Mild generation of 5-(2'-deoxyuridinyl)methyl radical from a phenyl selenide precursor

[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.     

The reaction of biphenyl radical anion and dianion with alkyl fluorides. From ET to SN2 reaction pathways and synthetic applications

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 (S_N2) and the electron transfer (ET), can compete to yield the same alkylation products in what is known as the S_N2-ET dichotomy. S_N2 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 S_N2-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.     

Reaction of indium ate complexes with allylic compounds. Controlling SN2/SN2′ selectivity by solvents

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 S_N2 and S_N2′ products. The ratio of S_N2/S_N2′ selectivity can be controlled by solvents; in the presence of polar solvents, such as N-butylpyrrolidone (NBP) and THF, the S_N2′ product was mainly obtained, whereas the S_N2 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.     

An SN2′ displacement approach to allenyl acetates

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.     

Photo-SRN1 reactions of phenyl telluride anion with haloarenes

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-S_RN1 mechanism of aromatic substitution.     

Acid-promoted SN1/E1 fragmentation/dimerization of 2-cumylmalonates

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 S_N1/E1 ionization with diethyl malonate as the leaving group.     

Convergent synthesis of panclicin-D via intramolecular SN2 displacement approach

A convergent enantioselective synthesis of panclicin-D has been reported from simple octanal using syn aldol reaction via intramolecular S_N2 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 S_N2 displacement, and Mitsunobu esterification reaction.     

On the dichotomy of the SN2/ET reaction pathways: an apparent SN2 reactivity in the reaction of naphthalene dianion with alkyl fluorides

Dilithium naphthalene (Li₂C₁₀H₈) displays a S_N2 reactivity profile in its reaction with alkyl fluorides (n-, s- and t-octyl fluoride). S_N2 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.     

The soft nucleophilicity of organotellurolates driving the SN2-type lactone ring-opening reaction

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.     

The defect structure of anion excess CaF2

Neutron scattering and computer simulation techniques have been used to investigate the defect cluster structure of CaF₂ doped with 5% La^3?. 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.     

Chemoselective SN2′ reaction of nitroalkanes to dialkyl 2-(bromomethyl)fumarates under cetyltrimethylammonium hydroxide (CTAOH) catalysis

The chemoselective S_N2′ 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.     

The standard redox potential of the phenyl radical/anion couple

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.     

Is charge development a measure of SN2 transition state structure?

Application of the configuration mixing model to the S_N2 reaction illustrates that charge development in an S_N2 reaction is not linearly related to the position of the transition state along the reaction coordinate.     

Tandem SN2-Michael addition to vinylogous carbonates for the stereoselective construction of 2,3,3,5-tetrasubstituted tetrahydrofurans

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.     

Sulfoxide-controlled SN2′ displacements between cuprates and vinyl and alkynyl epoxy sulfoxides

The S_N2′ 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 S_N2′ addition to alkynyl epoxy sulfoxides affords α-hydroxy allenyl sulfoxides in good yields.