The Catalytic Asymmetric Intermolecular Prins Reaction

Despite their significant potential, catalytic asymmetric reactions of olefins with formaldehyde are rare and metal-free approaches have not been previously disclosed. Here we describe an enantioselective intermolecular Prins reaction of styrenes and paraformaldehyde to form 1,3-dioxanes, using confined imino-imidodiphosphate (iIDP) Brønsted acid catalysts. Isotope labeling experiments and computations suggest a concerted, highly asynchronous addition of an acid-activated formaldehyde oligomer to the olefin. The enantioenriched 1,3-dioxanes can be transformed into the corresponding optically active 1,3-diols, which are valuable synthetic building blocks

Catalytic Asymmetric Spirocyclizing Diels–Alder Reactions of Enones: Stereoselective Total and Formal Syntheses of α-Chamigrene, β-Chamigrene, Laurencenone C, Colletoic Acid, and Omphalic Acid

We disclose a general catalytic enantioselective Diels–Alder reaction of exo-enones with dienes to give spirocyclanes. The obtained products feature highly congested quaternary stereogenic spirocenters and are used in concise total and formal syntheses of several sesquiterpenes, including of α-chamigrene, β-chamigrene, laurencenone C, colletoic acid, and omphalic acid. The stereo- and regioselectivities of our spirocyclizing cycloaddition are effectively controlled by strongly acidic and confined imidodiphosphorimidate catalysts. Computational studies shed light on the origin of reactivity and selectivity

Catalytic Asymmetric Hydroalkoxylation of C–C Multiple Bonds

Asymmetric hydroalkoxylation of alkenes constitutes a redox-neutral and 100% atom-economical strategy toward enantioenriched oxygenated building blocks from readily available starting materials. Despite their great potential, catalytic enantioselective additions of alcohols across a C–C multiple bond are particularly underdeveloped, especially compared to other hydrofunctionalization methods such as hydroamination. However, driven by some recent innovations, e.g., asymmetric MHAT methods, asymmetric photocatalytic methods, and the development of extremely strong chiral Brønsted acids, there has been a gratifying surge of reports in this burgeoning field. The goal of this review is to survey the growing landscape of asymmetric hydroalkoxylation by highlighting exciting new advances, deconstructing mechanistic underpinnings, and drawing insight from related asymmetric hydroacyloxylation and hydration. A deep appreciation of the underlying principles informs an understanding of the various selectivity parameters and activation modes in the realm of asymmetric alkene hydrofunctionalization while simultaneously evoking the outstanding challenges to the field moving forward. Overall, we aim to lay a foundation for cross-fertilization among various catalytic fields and spur further innovation in asymmetric hydroalkoxylations of C–C multiple bonds

Nonequilibrium tricriticality in one dimension

We show the existence of a nonequilibrium tricritical point induced by a repulsive interaction in one dimensional asymmetric exclusion process. The tricritical point is associated with the particle-hole symmetry breaking introduced by the repulsion. The phase diagram and the crossover in the neighbourhood of the tricritical point for the shock formation at one of the boundaries are determined.Comment: 6 pages; 4 figure

Homologation of the Fischer Indolization: A Quinoline Synthesis via Homo‐Diaza‐Cope Rearrangement

We disclose a new Brønsted acid promoted quinoline synthesis, proceeding via homo‐diaza‐Cope rearrangement of N‐aryl‐N′‐cyclopropyl hydrazines. Our strategy can be considered a homologation of Fischer's classical indole synthesis and delivers 6‐membered N‐heterocycles, including previously inaccessible pyridine derivatives. This approach can also be used as a pyridannulation methodology toward constructing polycyclic polyheteroaromatics. A computational analysis has been employed to probe plausible activation modes and to interrogate the role of the catalyst

Catalytic Asymmetric Synthesis of Unprotected β²-Amino Acids

We report here a scalable, catalytic one-pot approach to enantiopure and unmodified β2-amino acids. A newly developed confined imidodiphosphorimidate (IDPi) catalyzes a broadly applicable reaction of diverse bis-silyl ketene acetals with a silylated aminomethyl ether, followed by hydrolytic workup, to give free β2-amino acids in high yields, purity, and enantioselectivity. Importantly, both aromatic and aliphatic β2-amino acids can be obtained using this method. Mechanistic studies are consistent with the aminomethylation to proceed via silylium-based asymmetric counteranion-directed catalysis (Si-ACDC) and a transition state to explain the enantioselectivity is suggested on the basis of density functional theory calculation

Tunnelling Induced ground settlement considering soil variability

Ground settlement need to be predicted well so that necessary precautionary measures could be adopted. Ground deformation behavior due to tunnel construction in inhomogeneous soil has been studied in the past few decades by many researchers. When tunnel-induced ground, settlement is predicted by considering average soil properties, it is likely to miss the true settlement characteristics and failure mechanism due to the inherent heterogeneity of the ground. In this paper, spatial variability of the ground is considered in the numerical analysis to simulate the ground settlement. A numerical model is developed using the Finite-Difference based numerical code FLAC3D to simulate tunnel construction with earth pressure balance (EPB) TBMs for a case study. Both 2D and 3D random fields are simulated in the numerical model. Results are systematically compared with some of the empirical and analytical methods for predicting ground settlement. Spatial distribution is found to have a significant effect on surface settlements and overall ground behavior

Experimental observations and statistical modeling of crack propagation dynamics in limestone by acoustic emission analysis during freezing and thawing

The timing and location of microcracking events, their propagation and coalescence to form macrocracks, and their development by tension, shearing or mixed modes are little known but essential to understanding the fracture of intact rock by freezing and thawing. The aims of the present study are to investigate the mechanisms and transition of microcracking and macrocracking during repeated freeze-thaw, and to develop a statistical model of crack propagation that assesses the distance and angular relationship of neighboring cracking events arranged in their temporal order of occurrence. Eight acoustic emission (AE) sensors mounted on a 300 mm cubic block of chalk captured the three-dimensional locations of microcracking events in their temporal order of occurrence during 16 seasonal freeze-thaw cycles simulating an active layer above permafrost. AE events occurred mostly during thawing periods (45%) and freeze-to-thaw transitions (37%) rather than during freezing periods (9%) and thaw-to-freeze transitions (8%), suggesting that most AE (microcrack) events were driven by the process of ice segregation rather than volumetric expansion. The outcomes of a novel statistical model of crack propagation based on two boundary conditions—inside-out and outside-in modes of cracking—were assessed based on Bayes’ theorem by testing the hypothesis that the inside-out mode of cracking was favored by tensional activity, whereas the outside-in mode was supported by shearing events. In both situations, the hypothesis accounted for 54%–73% confidence level. The microcrack propagation model can distinguish reasonably between cracks formed by volumetric expansion and ice segregation