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1.
The Diels-Alder cycloadditions of the alpha-acetoxynitroso dienophile in water are reported. The rapid and high yielding synthesis of structurally diverse 3,6-dihydro-1,2-oxazines complements the straightforward elaboration of aminoalcohols obtained from the alpha-acetoxynitroso derivative in anhydrous medium. A rationale for this solvent-dependent product distribution is proposed.  相似文献   

2.
The hetero Diels-Alder reactions of 2-nitrosotoluene and some representative acylnitrosodienophiles with a selected set of 1,3-dienes were studied under microflow conditions. The main assets of the technology, that is, an accurate control of the reaction parameters and continuous operating, led to an increased efficiency of this reaction.  相似文献   

3.
The treatment of cyclopropanes having donor and acceptor substituents at the vicinal positions on the cyclopropane ring with a Lewis acid readily generates a 1,3-zwitterion, which reacted with allylsilanes to produce cycloadducts and allylic products. It was found that the yield of the cycloadduct depends on the steric demand of the alkyl substituents on the silicon atom.  相似文献   

4.
Described are the first examples of Lewis acid-promoted Diels–Alder reactions of vinylpyridines and other vinylazaarenes with unactivated dienes. Cyclohexyl-appended azaarenes constitute a class of substructures of rising prominence in drug discovery. Despite this, thermal variants of the vinylazaarene Diels–Alder reaction are rare and have not been adopted for synthesis, and Lewis acid-promoted variants are virtually unexplored. The presented work addresses this gap and in the process furnishes increased scope, dramatically higher yields, improved regioselectivity, and high levels of diastereoselectivity compared to prior thermal examples. These reactions provide scalable access to druglike scaffolds not readily available through other methods. More broadly, these studies establish a useful new class of dienophiles that, based on preliminary mechanistic studies, should be amenable to conventional strategies for enantioselective catalysis.

Vinyl-substituted azaarenes are rare and challenging substrates as dienophiles in Diels–Alder reactions; by employing Lewis acid activation, high yielding and highly selective cycloadditions with unactivated dienes are enabled.  相似文献   

5.
Polymer-supported acylnitroso dienophiles were prepared and used in hetero Diels-Alder (HDA) reactions with a variety of dienes. The transient acylnitroso dienophiles were prepared in situ from immobilized hydroxamates, which were attached to solid supports via several linkers each cleavable by different cleavage reagents, and served for the synthesis of both N-unsubstituted and N-derivatized HDA adducts. Model compounds were used to (i) optimize reaction conditions for solid-supported HDA reactions, (ii) evaluate the outcome of the reactions with various dienes, (iii) compare relative reactivities of dienes, and (iv) assess the stability of HDA adducts toward cleavage conditions typically used in solid-phase syntheses. Cleaved products were submitted to biological assays, and the results are reported. The accompanying paper, focused on complementary arylnitroso HDA reactions, includes a comparison of both HDA reactions.  相似文献   

6.
Chiral 1-phosphonodienes bearing a bicyclic (R,R)-1,3,2-dioxaphospholane or a (R,R)-1,3,2-diazaphospholidine auxiliary are potent dienes for asymmetric hetero Diels-Alder reactions. Their reactivity towards model nitroso and azodicarboxylate dienophiles has been studied by means of theoretical chemistry at the B3LYP/6-31G∗∗ level. This model, taking solvent effects into account, allowed us to identify parameters governing the stereoselectivity of this reaction. Our study emphasizes a synergy effect when increasing the steric hindrance of substituents of both partners. This led us to predict high levels of diastereoselectivity for one diene. Accordingly, we have hereby illustrated a convenient and original synthesis of this diene and its cycloadditions with commercially available nitroso and azodicarboxylate dienophiles.  相似文献   

7.
8.
Lewis acids are shown to cleave the carbon-carbon bond of activated aziridines at ambient temperature. The derived metal-coordinated azomethine ylides undergo cycloaddition reactions with electron-rich alkenes. Cyclic alkenes afford products that are formally [4+2] adducts most likely derived from a Mannich-type addition to the ylide, followed by intramolecular Friedel-Crafts alkylation. Alternatively, acyclic alkenes undergo [3+2] cycloaddition to give new pyrrolidine products.  相似文献   

