Cobalt(I)-catalyzed [6+2] cycloadditions of cyclooctatetra(tri)ene with alkynes

The cobalt-catalyzed [6+2] cycloaddition of cyclooctatetraene 1 with alkynes 3 affords monosubstituted bicyclo[4.2.2]deca-2,4,7,9-tetraenes 4 in fair to good yields. Due to the valence tautomerism, 1,3,5-cyclooctatriene 2, in equilibrium with bicyclo[4.2.0]octa-2,4-diene A, and alkynes 3 are converted to 10 and 11 according to [6+2] and [4+2] cycloadditions, respectively.     

Rhodium-catalyzed stereoselective formation of Z-enamines from allylaziridines

Rhodium (I)-catalyzed isomerization of N-allylaziridines affords isolable Z-enamines in excellent yields and with high stereoselectivity. Cationic [Rh(BINAP)(COD)]OTf and RhH(CO)(PPh3)3 follow the same selectivity toward the Z-isomers. This selectivity is not observed with other N-allylamines which give the thermodynamically more stable E-isomers. These unexpected results suggest a possible deviation from the commonly accepted mechanism of isomerization. Preliminary results show that the Z-enamines undergo cycloaddition with DMAD to form highly strained N-cyclobutenyl aziridines.     

C-Silylation de composes a fonction nitrile. Synthese de nitriles α-silicies

The direct silylation by Me₃SiCl/Li/THF of saturated nitriles having a hydrogen atom in the α position with respect to the function leads, according to a simple and rapid process, to the corresponding α-silylated nitriles in yields that are moderate but much higher than those given by the comparable previously known routes. α, β-Unsaturated nitriles give the derivatives resulting from the disilylation of the double bond. Allyl or benzyl cyanide and diphenyl acetonitrile first undergo the elimination of the nitrile group (which behaves as a halogen atom) whereas cyanamid affords bis(trimethylsilyl)carbodiimide giving after further silylation the unexpected tris(trimethylsilyl)amine.     

Copper(I)-promoted palladium-catalyzed cross-coupling of unsaturated tri-n-butylstannane with heteroaromatic thioether

[reaction: see text] Palladium-catalyzed cross-coupling of vinyl- and arylstannanes with pi-electron-deficient heteroaromatics was performed in good yields. This Stille-type reaction was carried out with a methylthioether function as an electrophile in the presence of a copper(I) bromide-dimethyl sulfide complex.     

Diverse chirped optical solitons and new complex traveling waves in nonlinear optical fibers

This paper studies chirped optical solitons in nonlinear optical fibers. However, we obtain diverse soliton solutions and new chirped bright and dark solitons, trigonometric function solutions and rational solutions by adopting two formal integration methods. The obtained results take into account the different conditions set on the parameters of the nonlinear ordinary differential equation of the new extended direct algebraic equation method. These results are more general compared to Hadi et al(2018 Optik 172 545–53) and Yakada et al(2019 Optik197 163108).     

Broad band acousto-optic deflector for holographic memories

A practical inexpensive mechanism for effecting improved Rayleigh resolution in a random access deflector without sacrificing its performance has been constructed. It comprises an acousto-optic deflector in the form of a flat transducer grating, made from a single piezoelectric platelet. The deflector steers the acoustic column to track the Bragg angle as the acoustic frequency changes.     

New standing solitary waves in water

By means of the parametric excitation of water waves in a Hele-Shaw cell, we report the existence of two new types of highly localized, standing surface waves of large amplitude. They are, respectively, of odd and even symmetry. Both standing waves oscillate subharmonically with the forcing frequency. The two-dimensional even pattern presents a certain similarity in the shape with the 3D axisymmetric oscillon originally recognized at the surface of a vertically vibrated layer of brass beads. The stable, 2D odd standing wave has never been observed before in any media.     

Cyclobutene Formation in PtCl2‐Catalyzed Cycloisomerizations of Heteroatom‐Tethered 1,6‐Enynes

Aza(oxa)bicyclo[3.2.0]heptenes are accessed through the PtCl₂‐catalyzed cycloisomerizations of heteroatom‐tethered 1,6‐enynes featuring a terminal alkyne and amide as the solvent. It is shown that the weak coordinating properties of the solvent and alkyl substituent(s) at the propargylic carbon atom favor the formation of cyclobutenes instead of other possible cycloisomerization products such as 1,3‐diene derivatives or cyclopropane‐fused heterocycles.