Experimental and computational studies into an ATPH-promoted exo -Selective IMDA reaction: A short total synthesis of Δ 9 -THC

(Figure Presented) Reversal of fortune: The inherent cis stereoselectivity of an intramolecular Diels-Alder reaction is reversed through promotion with aluminum tris(2,6-diphenylphenoxide) (ATPH), allowing a total synthesis of the natural product Δ 9-te

The simplest Diels-Alder reactions are not: Endo -selective

There is a widespread perception that the high level of endo selectivity witnessed in many Diels-Alder reactions is an intrinsic feature of the transformation. In contrast to expectations based upon this existing belief, the first experimental Diels-Alder reactions of a novel, deuterium-labeled 1,3-butadiene with commonly used mono-substituted alkenic dienophiles (acrolein, methyl vinyl ketone, acrylic acid, methyl acrylate, acrylamide and acrylonitrile) reveal kinetic endo:exo ratios close to 1:1. Maleonitrile, butenolide, α-methylene γ-butyrolactone, and N-methylmaleimide behave differently, as does methyl vinyl ketone under Lewis acid catalysis. CBS-QB3 calculations incorporating solvent and temperature parameters give endo:exo product ratios that are in near quantitative agreement with these and earlier experimental findings. This work challenges the preconception of innate endo-selectivity by providing the first experimental evidence that the simplest Diels-Alder reactions are not endo-selective. Trends in behaviour are traced to steric and electronic effects in Diels-Alder transition structures, giving new insights into these fundamental processes.This work was supported by the Australian Research Council (DP160104322). MNP-R acknowledges that the computational component of this research was undertaken with the assistance of resources provided at the NCI National Facility through the National Computational Merit Allocation Scheme supported by the Australian Government

Triplet energy management between two signaling units through cooperative rigid scaffolds

[EN] Through-bond triplet exciplex formation in donor-acceptor systems linked through a rigid bile acid scaffold has been demonstrated on the basis of kinetic evidence upon population of the triplet acceptors (naphthalene, or biphenyl) by through-bond triplet-triplet energy transfer from benzophenone.Financial support from the Spanish Government (Grants SEV-2012-0267, CTQ2012-38754-C03-03, CTQ2013-47872-C2-1-P and JCI-2011-09926), EU (PCIG12GA-2012-334257), Generalitat Valenciana (Prometeo Program), and Technical University of Valencia (VLC/Campus, ASIC-UPV for computational facilities and Predoctoral FPI fellowship for P. Miro) is gratefully acknowledged.Miró Richart, P.; Vayá Pérez, I.; Sastre Navarro, GI.; Jiménez Molero, MC.; Marín García, ML.; Miranda Alonso, MÁ. (2016). Triplet energy management between two signaling units through cooperative rigid scaffolds. Chemical Communications. 52(4):713-716. https://doi.org/10.1039/c5cc08102eS71371652

Total Synthesis of a Dimeric Thymol Derivative Isolated from Arnica sachalinensis

The total synthesis of a dimeric thymol derivative (thymarnicol) isolated from Arnica sachalinensis was accomplished in 6 steps. A key biomimetic Diels–Alder dimerization was found to occur at ambient temperature and the final oxidative cyclization occurs when the substrate is exposed to air and visible light. These results indicate that this natural product is likely the result of spontaneous (non‐enzyme‐mediated) reactivity

A highly rigid and gas selective methanopentacene-based polymer of intrinsic microporosity derived from Tröger's base polymerization

Polymers of intrinsic microporosity (PIMs) have been identified as potential next generation membranematerials for the separation of gas mixtures of industrial and environmental relevance. Based on theexceptionally rigid methanopentacene (MP) structural unit, a Polymer of Intrinsic Microporosity (PIM-MPTB)was designed to demonstrate high selectivity for gas separations. PIM-MP-TB was prepared usinga polymerisation reaction involving the formation of Troger's base linking groups and demonstrated an ¨apparent BET surface area of 743 m2 g1 as a powder. The microporosity of PIM-MP-TB was alsocharacterized by chain packing simulations. PIM-MP-TB proved soluble in chlorinated solvents and wascast as a robust, free-standing film suitable for gas permeation measurements. Despite lower gaspermeability as compared to previously reported PIMs, high selectivities for industrially relevant gas pairswere obtained, surpassing the 2008 Robeson upper bound for H2/CH4 and O2/N2, (e.g., PO2 ¼ 999Barrer; aO2/N2 ¼ 5.0) and demonstrating a clear link between polymer rigidity and selectivity. Upon aging,the permeability data move parallel to the Robeson upper bounds with a decrease of permeability,compensated by a related increase in selectivity. Mixed gas permeation measurement for CO2/CH4 andCO2/N2 mixtures confirmed the excellent selectivity of PIM-MP-TB for potentially relevant separationssuch as biogas upgrading and CO2 capture from flue gas. Importantly, unlike other high performingPIMs, PIM-MP-TB is prepared in four simple steps from a cheap starting materi