Beyond Reppe: Building Substituted Arenes by [2+2+2] Cycloadditions of Alkynes

Synthetic sequel : The transition‐metal‐catalyzed [2+2+2] cycloaddition is an established method for the construction of carbocyclic frameworks but is often plagued by poor selectivity. Recent literature paints a promising picture—a more general metal‐catalyzed [2+2+2] cycloaddition can be accomplished intermolecularly using three separate alkynes to furnish highly substituted arenas (see scheme).

     

Total Synthesis of Indolizidine Alkaloid (−)‐209D: Overriding Substrate Bias in the Asymmetric Rhodium‐Catalyzed [2+2+2] Cycloaddition

CO! You had me at hello : The use of chiral biphenyl‐based phosphoramidite ligands on rhodium provides an efficient [2+2+2] cycloaddition between terminal alkyl alkynes and alkenyl isocyanates (see scheme). The cycloaddition proceeds through a CO migration pathway, and facilitates a rapid four‐step asymmetric synthesis of indolizidine (?)‐209D.

     

Complex and chaotic oscillations in a model for the catalytic hydrogen peroxide decomposition under open reactor conditions

Numerous periodic and aperiodic dynamic states obtained in a model for hydrogen peroxide decomposition in the presence of iodate and hydrogen ions (the Bray-Liebhafsky reaction) realized in an open reactor (CSTR), where the flow rate was the control parameter, have been investigated numerically. Between two Hopf bifurcation points, different simple and complex oscillations and different routes to chaos were observed. In the region of the mixed-mode evolution of the system, the transitions between two successive mixed-mode simple states are realized by period-doubling of the initial state leading to a chaotic window in which the next dynamic state emerges mixed with the initial one. It appears in increasing proportions in concatenated patterns until total domination. Thus, with increasing flow rate the period-doubling route to chaos was obtained, whereas with decreasing flow rate the peak-adding route to chaos was obtained. Moreover, in very narrow regions of flow rates, chaotic mixtures of mixed-mode patterns were observed. This evolution of patterns repeats until the end of the mixed-mode region at high flow rates that corresponds to chaotic mixtures of one large and many small amplitude oscillations. Starting from the reverse Hopf bifurcation point and decreasing the flow rate, simple small amplitude sinusoidal oscillations were encountered and then the period-doubling route to chaos. With a further decreasing flow rate, the mixed-mode oscillations emerge inside the chaotic window.     

Synthesis, characterization, and the role of counterion in stabilizing trigonal pyramidal copper(I)/2,2′bipyridine complexes containing electron-poor methyl acrylate

Copper(I)/2,2′-bipyridine complexes, [Cu^I(bpy)(π-CH₂CHCOOCH₃)][A] have been synthesized and characterized. These complexes are used in copper(I) mediated cyclopropanation and aziridination reactions of methyl acrylate and represent the first class of trigonal pyramidal copper(I) complexes with π-coordinated electron poor olefins. In the case of 1 and 3, weak coordination of the counterion was observed. The counterion was noncoordinating in complex 2, which was dimeric in the solid state with the oxygen atoms of the carbonyl moieties in methyl acrylate bridging two copper(I) centers.     

Exploring cocrystal-cocrystal reactivity via liquid-assisted grinding: the assembling of racemic and dismantling of enantiomeric cocrystals

The reaction between pairs of enantiomeric cocrystals involving caffeine or theophylline and a chiral cocrystal former has been investigated by liquid-assisted grinding: we demonstrate two different outcomes for such cocrystal-cocrystal reactions.     

Rhodium-catalyzed [2 + 2 + 2] cycloaddition of alkenyl isocyanates and alkynes

A rhodium(I)-catalyzed [2 + 2 + 2] cycloaddition between alkenyl isocyanates and alkynes has been developed. Heating a mixture of an alkenyl isocyanate and a symmetrical internal alkyne in the presence of [Rh(ethylene)2Cl]2/P(4-OMe-C6H4)3 in toluene delivers substituted indolizinones and quinolizinones. Depending on the substrates, a rare fragmentation of the isocyanate unit can be involved within the cycloaddition process to furnish a vinylogous amide embedded in the indolizinone.     

Evaluation of decay times in coupled spaces: an efficient search algorithm within the Bayesian framework

This paper discusses an efficient method for evaluating multiple decay times within the Bayesian framework. Previous works [N. Xiang and P. M. Goggans, J. Acoust. Soc. Am. 110, 1415-1424 (2001); 113, 2685-2697 (2003); N. Xiang, P. M. Goggans, T. Jasa, and M. Kleiner, 117, 3707-3715 (2005)] have applied the Bayesian inference to cope with demanding tasks in estimating multiple decay times from Schroeder decay functions measured or calculated in acoustically coupled spaces. Since then a number of recent works call for efficient estimation methods within the Bayesian framework. An efficient analysis is of practical significance for better understanding and modeling the sound energy decay process in acoustically coupled spaces or even in single spaces for reverberation time estimation. This paper will first formulate the Bayesian posterior probability distribution function (PPDF) in a matrix form to reduce the dimensionality as applied to the decay time evaluation. Based on existence of only global extremes of PPDFs as observed from extensive experimental data, this paper describes a dedicated search algorithm for an efficient estimation of decay times.     

Four-Dimensional Geometric Quantities versus the Usual Three-Dimensional Quantities: The Resolution of Jackson’s Paradox

In this paper we present definitions of different four-dimensional (4D) geometric quantities (Clifford multivectors). New decompositions of the torque N and the angular momentum M (bivectors) into 1-vectors N_s, N_t and M_s, M_t, respectively, are given. The torques N_s, N_t (the angular momentums M_s, M_t), taken together, contain the same physical information as the bivector N (the bivector M). The usual approaches that deal with the 3D quantities etc. and their transformations are objected from the viewpoint of the invariant special relativity (ISR). In the ISR, it is considered that 4D geometric quantities are well-defined both theoretically and experimentally in the 4D spacetime. This is not the case with the usual 3D quantities. It is shown that there is no apparent electrodynamic paradox with the torque, and that the principle of relativity is naturally satisfied, when the 4D geometric quantities are used instead of the 3D quantities.