2c,y,z , respectively). Above −50°, the sultines undergo complete cycloreversion to the corresponding dienes and SO2, which that add in the cheletropic mode at higher temperature to give the corresponding 2‐substituted sulfolenes (=2,5‐dihydrothiophene 1,1‐dioxides) 3 . The hetero‐Diels‐Alder additions of SO2 follow the Alder endo rule, giving first the 6‐substituted cis‐sultines that equilibrate then with the more stable trans‐isomers. This statement is based on the assumption that the S=O group in the sultine prefers a pseudo‐axial rather than a pseudo‐equatorial position, as predicted by quantum calculations. The most striking observation is that electron‐rich dienes such as 1‐cyclopropyl‐, 1‐phenyl‐, 1‐(4‐methoxyphenyl)‐, 1‐(trimethylsilyl)‐, 1‐phenoxy‐, 1‐(4‐chlorophenoxy)‐, 1‐(4‐methoxyphenoxy)‐, 1‐(4‐nitrophenoxy)‐, 1‐(naphthalen‐2‐yloxy)‐, 1‐(methylthio)‐, 1‐(phenylthio)‐, 1‐[(4‐chlorophenyl)thio]‐, 1‐[(4‐methoxyphenyl)thio]‐, 1‐[(4‐nitrophenyl)thio]‐, and 1‐(phenylseleno)buta‐1,3‐diene, as well as 1‐(methoxymethylidene)‐2‐methylidenecyclohexane ( 4f ) do not equilibrate with the corresponding sultines between −100 and −10°, in the presence of a large excess of SO2, with or without acidic promoter. The hetero‐Diels‐Alder additions of SO2 to 1‐substituted (E)‐buta‐1,3‐dienes are highly regioselective, giving exclusively the corresponding 6‐substituted sultines. The 1‐substituted (Z)‐buta‐1,3‐dienes do not undergo the hetero‐Diels‐Alder additions with sulfur dioxide. 相似文献
12.
Kazuhiro Kobayashi Taketoshi Kozuki Manami Konishi Teruhiko Suzuki Miyuki Tanmatsu Hisatoshi Konishi 《Helvetica chimica acta》2011,94(7):1234-1238
The reaction of aryl(3‐isocyanopyridin‐4‐yl)methanones 1 , easily prepared from commercially available pyridin‐3‐amine, with aryl Grignard reagents gave, after aqueous workup, 2,3‐diaryl‐3H‐pyrrolo[2,3‐c]pyridin‐3‐ols 2 . These rather unstable alcohols were O‐acylated with Ac2O in pyridine in the presence of a catalytic amount of 4‐(dimethylamino)pyridine (DMAP) to afford the corresponding 2,3‐diaryl‐3H‐pyrrolo[2,3‐c]pyridin‐3‐yl acetates 3 in relatively good yields. 相似文献
13.
Martin S. Seyfried Anthony Linden Grzegorz Mlostoń Heinz Heimgartner 《Helvetica chimica acta》2009,92(9):1800-1816
The reactions of 5‐benzylidene‐3‐phenylrhodanine ( 2 ; rhodanine=2‐thioxo‐1,3‐thiazolidin‐4‐one) with diazomethane ( 7a ) and phenyldiazomethane ( 7b ) occurred chemoselectively at the exocyclic C?C bond to give the spirocyclopropane derivatives 9 and, in the case of 7a , also the C‐methylated products 8 (Scheme 1). In contrast, diphenyldiazomethane ( 7c ) reacted exclusively with the C?S group leading to the 2‐(diphenylmethylidene)‐1,3‐thiazolidine 11 via [2+3] cycloaddition and a ‘two‐fold extrusion reaction’. Treatment of 8 or 9b with an excess of 7a in refluxing CH2Cl2 and in THF at room temperature in the presence of [Rh2(OAc)4], respectively, led to the 1,3‐thiazolidine‐2,4‐diones 15 and 20 , respectively, i.e., the products of the hydrolysis of the intermediate thiocarbonyl ylide. On the other hand, the reactions with 7b and 7c in boiling toluene yielded the corresponding 2‐methylidene derivatives 16, 21a , and 21b . Finally, the reaction of 11 with 7a occurred exclusively at the electron‐poor C?C bond, which is conjugated with the C?O group. In addition to the spirocyclopropane 23 , the C‐methylated 22 was formed as a minor product. The structures of the products (Z)‐ 8, 9a, 9b, 11 , and 23 were established by X‐ray crystallography. 相似文献
14.
Gowravaram Sabitha Chittapragada Maruthi ErigalaVenkata Reddy Chitti Srinivas JhilluS. Yadav SamitK. Dutta AjitC. Kunwar 《Helvetica chimica acta》2006,89(11):2728-2731
A novel, efficient synthesis of a series of functionalized, benzo‐annelated decahydrofuro[3,2‐h][1,6]naphthyridine derivatives 3 has been achieved. The protocol is based on the intramolecular hetero‐Diels–Alder (IMHDA) reaction of in situ formed imines derived from an N‐prenylated sugar aldehyde 1 and different aromatic amines 2 in the presence of bismuth(III) chloride as catalyst. The reactions could be run under very mild conditions at room temperature, and were complete within 30 min, affording exclusively and stereoselectively the corresponding trans‐fused products 3 in good‐to‐excellent yields (Table). 相似文献
15.
