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1.
[formula: see text] A new synthetic strategy for a functionalized tricyclic core of phorbol has been developed by means of a [4 + 3] oxyallyl cycloaddition and subsequent intramolecular Heck reaction. The [4 + 3] oxyallyl cycloadduct 7 was chosen as the B-ring precursor of phorbol. Subsequent elaboration took advantage of its well-defined diastereofacial bias to afford the tricycle 5. This method should be of general value in the construction of 6,7- or 5,7-fused bicyclic systems. 相似文献
2.
A chiral Lewis acid-catalyzed highly enantioselective [4 + 3] cycloaddition reaction of allenamide-derived nitrogen-stabilized chiral oxyallyl cations is described here. The use of bisoxazoline ligand and CuOTf2 provides high enantioselectivity, especially with [SbF6]- as the counteranion. 相似文献
3.
Efforts toward achieving a practical and diastereoselective intramolecular [4+3] cycloaddition of nitrogen-stabilized oxyallyl cations with tethered dienes are described. Epoxidation of N-sulfonyl substituted allenamides with dimethyldioxirane (DMDO) generates nitrogen-stabilized oxyallyl cations that readily undergo stereoselective [4+3] cycloaddition with dienes. Selectivity is found to depend on the tethering length as well as the stability of the oxyallyl cation intermediate, whether generated from N-carbamoyl- or N-sulfonyl-substituted allenamides. The use of chiral N-sulfonyl-substituted allenamides provided minimal diastereoselectivity in the cycloaddition, while high diastereoselectivity can be achieved with a stereocenter present on the tether. These studies provide further support for the synthetic utility of allenamides. 相似文献
4.
Xiong H Huang J Ghosh SK Hsung RP 《Journal of the American Chemical Society》2003,125(42):12694-12695
The first intramolecular [4 + 3] cycloaddition reaction using nitrogen-stabilized chiral oxyallyl cations that are tethered to furan or diene through the nitrogen atom is described here. Formation of these nitrogen-stabilized chiral oxyallyl cations is achieved by a chemoselective epoxidation of chiral allenamides via syringe pump addition of dimethyl dioxirane. The ensuing cycloaddition can be carried out with a range of different lengths for the tether, and high diastereoselectivities can be obtained when using chiral allenamides with shorter tethers. 相似文献
5.
8-Phosphabicyclo[3.2.1]octanes—III4: The reaction between oxyallyl cations and phosphole derivatives
The reaction of oxyallyl cations with phosphole sulfide as well as phosphole oxides was investigated and was found to give the expected 8-phosphabicyclo[3.2.1]octanic system (2, 4 and 7) apart from other unexpected products (3 and 5). In the case of the phosphole sulfide (1), the oxyallyl cation is believed to react preferentially with the P=S group, rather than the dienic moiety, leading to a P=S to P=O transformation or to a very particular reaction resulting in 5. This occurs through an intermediate (j) in which a C=S group reacts in a [2 + 4] cycloaddition with the phosphole as a diene. The structure and stereochemistry of the various products were established by the aid of their spectral data in conjunction with spectral data of some related compounds. A formal PhPO elimination is believed to occur through an intermediate phosphinate resulting from Bayer-Villiger like oxidation, which then loses the [PhPO2] group.Phosphole sulfide (1), previously found to react as a dienophile, was shown to enter a [2 + 4] cycloaddition as a diene with powerful dienophiles like 4-methyl-1,2,4-triazoline-3,5-dione (10). 相似文献
6.
[structure: see text]. A highly stereoselective [4 + 3] cycloaddition of N-substituted pyrroles with allenamide-derived nitrogen-stabilized chiral oxyallyl cations is described here. This method provides an approach for constructing tropinone alkaloids. 相似文献
7.
