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[reaction: see text] 5-(2'-Deoxyuridinyl)methyl radical (1) resulting from formal hydrogen atom abstraction from the methyl group of thymidine is produced from the respective phenyl selenide precursor (2) via 350 nm photolysis or mild thermolysis (37 degrees C in the presence of glutathione) under aerobic or anaerobic conditions. The mild thermal generation of a nucleoside radical provides an alternative to previously reported photochemical methods, which are not always compatible with nucleic acids. 相似文献
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The reaction of dilithium biphenyl (Li2C12H10) with alkyl fluorides has been studied from the point of view of the distribution of products. Two main reaction pathways, the nucleophilic substitution (SN2) and the electron transfer (ET), can compete to yield the same alkylation products in what is known as the SN2-ET dichotomy. SN2 seems to be the main mechanism operating with primary alkyl fluorides (n-RF). Alkylation proceeds in good yields, and the resulting alkylated dihydrobiphenyl anion (n-RC12H10Li) can be trapped with a second conventional electrophile (E+) affording synthetically interesting dearomatized biphenyl derivatives (n-RC12H10E). The reaction gives a higher amount of ET products as we move to secondary (s-RF) and to tertiary alkyl fluorides (t-RF), in which case the mechanism seems to be dominated by ET. In this case, alkylation by radical coupling is still feasible, giving access to the synthesis of t-RC12H10E, although in lower yields. A rational interpretation of this SN2-ET dichotomy is given on the basis of the full distribution of products observed when 5-hexenyl fluoride and 1,1-dimethyl-5-hexenyl fluoride were are used as radical probes in their reaction with Li2C12H10 and LiC12H10. 相似文献
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Tsunehisa Hirashita Yousuke Hayashi Kazuma Mitsui Shuki Araki 《Tetrahedron letters》2004,45(16):3225-3228
Vinyl and methylindium ate complexes (indates) were prepared and both the tendency of immigration and regioselectivity toward cinnamyl bromide were investigated. The vinyl group was more preferably transferred than the Me group, giving a regioisomeric mixture of SN2 and SN2′ products. The ratio of SN2/SN2′ selectivity can be controlled by solvents; in the presence of polar solvents, such as N-butylpyrrolidone (NBP) and THF, the SN2′ product was mainly obtained, whereas the SN2 product was selectively prepared in solutions containing hexane. The vinylindium compound, generated by the reaction of allylic-type diindium reagents with imine, was also converted to the corresponding vinyl indate, which was allowed to react with allyl chloride to give a three-component coupling product. 相似文献
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Martta Asikainen 《Tetrahedron letters》2010,51(49):6454-6456
Reaction of cuprates derived from R3MgBr/CuI/LiBr (R3 = n-alkyl) with R1CCCH(O2CR2)2 (R1 = sp2 hybridised substituent, R2 = mainly Me, alkyl, Ph) provides access to allenyl esters R1R3CCCH(O2CR2) (51-88%). Such species are not accessible via rearrangement of precursor propargylic R1R3C(O2CR2)CCH. 相似文献
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Phenyl telluride anion was prepared in liquid ammonia by reaction of dipheyyl ditelluride with two equivalents of sodium metal under nitrogen. This anion reacts with haloarenes under irradiation to form aryl phenyl tellurides, probably by the photo-SRN1 mechanism of aromatic substitution. 相似文献
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Jonathan T. Reeves Daniel R. Fandrick Zhulin Tan Jinhua J. Song Nathan K. Yee Chris H. Senanayake 《Tetrahedron letters》2009,50(25):3077-5222
Several diethyl 2-cumylmalonates underwent fragmentation and dimerization in PPA at elevated temperatures to give 1,1,3-trimethyl-3-arylindanes in good yields. The same products were obtained from 2-cumylmalonic acid, ethyl 2-cumylcyanoacetate, and 2-cumyl Meldrum’s acid. This represents the first example of an SN1/E1 ionization with diethyl malonate as the leaving group. 相似文献
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A convergent enantioselective synthesis of panclicin-D has been reported from simple octanal using syn aldol reaction via intramolecular SN2 displacement reaction for the first time towards the construction of anti-β-lactones in panclicin-D. The key steps involved are C-allylation, asymmetric aldolization under Crimmins condition, intramolecular SN2 displacement, and Mitsunobu esterification reaction. 相似文献