Ángel M. Montaña Juan A. Barcia Gabriele Kociok‐Köhn Mercè Font‐Bardia Xavier Solans 《Helvetica chimica acta》2008,91(2):187-208
The 3‐aminotropones (=3‐aminocyclohepta‐2,4,6‐trien‐1‐ones) 4 were prepared in two steps by i) a [4+3] cycloaddition reaction between a conveniently substituted α,α′‐dihalo ketone 1 and a furan‐2‐amine derivative 2 functionalized at C(2) by a protected amino group (→ 3 ), and ii) a base‐induced molecular rearrangement of the cycloadduct 3 via cleavage of the O‐bridge. A mechanism for the formation of 3‐aminotropones is proposed on the basis of the initial deprotonation of the [(tert‐butoxy)carbonyl]amino (BocNH) group of 3 , followed by O‐bridge opening, an acid–base equilibrium, and finally an alkoxyaluminate elimination to afford the conjugated stable troponoid system (Scheme 7). 相似文献
16.
An efficient enantioselective synthesis of 3‐acetoxy trans‐β‐lactams 7a and 7b via [2+2] cycloaddition reactions of imines 4a and 4b , derived from a polycyclic aromatic amine and bicyclic chiral acid obtained from (+)‐car‐3‐ene, is described. The cycloaddition was found to be highly enantioselective, producing only trans‐(3R,4R)‐N‐azetidin‐2‐one in very good yields. This is the first report of the synthesis of enantiomerically pure trans‐β‐lactams 7a and 7b with a polycyclic aromatic substituent at N(1) of the azetidin ring. 相似文献
17.
1,3‐Dipolar Cycloadditions of α‐Diazo Ketones Derived from N‐Protected (S)‐Proline with Aromatic and Cycloaliphatic Thioketones
下载免费PDF全文
![点击此处可从《Helvetica chimica acta》网站下载免费的PDF全文](/ch/ext_images/free.gif)
Enantiomerically pure α‐oxo diazo compounds derived from (S)‐proline were used for 1,3‐dipolar cycloaddition with aryl and hetaryl thioketones, as well as with cycloalkanethiones. Whereas the reactions with hetaryl thioketones in boiling THF yield α,β‐unsaturated ketones via a cascade of cycloaddition, 1,3‐dipolar electrocyclization, and desulfurization, the analogous reactions with thiobenzophenone and cycloalkanethiones result in the formation of 1,3‐oxathiole derivatives. In the latter case, the 1,5‐dipolar electrocyclization of the intermediate thiocarbonyl ylide is the key step of the reaction sequence. In all cases, the isolated products are optically active, i.e., the multistep processes occur with retention of the stereogenic center incorporated via the use of (S)‐proline as the precursor of the diazo compounds. 相似文献
18.
Yann Davion Benoît Joseph Valrie Bnteau Jean‐Michel Lger Christian Jarry Jean‐Yves Mrour 《Helvetica chimica acta》2003,86(7):2687-2697
Pyrano[3,2‐b]indole derivatives 2 – 6 were synthesized in good yields from 1‐acetyl‐2‐benzylidene‐2,3‐dihydro‐1H‐indol‐3‐ones 8 and 13 – 15 by an intramolecular hetero‐Diels? Alder reaction. The structures of compounds 2a, 3a, 4, 5 , and 6 were unambiguously established by X‐ray analysis. Compounds 4 and 5 were further aromatized to the corresponding derivatives 16 and 17 , respectively. 相似文献
19.
1‐Thiacyclooct‐4‐yne (=5,6‐didehydro‐3,4,7,8‐tetrahydro‐2H‐thiocin; 9 ) can be prepared from thiocan‐5‐one ( 6 ) in three steps by applying the so‐called selenadiazole method. The heterocyclic alkyne can be oxidized to the corresponding sulfoxide 16 and sulfone 17 . Due to their geometrical strain, all three cyclic alkynes show high reactivities in Diels? Alder and 1,3‐dipolar cycloadditions. Moreover, tetrathiafulvalenes can be prepared from 9 and 16 by the reaction with CS2. 相似文献
20.
The [3,3′(4H,4′H)‐bi‐2H‐1,3‐oxazine]‐4,4′‐diones 3a – 3i were obtained by [2+4] cycloaddition reactions of furan‐2,3‐diones 1a – 1c with aromatic aldazines 2a – 2d (Scheme 1). So, new derivatives of bi‐2H‐1,3‐oxazines and their hydrolysis products, 3,5‐diaryl‐1H‐pyrazoles 4a – 4c (Scheme 3), which are potential biologically active compounds, were synthesized for the first time. 相似文献