A concise [4+3] cycloaddition reaction of pyrroles with 2-(silyloxy)allyl cations has been developed. The oxyallyl cations stabilized with a methylthio group or geminal methyl groups were generated from the corresponding allylic alcohols under the influence of a Brönsted acid (Tf2NH), respectively. The use of N-nosyl-protected pyrroles as the four-carbon unit was found to give tropinone derivatives in high yield. 相似文献
8.
Rameshkumar C Xiong H Tracey MR Berry CR Yao LJ Hsung RP 《The Journal of organic chemistry》2002,67(4):1339-1345
Two epoxidations of chiral allenamides are described here. While treatment with m-CPBA led to highly stereoselective formation of an alpha-keto aminal that can be useful synthetically, DMDO oxidation led to conclusive evidence for both nitrogen-substituted allene oxide (via mono-epoxidation) and spiro-epoxide (via bis-epoxidation) using intramolecular nucleophilic trapping experiments. NMR studies provide reliable evidence for a 3-oxetanone that can be derived from the spiro-epoxide and also suggest the presence of an allene oxide. Despite a facile second epoxidation as evidenced by the predominant formation of the 3-oxetanone, in the presence of furan, [4 + 3] cycloaddition of the nitrogen-substituted allene oxide or oxyallyl cation with furan occurs faster than the second epoxidation efficiently leading to cycloadducts. This rate difference plays an invaluable role for the success of a stereoselective sequential epoxidation-[4 + 3] cycloaddition reaction via DMDO epoxidations of chiral allenamides. 相似文献
9.
A cascade carbonylative ring expansion and [2+2]/[4+2] cycloaddition of strained 1-iminylphosphirane complexes with aryl allenes were reported.The carbonylative ring expansion of 1-iminylphosphirane complexes provides an azaphosphacyclohexone complex intermediate with a C=P double bond.The following [2+2] or dearomatic [4+2] cycloaddition of this intermediate with allenes is modulated by the aryl substituents on the imino carbon.The regioselective [2+2] cycloaddition with 1,1-diarylallene provides an entry to bicyclo[4.2.0]octan-4-one skeletons featuring a four-membered phosphacyclobutane moiety.While dearomatic [4+2] cycloaddition was preferred with less aromatic naphthalene and yielded octahydrochrysene skeleton containing heteroatoms. 相似文献
10.
A synthesis of Methylated Epoxyhydroazulenones by Intramolecular [4 + 3] Cycloaddition of an Oxyallyl Intermediate, Generated from 1,1-Dichloro-6-(3-methyl-2-furyl)hexan-2-one (Z)-3-Methylpent-2-en-4-yn-1-ol ( 7 ) was transformed to 2-(4-chlorobutyl)-3-methylfuran ( 4b ) and 2-(but-3-enyl)-3-methylfuran ( 10a ) by C-alkylation and 5-exo-dig cyclization. The Grignard derivative formed from 4b gave 1,1-dichloro-6-(3-methylfur-2-yl)hexan-2-onc ( 1b ) on reaction with dichloroacetyl chloride. This dichloromethyl ketone undergoes a base-induced cyclization to form diastereoisomeric 7-chloro-1,2,3,6,7,8a-hexahydro-4-methyl-8H-3a,6-epoxyazulen-8-ones ( 3bα and 3bβ ) by way of an intramolecular [4+3] cycloaddition of an oxyallyl intermediate 2b. By dechlorination and hydrogenation of 3bβ , the tricyclic hydroepoxyazulenones 18 and 19 have been synthesized. 相似文献
11.
An interesting phosphine-containing Lewis base catalyzed highly regioselective [3 + 2] cycloaddition and a novel nitrogen-containing Lewis base catalyzed highly geometric selective [4 + 2] cycloaddition of isatin derived α,β-unsaturated diesters with α-allenic ester have been disclosed to give the corresponding cyclic products in good to excellent yields under mild conditions. A plausible reaction mechanism has also been proposed on the basis of previous literature and our own investigation. 相似文献
12.