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Dilithium naphthalene (Li2C10H8) displays a SN2 reactivity profile in its reaction with alkyl fluorides (n-, s- and t-octyl fluoride). SN2 seems to be the dominant mechanism operating with primary alkyl fluorides, which presumably turns into competition with ET as we move to secondary and tertiary alkyl fluorides. Significantly, lithium naphthalene (LiC10H8) seems to have also an important nucleophilic component when reacting with alkyl fluorides, in contrast to the previously proposed general ET process valid for all alkyl halides. These results explain the observed distribution of products and are reinforced by a complete analysis of the products originated by the reaction with 6-halohexenyl radical probes, whose main alkylation products are described here for the first time. 相似文献
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Márcio S. Silva 《Tetrahedron letters》2009,50(47):6498-6501
Lithium and magnesium organotellurolates were reacted with lactones producing the corresponding tellurocarboxylic acids. Treatment of the reaction mixture with lithium aluminum hydride allowed the isolation of the corresponding hydroxytellurides in a one-pot operation. 相似文献
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Neutron scattering and computer simulation techniques have been used to investigate the defect cluster structure of CaF2 doped with 5% La3?. The results strongly support the formation of small discrete clusters rather than the superstructures that have been suggested in recent studies of anion excess fluorites. The type of cluster that emerges as dominant comprises an interstitial-dopant dimer (of the 2:2:2 type) which has captured an additional F? interstitial. The formation of such clusters is supported by recent ITC studies. 相似文献
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The chemoselective SN2′ reaction of a variety of primary nitroalkanes to dialkyl 2-(bromomethyl)fumarates can be efficiently performed under cetyltrimethylammonium hydroxide (CTAOH) catalysis. The α,β-unsaturated esters were obtained in satisfactory to good yields with the complete retention of the nitro group. 相似文献
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The voltammogram of aryldiazonium tetrafluoroborates in acetonitrile (ACN), at low concentration, shows a first one-electron wave followed at a more negative potential by a small second wave; this last one corresponds to the reduction of the radical formed at the level of the first wave. Simulation of the voltammogram permits one to determine the standard redox potential of the radical/anion couple Eo(Ph./Ph-) = 0.05 V/SCE and the reduction mechanism of the diazonium cation. An electron transfer concerted with the cleavage of the C-N bond furnishes the aryl radical; this radical undergoes two competitive reactions: reduction at the electrode and H-atom transfer. 相似文献
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Application of the configuration mixing model to the SN2 reaction illustrates that charge development in an SN2 reaction is not linearly related to the position of the transition state along the reaction coordinate. 相似文献
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A stereoselective method for the synthesis of substituted tetrahydrofuran derivatives employing a tandem alkylation-Michael addition sequence to vinylogous carbonates is developed. The method could be used to synthesize THFs bearing tertiary ethers. Further, the method is extended to the synthesis of adjacent bis-THFs. 相似文献
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Roberto Fernández de la Pradilla Alma Viso Sonia Castro Jorge Fernández Pilar Manzano Mariola Tortosa 《Tetrahedron》2004,60(37):8171-8180
The SN2′ displacement of readily available vinyl epoxy sulfoxides with organocopper reagents takes place in good yields with high anti selectivity and a good degree of E/Z stereocontrol to produce enantiopure α-hydroxy vinyl sulfoxides. A second allylic displacement on the related mesyloxy vinyl sulfoxides allows for the asymmetric construction of two adjacent chiral centers. In addition, cuprate mediated SN2′ addition to alkynyl epoxy sulfoxides affords α-hydroxy allenyl sulfoxides in good yields. 相似文献