Addition of dichlorocarbene to aporphinoids: a new route to homoaporphines

An easy and efficient method for the synthesis of homoaporphines is described. It is based on the ring C homologation of aporphines via dichlorocarbene adducts.     

Olefin addition to acetylated glycals. A new route to C-glycosides.

Olefins react with glycals in the presence of Lewis acids providing a new route to C-glycosides.     

Addition of malonyl radicals to glycals with C-1 acceptor groups: remarkable influence of the substituents on the product distribution

The ceric(IV) ammonium nitrate (CAN)-mediated radical addition of dimethyl malonate to glycals 1 affords methyl glycosides 2 and ortho esters 3 as main products; the product distribution strongly depends on the substitution pattern at the 1-position, which can be rationalized in terms of the oxidation potentials of the intermediary anomeric radicals.     

General method for synthesizing pyranoid glycals. A new route to allal and gulal derivatives

[reaction: see text] Pyranoid glycals of all configurations can be obtained from pentoses through an olefination-cyclization-elimination sequence. The elimination can be carried out with excellent yields under radical conditions or by using common reductive reagents such as Zn/Cu, TiCl(4)/LiAlH(4), or lithium naphthalenide. The proposed method is appropriate for the synthesis of glycals with allo or gulo configurations because the cyclization step is more efficient for these substrates.     

Intramolecular cyclization of beta-amino and beta-ammonio radicals: a new synthetic route to the 1-azabicyclo

Treatment of 1-(2-phenylselenoethyl)-1,2,5,6-tetrahydropyridine (15) with tributyltin hydride affords only the product of reduction, demonstrating the reluctance of the 5-hexenyl radical 9 to undergo ring closure. When the nature of the radical is modified, either by introduction of an ester group at C4 or via its quaternary ammonium salt, cyclization occurs readily; while the radical 52 gives an excellent yield of 1-methyl-1-azoniabicyclo[3.2.1.]octyl bromide (55) uncontaminated with the product of reduction, the bicyclic product from 21 is accompanied by some reduced material. Production of the unwanted alkene can be eliminated in the latter by recourse to the quaternary ammonium ester 1-(2-bromoethyl)-4-carbethoxy-1-methyl-1,2,5,6-tetrahydropyridinium bromide (35) which, when exposed to tributyltin hydride, affords a 1:1 endo/exo mixture of 4-carbethoxy-1-methyl-1-azoniabicyclo[3.2.1]octyl bromide (37) exclusively. These results support the demonstration of the powerful polar effect of an ester function when attached to the double bond of a 5-hexenyl system, a property which can be exploited in the case of the radical 58. Treatment of the precursor, 1-(2-bromoethyl)-3-carbethoxy-1-methyl-3-pyrrolinium bromide (60), with tributyltin hydride generates 58 which is found to cyclize with high regioselectivity, affording a convenient high-yielding synthesis of the endo/exo isomers of 3-carbethoxy-1-methyl-1-azoniabicyclo[2.2.1]heptyl bromide 57. The isomeric bicyclo[2.2.1]heptyl ester 63 was not detected. These observations are in accordance with predictions based upon frontier molecular orbital considerations.     

Addition of N-heterocyclic carbenes to a ruthenium(VI) nitrido polyoxometalate: a new route to cyclic guanidines

The scope of N-atom transfer from the electrophilic ruthenium(VI) nitrido containing polyoxometalate [PW(11)O(39)Ru(VI)N](4-) has been extended to the N-heterocyclic carbene {CH(2)(Mes)N}(2)C and the coupling product {CH(2)(Mes)N}(2)CNH(2)(+) characterized by (1)H NMR and high-resolution mass spectrometry. Because guanidines display many fields of applications ranging from biology to supramolecular chemistry, this could afford an original route to the synthesis of cyclic guanidines. This also enlarges the potential of nitrido complexes in the synthesis of heterocycles, mainly illustrated in the literature through the formation of aziridines through N-atom transfer to alkenes. In the course of the reaction, the ruthenium(III)-containing polyoxometallic intermediate [PW(11)O(39)Ru(III){NC{N(Mes)CH(2)}(2)}](5-) has been thoroughly characterized by continuous-wave and pulsed electron paramagnetic resonance, which nicely confirms the presence of the organic moiety on the polyoxometallic framework, Ru K-edge X-ray absorption near-edge structure, and electrochemistry.     

Addition of trichloromethyl radicals to tetrachloroethylene

The gamma-radiation-induced free-radical chain reactions in liquid CCl₄? C₂Cl₄? c? C₆H₁₂ mixtures were studied in the temperature range of 363–448°K. The main products in this system are chloroform, hexachloropropene and chlorocyclohexane. These products are formed via reactions (1)–(5): with G values (molec/100 eV) of the order of magnitude of 10² and 10³ at the lowest and highest temperatures, respectively. Values of k₂/k₁ were determined from the product distribution. In turn, these values gave the following Arrhenius expression for k₂/k₁ (θ = 2.303RT, in kcal/mol): From this result and the previously determined Arrhenius parameters of reaction (1), k₂ is found to be given by .     

