Fabien Boeda

Ruthenium-indenylidene complexes: powerful tools for metathesis transformations.

Ruthenium-indenylidene complexes represent a class of robust and efficient pre-catalysts for olefin metathesis reactions. In this feature article, we provide an overview of the various complexes belonging to this family and summarise their use in various applications. The relation between the nature of ancillary ligands around the metal coordination sphere of these complexes and their catalytic activity is also discussed.

Enantioselective Intramolecular Hydroamination of Secondary Amines Catalyzed by Easily Accessible Ate and Neutral Rare‐Earth Complexes

Intramolecular catalytic asymmetric hydroamination of unactivated olefins is currently the subject of extensive research as one of the more elegant, environmentally friendly, and atomeconomical methods for the formation of enantioenriched and value-added nitrogen-containing heterocycles. Despite significant achievements in this challenging field, no general answer has yet emerged, and considerable improvements are still required to bring this attractive method into the organic chemist’s toolbox as a pivotal tool to create C N bonds. Indeed, amongst the diversity of reported catalytic systems, only a very limited number, based on rare-earth, lithium, zirconium, or rhodium, affords a high level of enantioselectivity (>90 % ee) for hydroamination/cyclization reactions of amines tethered to unactivated alkenes. 7, 8] Moreover, these highly enantioselective catalytic systems derived from neutral zirconium amidate and MOP–rhodium complexes (MOP = 2-(diarylphosphino)-2’-methoxy-1,1’-binaphthalene) are respectively restricted to primary or secondary amines, affording, correspondingly, no or poor reactivity with secondary and primary amines. 10] An alternative cationic zirconium complex bearing an aminophenolate ligand as a chiral scaffold was already reported for the hydroamination/cyclization of N-methylated amines to unactivated olefins with up to 82 % ee. The catalytic system derived from lithium and based on chiral (bis)oxazoline ligands has only been reported for the enantioselective hydroamination of N-methylated aminoalkenes. To date, the highest ee value (95 %) was achieved using a sophisticated substituted binaphtholate rare-earth complex for intramolecular hydroamination of a primary amine, whereas lower asymmetric induction was observed with a secondary amine. A chiral aminobis(thio)phenolate yttrium complex was previously demonstrated to catalyze the enantioselective intramolecular addition of primary and secondary amines to unactivated alkenes, exhibiting a similar trend in terms of level of enantioselectivity (80–87 % ee for primary amines and 69 % ee for a secondary amine). To our knowledge, this last ee value is the highest reported to date for a rare-earth-catalyzed hydroamination of a secondary amine. In this context, we report herein the in situ preparation of chiral binaphthylamido alkyl ate and neutral yttrium and ytterbium complexes and their use as highly active catalysts for the intramolecular hydroamination of secondary amines. Our group has long been interested in the development of chiral well-defined binaphthylamido ate and neutral rare-earth complexes as catalysts for the asymmetric intramolecular hydroamination of primary aminoalkenes. These ongoing studies have identified neutral and ate heteroleptic binaphthylamido alkyl yttrium and ytterbium complexes as the most promising candidates for the development of efficient and easily accessible chiral catalysts by a convenient procedure. Very recently, we reported a novel “single-pot” route for the rapid in situ generation of ate yttrium complexes from the stable and straightforwardly synthesized rare-earth precursor [Li(thf)4] [Y(CH2SiMe3)4] [12] 1-Y. This very reliable process showed its ability to afford active and enantioselective (pre)catalysts for the intramolecular hydroamination/cyclization of challenging substrates such as primary amines tethered to unactivated 1,2-disubstituted alkenes. Herein we report a similar strategy to easily access neutral binaphthylamido alkyl yttrium and ytterbium analogues from a related homoleptic rare-earth source [Ln(CH2SiMe3)3(thf)2] [13] (2-Ln; Ln = Y or Yb). We describe the potential of these neutral and ate rare-earth catalysts to promote the intramolecular hydroamination of secondary amines tethered to monosubstituted olefins. The catalytic activities of corresponding chiral species arising from coordination to an enantiopure binaphthyldiamine ligand were then evaluated for the transformation of the same substrates. To date, the highest enantiomeric excesses for the cyclization of primary aminoolefins catalyzed by ate tetraamido and ate amido alkyl rare earth complexes were measured using N-cyclopentyl binaphthyl amine ligand L (Scheme 2). This diamine was thus chosen for this study. The activities of the tetraalkyl ate yttrium precursor 1-Y and trisalkyl neutral precursors 2-Y and 2-Yb were firstly

Efficient Synthesis of New Nucleoside Analogues with a Methylenecyclobutane Unit

Abstract Synthesis of eight nucleoside analogues 4–11 with a methylenecyclobutane unit is described. Wittig reaction with 2‐hydroxymethylcyclobutanone 12 gave a mixture of Z (13) and E (14) derivatives, which was separated before functional modifications. The heterocyclic moieties were introduced via a Mitsunobu reaction either on the saturated chain or on the unsaturated chain. When adenine was used in this reaction, only the N‐9 substitution products were obtained. Removal of the protecting groups provided the target products.

Ionic liquid supported organotin reagents to prepare molecular imaging and therapy agents

Efficiency of ionic liquid supported organotin reagents in halodemetalation reaction has been investigated. High radiochemical yields of astatinated and iodinated compounds have been obtained using simple work-up procedure. This methodology represents a straightforward approach for the preparation of molecular imaging and therapy agents in nuclear medicine.

Synthesis and biological evaluation of 3-cyano-4H-chromene derivatives bearing carbamate functionality

BACKGROUND 2-Aminochromene derivatives display important pharmacological properties, including mainly antibiotic and anticancer activities. OBJECTIVE The study aims to synthesize new chromene derivatives via a new approach using Grignard reagents, for the evaluation of their antibiotic and antifungal properties. METHOD A series of novel 3-cyano-4-aminochromene derivatives bearing alkyl substituents at the 4-position was prepared for biological evaluation. RESULTS These compounds were obtained by the addition of various Grignard reagents into Nethoxycarbonyl- 3-cyanoiminocoumarines in moderate to good yields (72-96%). The reaction is completely regioselective. The new chromene derivatives were screened for their in vitro antimicrobial activities against a panel of six bacterial and three fungal strains using agar dilution method. CONCLUSION The antibacterial activity of the chromene derivatives was more pronounced on Gram-positive bacteria than on Gram-negative bacteria with a significant activity observed against Staphylococcus aureus. An interesting antifungal activity against Fusarium sp. and Fusarium oxysporum was also noticed.

Chapter 7:Titanium-based Catalysts for Asymmetric Transformations

Titanium is employed in a wide range of important enantioselective reactions, including epoxidations, reductions, nucleophilic additions, and cycloadditions. This chapter summarises the most important catalytic systems employed in these reactions and the sustainable aspects developed thereof. In particular, efforts to reduce the amount of catalyst (or the ligand) or the use of supported heterogeneous and homogeneous catalysts are described.