Asymmetric tandem conjugate addition and reaction with carbocations on acylimidazole Michael acceptors.

We present here a stereoselective tandem reaction based on the asymmetric conjugate addition of dialkylzinc reagents to unsaturated acylimidazoles followed by trapping of the intermediate zinc enolate with carbocations. The use of a chiral NHC ligand provides chiral zinc enolates in high enantiomeric purities. These enolates are reacted with highly electrophilic onium compounds to afford densely substituted acylimidazoles. DFT calculations helped to understand the reactivity of the zinc enolates derived from acylimidazoles and allowed their comparison with metal enolates obtained by other conjugate addition reactions.

DNA-Based Asymmetric Inverse Electron-Demand Hetero-Diels-Alder.

While artificial cyclases hold great promise in chemical synthesis, this work presents the first example of a DNA-catalyzed inverse electron-demand hetero-Diels-Alder (IEDHDA) between dihydrofuran and various α,ß-unsaturated acyl imidazoles. The resulting fused bicyclic O,O-acetals containing three contiguous stereogenic centers are obtained in high yields (up to 99 %) and excellent diastereo- (up to >99:1 dr) and enantioselectivities (up to 95 % ee) using a low catalyst loading. Most importantly, these results show that the concept of DNA-based asymmetric catalysis can be expanded to new synthetic transformations offering an efficient, sustainable, and highly selective tool for the construction of chiral building blocks.

Synthetic Studies toward the Total Synthesis of Tautomycetin.

The studies culminating in the synthesis of two large subunits of tautomycetin are described. The first one, fragment C1-C12 that has an anti-1,3-dimethyl system and a terminal diene unit, was accomplished in 10 linear steps in 7.4% overall yield. The second one, fragment C13-C25 which bears the sensitive anhydride framework and the majority of the stereogenic centers, was prepared in 13 linear steps (longest sequence) in 8% overall yield. Among the key transformations used, a regioselective epoxide opening, a Pd-catalyzed addition of terminal alkyne to acceptor alkyne, a Mukaiyama aldol reaction, a Yamaguchi esterification, and a homemade mild di-esterification can be cited. The chosen strategies allowed good yields, stereoselectivity, reproducibility, and scalability for several important intermediates.

Non-Covalent Organocatalyzed Domino Reactions Involving Oxindoles: Recent Advances.

The ubiquitous presence of spirooxindole architectures with several functionalities and stereogenic centers in bioactive molecules has been appealing for the development of novel methodologies seeking their preparation in high yields and selectivities. Expansion and refinement in the field of asymmetric organocatalysis have made possible the development of straightforward strategies that address these two requisites. In this review, we illustrate the current state-of-the-art in the field of spirooxindole synthesis through the use of non-covalent organocatalysis. We aim to provide a concise overview of very recent methods that allow to the isolation of unique, densely and diversified spirocyclic oxindole derivatives with high structural diversity via the use of cascade, tandem and domino processes.

Copper-Catalyzed Asymmetric Conjugate Addition of Dimethylzinc to Acyl-N-methylimidazole Michael Acceptors: a Powerful Synthetic Platform.

An efficient copper-catalyzed enantioselective conjugate addition of dimethylzinc to α,ß- and α,ß,γ,δ-unsaturated 2-acyl-N-methylimidazoles has been achieved using a chiral bidentate hydroxyalkyl-NHC ligand. The reactions proceeded with both excellent regio- and enantioselectivity (14 examples, 87-95 % ee) to afford the desired 1,4-adducts, which were easily transformed to the corresponding aldehydes, esters, and ketones. Subsequently, this powerful methodology was therefore successfully applied in the synthesis of natural products. Furthermore, an iterative process was also disclosed leading to highly desirable 1,3-desoxypropionate skeletons (up to 94 % d.e.).

Inverse peptide synthesis via activated α-aminoesters.

A mild, practical, and simple procedure for peptide-bond formation is reported. Instead of activation of the carboxylic acid functionality, the reaction involves an unprecedented use of activated α-aminoesters. The method provides a straightforward entry to dipeptides and was effective when a sensitive cysteine residue was used, as no epimerization was detected in this case. The applicability of this method to iterative peptide synthesis was illustrated by the synthesis of a model tetrapeptide in the challenging reverse N→C direction.

Iron-Catalyzed Enantioselective Intramolecular Inverse Electron-Demand Hetero Diels-Alder Reactions: An Access to Bicyclic Dihydropyran Derivatives.

A highly enantioselective iron-catalyzed Intramolecular Inverse Electron-Demand Hetero Diels-Alder (IIEDHDA) reaction is reported. By using a chiral semicorrin ligand in the presence of 2,6-lutidine, good isolated yields and excellent enantioselectivities were observed (up to 96% ee). Thanks to the versatile postfunctionalization of the acyl-imidazole moiety, this methodology represents a unique example of the straightforward construction of highly valuable enantioenriched bicyclic dihydropyran derivatives.

Total Synthesis and Structure-Activity Relationships Study of Odilorhabdins, a New Class of Peptides Showing Potent Antibacterial Activity.

The spread of antibiotic-resistant pathogens is a growing concern, and new families of antibacterials are desperately needed. Odilorhabdins are a new class of antibacterial compounds that bind to the bacterial ribosome and kill bacteria through inhibition of the translation. NOSO-95C, one of the first member of this family, was synthesized for the first time, and then a structure-activity relationships study was performed to understand which groups are important for antibacterial activity and for inhibition of the bacterial translation. Based on this study an analogue showing improved properties compared to the parent compound was identified and showed promising in vitro and in vivo efficacy against Enterobacteriaceae.