Preparation of new axially chiral bridged 2,2′-bipyridines and pyridyl monooxazolines (pymox). Evaluation in copper(i)-catalyzed enantioselective cyclopropanation

Renaissance of pyridine-oxazolines as chiral ligands for asymmetric catalysis

Oxazoline-containing ligands have been widely employed in numerous asymmetric catalytic reactions. Pyridine-oxazoline-type ligands, a class of hybrid ligands, were designed earlier than bisoxazoline and phosphine-oxazoline ligands; however, their unique properties have only been discovered recently. Pyridine-oxazoline-type chiral ligands are rapidly becoming popular for use in asymmetric catalysis, especially for several new and efficient asymmetric methodologies. Several types of challenging asymmetric reactions have been discovered recently using pyridine-oxazoline-type ligands showing their special properties and potential for future application in a wide range of new catalytic methodologies. This review provides an overview of this field, with the aim of highlighting both ligand design and synthetic methodology development.

Conformational and Optical Characteristics of Unidirectionally Twisted Binaphthyl-Bipyridyl Cyclic Dyads

An axially chiral binaphthyl-bipyridyl cyclic dyad in which the two units are connected by short -CH2O- linkers was synthesized. Experimental and theoretical analyses indicate that the (R)-binaphthyl unit in the dyad induces (R)-chirality in the bipyridyl unit, both in the solid state and in solution. It is shown that vibrational circular dichroism (VCD) is useful to determine the twisting pattern of 2,2'-bipyridyl compounds. The dyad shows crystallization-induced emission enhancement (CIEE).

Selective Stille coupling reactions of 3-chloro-5-halo(pseudohalo)-4H-1,2,6-thiadiazin-4-ones

A series of 3-chloro-5-halo(pseudohalo)-4H-1,2,6-thiadiazin-4-ones (halo/pseudohalo = Br, I, OTf) are prepared from 3,5-dichloro-4H-1,2,6-thiadiazin-4-one (3) in good yields. Of these the triflate reacts with tributyltin arenes (Stille couplings) chemoselectively to give only the 5-aryl-3-chloro-4H-1,2,6-thiadiazin-4-ones in high yields. This allowed the preparation of a series of unsymmetrical biaryl thiadiazines and ultimately a series of oligomers. Furthermore, treatment of 3-chloro-5-iodo-4H-1,2,6-thiadiazin-4-one (10) with Bu(3)SnH and Pd(OAc)(2) gave the bithiadiazinone which can also be further arylated via the Stille reaction to give bisthien-2-yl and bis(N-methylpyrrol-2-yl) analogs.