A simple procedure for the one‐pot transformation of 2‐N‐tosylamino diselenides into benzo[b][1,4]selenazines has been established. The data collected indicate that the six‐membered heterocyclic ring is the result of a [4+2] cycloaddition reaction of a transient electron‐poor o‐iminoselenoquinone, acting as diene, with an electron‐rich alkene, performing as dienophile. The key step of the synthesis is a 1,4‐elimination at selenium of a selenolate ion, leading to the generation of the heterodiene, that requires catalytic amounts of copper(II) trifluoromethanesulfonate, for the activation of the selenium‐selenium bond. 相似文献
A ligation strategy based on the Diels–Alder [4+2] cycloaddition for the two‐step activity‐based labeling of endogenously expressed enzymes in complex biological samples has been developed. A panel of four diene‐derivatized proteasome probes was synthesized, along with a dienophile‐functionalized BODIPY(TMR) tag. These probes were applied in a Diels–Alder labeling procedure that enabled us to label active proteasome β‐subunits selectively in cellular extracts and in living cells. We were also able to label the activity of cysteine proteases in cell extracts by utilizing a diene‐derivatized cathepsin probe. Importantly, the Diels–Alder strategy described here is fully orthogonal with respect to the Staudinger–Bertozzi ligation, as demonstrated by the independent labeling of different proteolytic activities by the two methods in a single experiment.相似文献
A systematic investigation of ZnCl2‐catalyzed reactions of enynals with alkenes has been undertaken. Structurally unique propeller‐like products could be obtained under mild conditions. Cyclic o‐quinodimethanes (o‐QDMs) are generated through [4+2] cycloaddition between enynals and alkenes. Both electron‐poor and electron‐rich dienophiles could be used to trap the active intermediate through [4+2] cycloaddition. But [1,5]‐H shift products could also be observed when electron‐rich alkenes were used as dienophile. DFT calculations were performed to understand the reaction mechanism. A competition between the [4+2] cycloaddition and [1,5]‐H shift was proposed for the transformation of cyclic o‐QDMs. The selectivity could be affected by the properties of the substrates.
A pair of isodicyclopentafulvenes that carries an exocyclic phenyl group para-substituted with an aza-15-crown-5 or aza-18-crown-6 ring has been prepared. These molecules ( 5a and 5b ) and their respective NaClO4 ( 11 ) and KSCN ( 12 ) complexes were examined for the extent of π-facial stereoselectivity operational during their Diels-Alder cycloaddition to (Z)-1,2-bis(phenylsulfonyl)ethylene ( 2 ) under conditions of high pressure. Whereas 5a and 5b engage in [4 + 2] condensation with a 2.5–3.1 preference for dienophile capture from the above-plane direction, their complexes show a substantially reduced tendency for doing so (14/13 = 1.2–1.4). However, this response goes contrary to those para-substituent effects previously observed. The linear correlation noted earlier conformed to an increased preference for above-plane cycloaddition to 2 as the para-substituent became progressively more electron-withdrawing. Probable reasons for this seemingly divergent behavior are presented. 相似文献
A novel synthetic protocol for the one‐pot chemo‐ and stereoselective construction of diversely functionalized pyrido[1,2‐a]pyrimidin‐4‐imines via copper(I)‐catalyzed [3+2] cycloaddition/ring‐opening rearrangement/[4+2] cycloaddition/aromatization cascade of sulfonyl azides, alkynes and N‐arylidenepyridin‐2‐amines under mild reaction conditions is reported. In addition, the catalytic activity of copper(I)‐modified zeolite, a recyclable, heterogeneous catalyst is also investigated, which gives improved yield compared to its homogeneous equivalents. 相似文献
A variety of dihydroisobenzofuran derivatives has been prepared in good yields via an interesting sequential reaction consisting of palladium‐catalyzed coupling, propargyl‐allenyl rearrangement, [4+2] cycloaddition and aromatization. A double‐coupling, rearrangement, [4+2] cycloaddition and aromatization process is also described for the synthesis of more complex and diverse structures. 相似文献
Acetylenes undergo the [4+2] cycloaddition to 3,6‐di(pyrrol‐2‐yl)‐1,2,4,5‐tetrazine in the potassium hydroxide/dimethyl sulfoxide or potassium tert‐butoxide/dimethyl sulfoxide systems (80 °C, 2.5–4 h) to afford (after extrusion of the nitrogen molecule from the intermediate) 3,6‐di(pyrrol‐2‐yl)pyridazines in up to 73% yield, while under non‐catalytic conditions this reaction does not take place. This unusual result substantially extends the scope of synthetic application and mechanistic diversity of the Diels–Alder reaction. The step‐wise mechanisms involving the formation of [OH/tetrazine]− or [t‐BuO/tetrazine]− anionic intermediate complexes or cycloaddition of tetrazine to the acetylide anion are considered. 相似文献
A formal gold(I)-catalyzed diastereoselective [4+3] cycloaddition of oxime ethers with imines, consisting of 1,2-alkyl migration under mild reaction conditions, has been developed; this provides facile access to a series of highly substituted trans-pyrrolo[3,4-c]azepines. This reaction is easily scaled up to the gram scale. 相似文献
This account summarizes our recent efforts on the acid-catalyzed [2+2] cycloaddition of silyl enol ethers with α,β-unsaturated esters, giving donor-acceptor (D -A) cyclobutanes and their related reactions. The cycloaddition generally produces multisubstituted cyclobutanes in good yields with high diastereoselectivity. We found that aluminum Lewis acids and triflic imide (Tf2NH) had good catalytic activity. The retro [2+2] cycloaddition proceeded at higher reaction temperatures, and in some cases, diastereoselectivity switching of cycloadducts was observed. A microflow protocol was established for Tf2NH-catalyzed [2+2] cycloaddition. Although the cycloaddition usually requires cryogenic conditions in a batch reactor, the microreactor system enabled the production of D -A cyclobutanes, even at ambient temperature. [2+2] Cycloaddition of allylsilanes and alkyl enol ethers, instead of silyl enol ethers, afforded the corresponding D -A cyclobutanes. 相似文献
