Grob fragmentation of 2-azabicyclo[2.2.2]oct-7-ene: tool for the stereoselective synthesis of polysubstituted piperidines

The Grob fragmentation of azabicyclo[2.2.2]octene leads to a dihydropyridinium intermediate. This highly reactive species reacts with a variety of organocuprates and other soft nucleophiles in a regioselective manner, allowing for the rapid and stereoselective synthesis of 2,3,4-trisubstituted 1,2,3,4-tetrahydropyridines. The resulting products were either reduced in situ to the corresponding piperidine or used to achieve the stereoselective construction of various nitrogen heterocycles.     

Suzuki coupling of potassium cyclopropyl- and alkoxymethyltrifluoroborates with benzyl chlorides

Efficient Csp(3)-Csp(3) Suzuki couplings have been developed with both potassium cyclopropyl- and alkoxymethyltrifluoroborates. Moderate to good yields have been achieved in the cross-coupling of potassium cyclopropyltrifluoroborate with benzyl chlorides possessing electron-donating or electron-withdrawing substituents. Benzyl chloride was also successfully cross-coupled to potassium alkoxymethyltrifluoroborates derived from primary, secondary, and tertiary alcohols.     

Closed time-like curves in flat Lorentz space–times

We consider the region of closed time-like curves (CTCs) in three-dimensional flat Lorentz space–times. The interest in this global geometrical feature goes beyond the purely mathematical one. Such space–times are lower-dimensional toy models of sourceless Einstein gravity or cosmology. In three dimensions all such space–times are known: they are quotients of Minkowski space by a suitable group of Poincaré isometries. The presence of CTCs would indicate the possibility of “time machines”, a region of space–time where an object can travel along in time and revisit the same event. Such space–times also provide a testbed for the chronology protection conjecture, which suggests that quantum back reaction would eliminate CTCs. In particular, our interest in this note will be to find the set free of CTCs for , where is modeled on Minkowski space and γ is a Poincaré transformation. We describe the set free of CTCs where γ is hyperbolic, parabolic, and elliptic.     

The affine deformation space of a rank two Schottky group: a picture gallery

The Margulis invariant of an affine hyperbolic element measures the signed Lorentzian displacement along the unique closed geodesic in its class. Given a group of affine transformations of Minkowski spacetime whose linear part is Schottky, the Margulis invariant is a useful tool in determining properness of its action. This paper, based on a presentation given at CGG IV Oostende 2005, describes the affine deformation space of a rank two Schottky group. Several illustrations are included, contrasting the difference between the case of a three-holed sphere and that of a one-holed torus. Paper based on a presentation given at CGG IV Oostende 2005. Attendance of the conference and the subsequent writing of this paper was made possible by an NSERC Discovery Grant.     

Borocyclopropanation of Styrenes Mediated by UV‐light Under Continuous Flow Conditions

Herein, we report a user‐friendly and metal‐free UV‐A light mediated borocyclopropanation of styrenes using continuous flow technology. A broad range of styrene derivatives can be cyclopropanated in good yields within 1 h residence time to produce highly valuable cyclopropylboronate esters with modest to good diastereoselectivities. The reaction is also applicable to α‐substituted styrenes. Mechanistic studies support a photoredox process during which xanthone, a well‐known organic photosensitizer, can easily reach a photoexcited state that is available for both an oxidative and a reductive quenching.     

Asymmetric, catalytic synthesis of alpha-chiral amines using a novel bis(phosphine) monoxide chiral ligand

We have shown that Me-DuPHOS monoxide (BozPHOS) is a very effective ligand in the copper-catalyzed addition of dialkylzinc to N-phosphinoylimines providing access to alpha-chiral amines. The new ligand is particularly effective for the addition of the lesser reactive dimethylzinc. The major advantages of this process are high yields, broad substrate scope, and high enantioselectivities with low catalyst loading (3 mol %).     

Thermal-, pressure-, and light-induced spin transition in novel cyanide-bridged FeII-AgI bimetallic compounds with three-dimensional interpenetrating double structures (FeIILx[Ag(CN)2]2).G

Low-spin, high-spin and spin-transition behaviours have been observed for the doubly interpenetrating three-dimensional bimetallic compounds (FeII(pz)[Ag(CN)2]2).pz (pz = pyrazine), (FeII(4,4'-bipy)2[Ag(CN)2]2) (4,4'-bipy = 4,4'-bipyridine), and (FeII(bpe)2[Ag(CN)2]2) (bpe = bispyridylethylene), respectively. The single crystals of the bpe derivative undergo a spin transition with a large hysteresis loop at about 95 K. After several warming and cooling cycles, the single crystals become a microcrystalline powder with 50% spin transition. Influence of pressure--as well as light-induced excited spin-state trapping (LIESST) on the thermal 50% spin transition of the microcrystalline sample has also been investigated. Thermal spin-transition behaviour has also been induced at pressures higher than 1 bar for the 4,4'-bipy derivative. Both the 4,4'-bipy and bpe derivatives show strong pressure dependence of the spin state at 300 K.     

Mild method for the conversion of amides to thioamides

Aqueous ammonium sulfide was found to be an ideal substitute for hydrogen sulfide for the thiolysis of activated amides. High yields of the corresponding thioamides were obtained for a broad range of substrates, using two different procedures that are both operationally simple and inexpensive, as well as amenable to large-scale preparation. Preliminary results indicate that aqueous ammonium sulfide may also replace hydrogen sulfide in the synthesis of thionoesters from amides.     

Theoretical study of 31P, 31P coupling constants in cyclotriphosphazenes

Several scalar coupling constants (mainly 31P, 31P) were calculated for 10 cyclotriphosphazenes and compared with experimental results when available. Although the experimental values cannot be reproduced, the calculated values are proportional to the experimental values. Some difficult cases, such as 19F, 19F couplings, are discussed.