9.
A highly enantioselective and atom-economical [2 + 2] cycloaddition of various alkynes with trifluoropyruvate using a dicationic (S)-BINAP-Pd catalyst has been established. This is the first enantioselective synthesis of stable oxetene derivatives, whose structure has been clarified by X-ray analysis. This catalytic process offers a practical synthetic method for oxetene derivatives (catalyst loading: up to 0.1 mol %), which can serve as novel chiral building blocks for pharmaceuticals and agrochemicals and can also be transformed into a variety of enantiomerically enriched CF(3)-substituted compounds with high stereoselectivity.  相似文献   

10.
The tendency of electron-deficient dithioesters to undergo hetero Diels-Alder cycloadditions is successfully used to generate polymer conjugates between a RAFT-polymerized poly(styrene) and a diene-terminated poly(epsilon-caprolactone).  相似文献   

11.
A highly stereoselective formal inverse electron demand hetero Diels-Alder reaction (HDA) occurs on reaction of 2-aryl-alpha,beta-unsaturated aldehydes with cyclopentadiene. The major pathway for this transformation is shown to be a Lewis acid-catalyzed tandem Diels-Alder reaction/retro-Claisen rearrangement.  相似文献   

12.
A simple and efficient one-pot method for the synthesis of new 2,4-diaryl-1,2,3,4-tetrahydroquinolines using a three-component imino Diels-Alder cycloaddition between trans-isoeugenol or trans-anethole, anilines, and benzaldehyde in the presence of BF3·OEt2 in PEG-400, a green and reusable solvent, has been developed. Also, BF3·OEt2-catalyzed formal [3+2] cycloaddition reaction of trans-isoeugenol or trans-anethole with 1,4-benzoquinone in PEG-400 to give dihydrobenzo[b]furan derivatives has been described.  相似文献   

13.
Jung ME  Ho D  Chu HV 《Organic letters》2005,7(8):1649-1651
[reaction: see text] A high-yielding method is described for the rapid synthesis of very hindered cyclohexenes by the Diels-Alder reaction of hindered silyloxy dienes and dienophiles using the mixed Lewis acid catalyst system (AlBr(3)/AlMe(3)). Thus, reaction of the hindered diene 4 with various substituted enones gave good yields of the expected cycloadducts even though both partners are quite sterically hindered.  相似文献   

14.
The reaction of furan and maleic acid was carried out in several solvents. The endo-adduct was isolated and the structure established by its spectral properties and conversion into known compounds. The adducts of furan with fumaric acid, diethyl fumarate and diethyl maleate are reported.  相似文献   

15.
Lewis acid-promoted cyclizations of heteroatom-substituted enynes have been examined. The reaction of enynes and bearing silicon substituents on an alkyne afforded the halogenated five-membered gamma-lactones and gamma-lactams as the main products. The reaction of substrates and having 2-phosphonoacrylate instead of malonate also gave halogenated five-membered cyclic compounds and as the major products. The cyclized products are highly substituted and potentially useful for further synthetic transformations.  相似文献   

16.
α-Nitrofuran derivatives are studied in Diels-Alder reactions under thermal conditions. In contrast to α-acylfurans, they proved to be efficient dienophiles.  相似文献   

17.
Several fluorinated alkenes were prepared from known ethyl (R)-2-fluoro-4,5-dihydroxyisopropylidine-2-pentenoate (1). The fluoroalkenoates were tested as dienophiles with several dienes and showed cycloaddition only with the very reactive diene, 1,3-diphenylisobenzofuran (5). Fluorobutenolide 2 reacted with 5 to produce the endo-syn adduct 9 in a highly stereoselective manner.  相似文献   

18.
19.
The reaction of N-acetyl perfluoroalkyl substituted 2(1H) pyridones (7) with dimethylacetylenedicarboxylate (DMAD) on neutral alumina under solvent free microwave irradiation conditions extended to undergo an inverse electron demand hetero Diels-Alder reaction, however resulted exclusively in E, Z isomers (3:1) of Michael-type N-adducts (8). The similar reaction in case of 7a under thermal and photochemical conditions also gave the same products.  相似文献   

20.
A Brassard diene analogue was grafted on a modified Merrifield resin and used in a hetero Diels-Alder reaction with various aldehydes or ketones. The reaction gave access to 6-substituted 5,6-dihydropyrones (5a-u). This new immobilized electron-rich diene is more stable than the corresponding native diene, and is a versatile supported reagent.  相似文献   

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