Krausekryger2071

A new non-natural β-amino acid, named 3-Ar-β-Morph, was designed and synthesized via a regio- and diastereoselective Pd-catalyzed C(sp3)H-arylation of the corresponding 2S,6S-(6-methoxymorpholin-2-yl)carboxylic acid, readily available from glucose. According to the computational prevision and confirmed by IR and NMR data, the insertion of 3-Ar-β-Morph in a model foldamer represents a way to stabilize a PPII-like helix through the presence of two γ-turns, secondary structure motifs induced by the morpholine ring, and the trans-tertiary amide bond.A facile and general strategy for efficient direct conversion of oximes to amides using an inexpensive organic photocatalyst and visible light is described. This radical Beckmann rearrangement can be performed under mild conditions. Various alkyl aryl ketoximes and diaryl ketoximes can be effectively converted into the corresponding amides in excellent yields.A modular approach has been developed for an efficient synthesis of an aminal group containing a new tetracyclic framework. The strategy has been devised based on selective hydrogen-bond-guided aza-Michael addition of heteroaromatic amines to cyclohexadienone-aldehydes. The reaction is highly atom economic and practical and involves stereoselective construction of four new C-N bonds and four rings. The synthetic utility of the tetracyclic product was explored. The role of a H-bond was explained with the help of experimental and density functional theory (DFT) computation studies.Optical imaging in the shortwave infrared region (SWIR, 1000-2000 nm) provides high-resolution images in complex systems. Here we explore substituent placement on dimethylamino flavylium polymethine dyes, a class of SWIR fluorophores. We find that the position of the substituent significantly affects the λmax and fluorescence quantum yield. Quantum-mechanical calculations suggest that steric clashes control the extent of π-conjugation. These insights provide design principles for the development of fluorophores for enhanced SWIR imaging.1,2-Cycloheptadiene is a strained, transient species that has been underutilized as a synthetic building block. Seven-membered cyclic allenes are mostly known for their propensity to undergo rapid dimerization, and relatively little has been reported regarding their cycloaddition reactivity with 1,3-dienes or 1,3-dipoles. This work describes the trapping of 1-acetoxy-1,2-cycloheptadiene and its unsubstituted counterpart, generated via desilylative elimination, with a range of 1,3-dipolar trapping partners, affording complex polycyclic products with high regio- and diastereoselectivity.The first base metal-catalyzed transfer hydrogenation of alkynes with methanol is described. An air and moisture stable manganese pincer complex catalyzes the reduction of a variety of different alkynes to the corresponding (Z)-olefins in high yields. The reaction is stereo- and chemoselective and scalable.A rhodium-catalyzed carbonylative transformation of unactivated phenols to aryl salicylates is described. This protocol is characterized by utilizing 1,3-rhodium migration as the key step to provide direct access to synthesize o-hydroxyaryl esters. Various desired aryl o-hydroxybenzoates were produced in moderate to excellent yields with bis(dicyclohexylphosphino)ethane (DCPE) as the ligand. Interestingly, diphenyl carbonate was formed as the main product when 1,3-bis(diphenylphosphino)propane (DPPP) was used as the ligand. A plausible reaction mechanism is proposed.Bond-breaking bio-orthogonal chemistry, consisting of a "click" reaction between trans-cyclooctene and tetrazine, followed by an intramolecular cyclization-driven uncaging step is described. The two-step process allows activation of caged compounds in biological media at neutral pH. The feasibility of this chemistry has been illustrated using NMR, while kinetics and pH-dependence were studied by fluorescence spectroscopy using caged coumarin. The practicality of the strategy is illustrated by activation of an anticancer drug, etoposide.Acylhydrazones formation has been widely applied in materials science and biolabeling. VE-822 However, their sluggish condensation rate under neutral conditions limits its application. Herein, indolines with electron-donating groups are reported as a new catalyst scaffold, which can catalyze acylhydrazone, hydrazone, and oxime formation via an iminium ion intermediate. This new type of catalyst showed up to 15-fold rate enhancement over the traditional aniline-catalyzed reaction at neutral conditions. The identified indoline catalyst was successfully applied in hydrogel formation.A Brønsted acid catalyzed cyclization of aminodiazoesters with aldehydes is described. This reaction features broad substrate generality and functional group compatibility, affording a wide range of 5-7-membered 3-carboxylate-N-heterocycles containing different functional groups. The title products are able to be further elaborated through simple functional group transformations to produce synthetically useful N-heterocycles.A highly enantioselective synthesis of α-branched acrylonitriles is reported featuring a one-pot sequential asymmetric Michael addition/retro-Dieckmann/retro-Michael fragmentation cascade. The method, which relies on a solid, bench-stable, and commercially available acrylonitrile surrogate, is practical, scalable, and highly versatile and provides a direct access to a wide range of enantioenriched nitrile-containing building blocks. Most importantly, the method offers a new tool to incorporate an acrylonitrile moiety in an asymmetric fashion.Solvent-controlled divergent domino annulation reactions between 2-hydroxy-2-methylchromene derivatives and prop-2-ynylsulfonium salts have been developed. Specifically, a sequential [4 + 2] and [4 + 2] annulation reaction occurred in 1,2-dichloroethane affording sulfur-containing benzo-fused dioxabicyclo[3.3.1]nonanes. In contrast, by changing the solvent to toluene, the reaction course switched to a [4 + 2] and [4 + 1] annulation reaction to afford dihydrofuro[2,3-c]chromenes. It is noteworthy that the prop-2-ynylsulfonium salt participates in the transformation with its γ-carbon atom for the first time.