Annie-Claude Gaumont

Ionic liquids and chirality: opportunities and challenges

This review deals with recent advances in the investigation of ionic liquids (ILs) in the field of chirality, i.e. asymmetric synthesis and new chiral solvents.

Ionic Liquids: New Targets and Media for α-Amino Acid and Peptide Chemistry

CNRS-UMR 5068, LSPCMIB, Universite Paul Sabatier, 118 route de Narbonne, F-31062 Toulouse Cedex 9, France, Laboratoire de Chimie Moleculaire et Thio-organique, ENSICAEN, Universite de Caen Basse-Normandie, FR CNRS 3038, 6 boulevard du Marechal Juin, F-14050 Caen, France, CNRS-UMR 6014, IRCOF, Universite de Rouen, rue Tesniere, F-76821 Mont-Saint-Aignan Cedex, France, and URCOM, EA 3221 FR CNRS 3038, Universite du Havre, 25 rue Ph. Lebon, BP 540, F-76058 Le Havre Cedex, France

Overview of the Chemistry of 2-Thiazolines

Heterocyclic compounds are of outstanding importance as pharmaceuticals, agrochemicals, fine and bulk chemicals, and ligands for catalysis.1 Among the different heterocycles, 2-oxazolines have been widely studied and reviewed,2 especially chiral oxazolines3 and bis(oxazolines),4 due to their wide application as ligands for asymmetric catalysis. Compared to 2-oxazolines, the sulfur analogues, that is, the 2-thiazolines, have received less attention. To the best of our knowledge, there is only one review, published by Fustero et al. in 2001,5 which focuses on the preparation and to some extent synthetic applications of both 2-alkyl2-thiazolines and 2-alkyl-2-oxazolines. Recently, various groups have paid attention to the chemical properties of 2-thiazolines, mainly because of the unique properties of sulfur. In different reports, a reactivity that often dramatically differs from that of the corresponding oxazoline derivatives was pointed out. In this contribution, we wish to give an overview of the chemistry of 2-thiazolines, including new methodologies for their preparation, and recent applications, such as their growing use in organic synthesis in the biological field and asymmetric catalysis as ligands. The methods enabling access to thiazolines will first be underlined. Then the reactivity and applications in the fields of organic synthesis, biomolecules (natural or not), and catalysis will be documented. The structure of the thiazolines treated in this review is illustrated in Figure 1. Compounds bearing atoms other than carbon at the 2-position, including 2-H-thiazolines, 2-aminothiazolines, or 2-halogenothiazolines, are beyond the scope of this review. Cited references are restricted to journals, reviews, and books. Literature coverage for this review extends up to September 2007.

Metal-Free, Visible Light-Photocatalyzed Synthesis of Benzo[b]phosphole Oxides: Synthetic and Mechanistic Investigations

Highly functionalized benzo[b]phosphole oxides were synthesized from reactions of arylphosphine oxides with alkynes under photocatalytic conditions by using eosin Y as the catalyst and N-ethoxy-2-methylpyridinium tetrafluoroborate as the oxidant. The reaction works under mild conditions and has a broad substrate scope. Mechanistic investigations have been undertaken and revealed the formation of a ground state electron donor-acceptor complex (EDA) between eosin (the photocatalyst) and the pyridinium salt (the oxidation agent). This complex, which has been fully characterized both in the solid state and in solution, turned out to exhibit a dual role, i.e., the oxidation of the photocatalyst and the formation of the initiating radicals, which undergoes an intramolecular reaction avoiding the classical diffusion between the two reactants. The involvement of ethoxy and phosphinoyl radicals in the photoreaction has unequivocally been evidenced by EPR spectroscopy.

B(C6F5)3-catalyzed formation of B–P bonds by dehydrocoupling of phosphine–boranes

Tris(pentafluorophenyl)borane was used as a new catalyst in the formation of P-B bonds by dehydrocoupling of phosphine-boranes.

Pallado-catalysed hydrophosphination of alkynes: access to enantio-enriched P-stereogenic vinyl phosphine–boranes

Preliminary results dealing with the synthesis of non-racemic P-stereogenic vinylphosphine-boranes by hydrophosphination of alkynes in the presence of a chiral catalyst are reported.

Synthesis and properties of thiazoline based ionic liquids derived from the chiral pool

A novel class of chiral ionic liquids derived from amino alcohols is prepared in multi-gram scale. Their potential in chiral recognition is shown in a preliminary example with racemic Moshers acid salt.

Development of new SILP catalysts using chitosan as support

New SILP catalysts based on chitosan-supported ionic liquid were successfully applied to allylic substitution reactions. A high level of activity combined with recyclability and reusability were obtained in the amination reaction. No organic solvent was used. The scope and limitations of the reaction using these new SILP catalysts were estimated.

Iron‐Salt‐Promoted Highly Regioselective α and β Hydrophosphination of Alkenyl Arenes

and reagents in organic synthesis. However, due to the high energy of the P H bond (E=77 kcal mol ), the reaction usually requires activation by radical initiators. Thermal-, acid-, and base-promoted reactions have also been applied, although less frequently. Metaland lanthanide-catalyzed processes were also reported recently. Whatever the method, the addition usually proceeds in an anti-Markovnikov way leading to the b adduct B (addition of the phosphorus atom to the terminal carbon atom of a terminal alkene). In contrast, the selective formation of the valuable a adduct A, with formation of a stereogenic centre, is still a challenging problem. In addition, examples of styrenic hydrophosphination are scarce. Addition to styrene was reported under basic, and radical conditions and more recently by using transition-metal catalysts (Ni, Cu). All these procedures afforded anti-Markovnikov adducts. Inexpensive and environmentally friendly iron salts have recently emerged as powerful tools in organic synthesis. Their efficiency has been demonstrated in several addition reactions to carbon–carbon double bonds (hydroamination, hydrothiolation, hydroboration, hydrosilylation, hydroarylation, and oxyphosphorylation) and during the course of our studies in the double hydrophosphination of terminal arylacetylenes. As part of our ongoing studies of the control of the regioselectivity of hydrophosphination reactions, 23] herein we report the iron-promoted hydrophosphination reaction of styrenes, which offers selective access to either the b adduct B or the a adduct A (Schemes 1 and 2).

Ph2P(BH3)Li: From Ditopicity to Dual Reactivity

A multinuclear NMR study shows that the deprotonation of diphenylphosphine-borane by n-BuLi in THF leads to a disolvated lithium phosphido-borane Ph(2)P(BH(3))Li of which Li(+) is connected to the hydrides on the boron and two THF molecules rather than to the phosphorus. This entity behaves as both a phosphination and a reducing agent, depending on the kinetic or thermodynamic control imposed to the reaction medium. Density functional theory computations show that H(2)P(BH(3))Li exhibits a ditopic character (the lithium cation can be in the vicinity of the hydride or of the phosphorus). It explains its dual reactivity (H- or P-addition), both routes going through somewhat similar six-membered transition states with low activation barriers.