A novel tandem Pd-catalyzed cross-coupling and [4 + 4] cycloaddition sequence allows the rapid synthesis of eight-membered carbocycles starting from alpha-bromovinyl arenes and propargyl bromides in one reaction vessel. It is noteworthy that four components are assembled into one molecule via this procedure. In contrast to alpha-bromovinyl arenes, alpha-bromovinyl alkanes afforded tandem cross-coupling and homo [4 + 2] cycloaddition products. Subjecting an equimolar mixture of alpha-bromostyrene and 2-bromo-1-octene to propargyl bromides furnished the tandem Pd-catalyzed cross-coupling and hetero [4 + 2] cycloaddition product. Exposure of equimolar mixtures of alpha-bromovinyl arenes to allenylindium resulted in tandem a Pd-catalyzed cross-coupling and hetero [4 + 4] cycloaddition products. Synthesis of vinylallene from the reaction of vinyl triflate with allenylindium followed by Pd-catalyzed carbon monoxide insertion reaction gave the corresponding 3,7-nonadienone product via tandem Pd-catalyzed cross-coupling and [4 + 4 + 1] annulation. Tandem Pd-catalyzed cross-coupling, [4 + 4] cycloaddition, and [4 + 2] cycloaddition provided the rapid synthesis of bicyclo[6.4.0]dodecene derivatives starting from alpha-bromovinyl arenes, propargyl bromides, and dienophiles in one operation, in which five components were integrated into one molecule. 相似文献
13.
Vassilikogiannakis G Margaros I Montagnon T Stratakis M 《Chemistry (Weinheim an der Bergstrasse, Germany)》2005,11(20):5899-5907
Biomimetic syntheses of the litseaverticillols A-G, I and J are reported herein. The syntheses rely heavily on the application of two different modes of reaction for photochemically generated singlet oxygen, namely, the [4+2] cycloaddition of singlet oxygen (1O2) with furans and the ene reaction of 1O2 with double bonds. The highlight of these syntheses is a one-pot cascade sequence, involving five synthetic operations initiated by a [4+2] reaction, to form the fully functionalised litseaverticillol core. A series of regioselective ene reactions are then used to appositely functionalise the side chains. The synthesis of litseaverticillol E (both its originally proposed and its actual structures) allows a structural reassignment of this natural product. 相似文献
14.
Greco GE Gleason BL Lowery TA Kier MJ Hollander LB Gibbs SA Worthy AD 《Organic letters》2007,9(19):3817-3820
Carbon dioxide undergoes a Pd-catalyzed [3+2] cycloaddition with trimethylenemethane (TMM) under mild conditions (1 atm, 75 degrees C, 30 min) to produce a gamma-butyrolactone product in 63% yield, when the Pd-TMM complex is generated from 2-(acetoxymethyl)-3-(trimethylsilyl)propene. The reaction reported here is more rapid than the all-carbon [3+2] cycloaddition, and only the gamma-butyrolactone is produced in a competition experiment. With substituted substrates, the reaction is completely regioselective, producing the product derived from the kinetic Pd-TMM complex. 相似文献
15.
N. A. Keiko T. A. Kuznetsova L. I. Larina Yu. A. Chuvashev T. A. Klepikova L. V. Sherstyannikova 《Russian Journal of Organic Chemistry》2006,42(10):1421-1425
Conditions were found for the preparation of 2-ethoxyprop-2-enal dimethylhydrazone by reaction of 2-ethoxypropenal with N,N-dimethylhydrazine. 2-Ethoxyprop-2-enal dimethylhydrazone reacted with methyl vinyl ketone and methyl acrylate according to the [4 + 2]-cycloaddition pattern with regioselective formation of substituted tetrahydropyridines. The major product in the reaction of 2-ethoxyprop-2-enal dimethylhydrazone with 1,4-benzoquinone was 5-hydroxy-1-benzofuran-2-carbaldehyde dimethylhydrazone formed as a result of [3 + 2]-cycloaddition; a small amount of the corresponding [4 + 2]-cycloaddition product was also obtained. Some spontaneous transformations of the primary cycloaddition products were revealed. 相似文献
16.