Addition of methoxy radicals to olefins

The addition of methoxy radicals to several olefins has been studied by a competitive method at 127°C in gas phase. The thermal decomposition of dimethyl peroxide was used as methoxy radical source. The rate of addition to the double bond was measured relative to the oxidation of carbon monoxide. For the addition to ethylene it was obtained that This rate constant is similar to the one shown by methyl radicals under similar conditions. From the relative rate of addition to several chlorinated and fluorinated olefins it can be concluded that methoxy radicals show very little “electrophilic” character.     

Addition of sulfur radicals to fullerenes

The addition of oxygen‐centered radicals to fullerenes has been intensively studied due to their role in cell protection against against hydrogen peroxide induced oxidative damage. However, the analogous reaction of sulfur‐centered radicals has been largely overlooked. Herein, we investigate the addition of S‐centered radicals to C₅₀, C₆₀, C₇₀, and C₁₀₀ fullerenes by means of DFT calculations. The radicals assayed were: S, SH, SCH₃, SCH₂CH₃, SC₆H₅, SCH₂C₆H₅, and the open‐disulfide SCH₂CH₂CH₂CH₂S. Sulfur, the most reactive species, prefers to be attached to a 66‐bond of C₆₀ with a binding energy (E_bind) of 2.4 eV. For the SR radicals the electronic binding energies to C₆₀ are 0.77, 0.74, 0.58, 0.67, and 0.35 eV for SH, SCH₃, SCH₂CH₃, SCH₂C₆H₅, and SC₆H₅, respectively. The reactivity of C₆₀ toward SR radicals can be increased by lithium doping. For Li@C₆₀, the E_bind is increased by 0.65 eV with respect to C₆₀, but only by 0.33 eV for the exohedral doping. Fullerenes act like free radical sponges. Indeed, the C₆₀‐SR E_bind can be duplicated if two radicals are added in ortho or para positions. The enhanced reactivity because of multiple additions is mostly a local effect, although the addition of one radical makes the whole cage more reactive. Therefore, as observed for hydroxylated fullerenes, they should protect cells from oxidative damage. However, the thiolated fullerenes have one advantage, they can be easily attached to gold nanoparticles. For the addition on pentagon junctions smaller fullerenes like C₅₀ are more reactive than C₆₀. Interestingly, C₇₀ is as reactive as C₆₀, even for the addition on the equatorial belt. For larger fullerenes like C₁₀₀, reactivity decreases for the carbon atoms belonging to hexagon junctions. © 2010 Wiley Periodicals, Inc. Int J Quantum Chem, 2010     

A new route to 2-styrylbenzimidazoles

An attempt was made to prepare 2-benzylquinoxalin-3-one by hydrolyzing the azlactone, 2-phenyl-4-benzylidene-5-oxazolone to β-phenylpyruvic acid and then treating this in situ with o-phenylenediamine (OPDA). The initial hydrolysis apparantly proceeded only as far as opening the azlactone ring forming 2-benzamidocinnamic acid which condensed with OPDA to form a substituted styrylbenzimidazole.     

Rhodium-catalyzed carbonylation of 2-alkynylbenzylamine: a new route to the synthesis of benzazepinones

Rhodium-catalyzed carbonylation of 2-alkynylbenzylamines under water-gas shift reaction conditions gives a seven-membered heterocyclic product, 2,4-disubstituted-1,4-dihydrobenz[c]azepin-3-ones, in a good yield.     

Iodine catalyzed one-pot diamination of glycals with chloramine-T: a new approach to 2-amino-beta-glycosylamines for applications in N-glycopeptide synthesis

Iodine catalyzes a facile one-pot direct diamination of glycals with chloramine-T to afford stereoselectively 2-amino-beta-glycosylamine derivatives that serve as convenient precursors for the synthesis of N-linked glycopeptides.     

Addition of methyl radicals to carbon monoxide: Chemically and thermally activated decomposition of acetyl radicals

Chemically activated acetyl radicals, with an excitation energy of 78 kJ/mole, were formed by the addition of methyl radicals to carbon monoxide. At 273·K the pressure required to stabilize one half of the excited radicals was 500 torr. From measurements of the acetyl radical yield at pressures in the range of 700–2100 torr, and at temperatures in the range of 260–413 K, extrapolations to infinite pressure yielded kinetic parameters for the addition of methyl radicals to carbon monoxide, and for the thermal decomposition of acetyl radicals. The rate constants were found to be log k[cm³ / (mole·s)] = 11.2–25(kJ/mole/2.3) RT, and log k(s^?1) = 13.5?72 (kJ/mole)/2.3RT, respectively. Estimated thermochemical properties of the acetyl radical are ΔH_fº = ?17 kJ/mole and Sº = 262 J/K°mole.     

Synthesis of alpha-CF2-mannosides and their conversion to fluorinated pseudoglycopeptides

A methodology allowing the synthesis alpha-CF(2)-mannosides, based on the addition of a difluoroenoxysilane to a glycal followed by a dihydroxylation reaction, is described. The resulting 2,2-difluoro-2-mannosylacetate is converted into two pseudoglycopeptides which may act as E- and P-selectin inhibitors.