The Diels-Alder (DA) reaction is a cycloaddition of a conjugated diene and an alkene (dienophile) leading to the formation of a cyclohexene derivative through a concerted mechanism. As DA reactions generally proceed with a high degree of regio- and stereoselectivity, they are widely used in synthetic organic chemistry. Considering eco-conscious public and governmental movements, efforts are now directed towards the development of synthetic processes that meet environmental concerns. Artificial enzymes, which can be developed to catalyze abiotic reactions, appear to be important synthetic tools in the synthetic biology field. This review describes the different strategies used to develop protein-based artificial enzymes for DA reactions, including for in cellulo approaches. 相似文献
A new [3+2] cycloaddition strategy for the direct synthesis of highly substituted pyrroles from the readily available α‐acylketene dithioacetals (or related substrates) and commercially available propargylamines under mild metal‐free conditions has been developed. In this reaction, the acyl group plays a critical role in driving the conjugate addition of propargylamine and further cyclization to give pyrroles. Furthermore, the wide scope was confirmed by the preparation of 1,2,3,4‐tetrasubstituted pyrroles (60–70% yields) via a formal 1,2‐acyl migrating [3+2] cycloaddition pathway with N‐methylprop‐2‐yn‐1‐amine as the secondary amine component. 相似文献
Chiral N‐heterocyclic carbenes were found to be efficient catalysts for the formal [4+2] cycloaddition reaction of alky(aryl)ketenes and o‐quinone methides to give the corresponding 3,3,4‐trisubstituted 3,4‐dihydrocoumarins in good yields with good diastereoselectivities and excellent enantioselectivities. 相似文献
The preparation of tetrasubstituted isoindolines from three alkyne units, two aldehyde units and a primary amine via three consecutive reactions, two aldehyde‐amine‐alkyne couplings (A3‐couplings) and a final [2+2+2] cycloaddition, in a single synthetic operation, is described. The A3‐couplings are catalyzed by copper bromide and the cycloaddition is catalyzed by Wilkinson’s catalyst. It was found that many catalysts known to be efficient at the cycloaddition step were not suitable when this step was part of the tandem reaction sequence. Wilkinson’s catalyst was found to be unique in its suitability for the overall domino reaction sequence. 相似文献
Mg-catalyzed [4+2] cycloaddition reactions between 2-aminobenzaldehydes and ynones offered an array of 2-arylquinoline motifs merged with a CF3-acyl group. Furthermore, with Mg-catalyzed [4+2] annulation as the key step, DDD107498, DDD102542, and Hit analogues were assembled. Finally, a computational study of the reaction mechanism was conducted. 相似文献
Schemes 1 and 2 are examples of type A compounds in which the groups -N=N- and -CH=CH- are held in a close parallel position. They react with dichloro- and fluorochlorocarbene to form a unique pyrazolidine moiety (3–5) in a formal [2 + 2 + 1] cycloaddition which, despite the substitution pattern, is stable to ionization and hydrolysis according to Bredt's rule. The reaction is considered to start with the addition of the carbenes to the azo group. The azomethine imine thus formed subsequently undergoes a rapid [3 + 2] dipolar cycloaddition with the bridging C=C bond. The different isomers from 3–5 are identified from their NMR spectra. 相似文献
Understanding enzymatic Diels–Alder (DA) reactions that can form complex natural product scaffolds is of considerable interest. Sch 210972 1 , a potential anti‐HIV fungal natural product, contains a decalin core that is proposed to form through a DA reaction. We identified the gene cluster responsible for the biosynthesis of 1 and heterologously reconstituted the biosynthetic pathway in Aspergillus nidulans to characterize the enzymes involved. Most notably, deletion of cghA resulted in a loss of stereoselective decalin core formation, yielding both an endo ( 1 ) and a diastereomeric exo adduct of the proposed DA reaction. Complementation with cghA restored the sole formation of 1 . Density functional theory computation of the proposed DA reaction provided a plausible explanation of the observed pattern of product formation. Based on our study, we propose that lipocalin‐like CghA is responsible for the stereoselective intramolecular [4+2] cycloaddition that forms the decalin core of 1 . 相似文献
Diels-Alder reactions with methyl conjuenate ( 2 ) at room temperature, with methyl E-12-oxo-10-octadecenoate ( 11 ) as dienophile and radical cation catalyzed cycloadditions of 2 are described. 2 is prepared from methyl linoleate by base catalyzed isomerization with sodium dimethylsulfoxide in 90% yield. It undergoes readily Diels-Alder reactions at room temperature in the presence of 1–1.8 equivalents of a Lewis acid and catalytic amounts of iodine to form cycloadducts in 55–90% yield. At 140°C 2 reacts with dimethyl maleate and dimethyl acetylenedicarboxylate to cycloadducts in 86% and 73% yield, respectively. Methyl E-12-oxo-10-octadecenoate ( 11 ) can be combined in a Diels-Alder reaction with the dienes 2-(trimethylsilyloxy)-1,3-butadiene and 2,3-dimethylbutadiene in 69% and 86% yield, respectively. By way of radical cation catalysis 2 undergoes [4+2]-cycloadditions with dienes in high yield. 相似文献