Pyrazolo[1,5-a]pyridines as p38 kinase inhibitors 总被引:1,自引:0,他引:1
Stevens KL Jung DK Alberti MJ Badiang JG Peckham GE Veal JM Cheung M Harris PA Chamberlain SD Peel MR 《Organic letters》2005,7(21):4753-4756
[reaction: see text] A convergent synthesis of substituted pyrazolo[1,5-a]pyridines has been achieved either via a regioselective [3 + 2] cycloaddition of N-aminopyridines with alkynes or by thermal cyclization of disubstituted azirines. Subsequent palladium-catalyzed introduction of pyridines or de novo synthesis of pyrimidines affords inhibitors of p38 kinase. 相似文献
17.
[reaction: see text] A regioselective method for the preparation of 1,5-trisubstituted 1H-1,2,3-triazoles via a 1,3-dipolar cycloaddition of 1-trimethylsilylacetylenes with organoazides is described. Immobilization of the azide on REM resin and subsequent cycloaddition afforded a 2 x 2 x 4 x 3 membered 1,5-disubstituted 1H-1,2,3-triazole library with an average purified yield of 68%. 相似文献
18.
Dr. Tatiana Suárez-Rodríguez Prof. Dr. Ángel L. Suárez-Sobrino Prof. Dr. Alfredo Ballesteros 《Chemistry (Weinheim an der Bergstrasse, Germany)》2021,27(24):7154-7159
Gold(I)-catalyzed higher-order [8+2] cycloadditions of 8-aryl-8-azaheptafulvenes 1 with allenamides 2 and ynamides 3 were studied. 1,8-Dihydrocycloheptapyrroles 4 were achieved by a regioselective [8+2] cycloaddition of azaheptafulvenes 1 and allenamides 2 in the presence of (2,4-ditBuC6H3O)3PAuNTf2 as catalyst. Besides, ynamides 3 and 8-aryl-8-azaheptafulvenes 1 , undergo a regioselective [8+2] cycloaddition, to give 2-amido-1,4-dihydrocycloheptapyrroles 7 in the presence of JohnPhosAuNTf2 as catalyst. Both reactions take place with good yields and with a variety of substituents. A plausible mechanism hypothesis suggests a nucleophilic attack of the 8-azaheptafulvene to the gold activated electron rich allene or alkyne moieties of the allenamide and ynamide, respectively. 相似文献
19.
A calix[4]arene derived bis(spirodienone) acts as the 2π component in a cycloaddition reaction with two molecules of 3,5-di-tert-butyl-1,2-benzoquinone in the [2+4] manner leading to macrocycles with a benzodioxin moiety. A theoretical rationalization of the results suggested a sterically encumbered regioselective pathway, which gives sterically crowded products. 相似文献
20.
S. S. Rynin V. I. Faustov S. E. Boganov M. P. Egorov O. M. Nefedov 《Russian Chemical Bulletin》2010,59(6):1099-1109
The cycloaddition reactions of dichlorogermylene GeCl2 to ethylene, buta-1,3-diene, and hexa-1,3,5-triene were studied within the framework of the density functional theory (PBE
and B3LYP density functionals) and by the ab initio CBS-QB3 method. The energy characteristics of the reaction of GeCl2 with ethylene were refined and non-empirical quantum chemical calculations of reaction pathways in the GeCl2 + buta-1,3-diene and GeCl2 + hexa-1,3,5-triene systems were carried out for the first time. It was shown that the [2+1] cycloaddition reactions are
kinetically hindered and thermodynamically unfavorable, while the [4+1] and [6+1] cycloaddition reactions are characterized
by low barriers and result in thermodynamically favorable products. For the [4+1] cycloaddition to buta-1,3-diene and [6+1]
cycloaddition to hexa-1,3,5-triene, the most energetically favorable reaction pathways involve a suprafacial and antarafacial
approach of reactants, respectively. 相似文献