From cationic to anionic helicenes: new reactivity through umpolung.

Using a two-step reduction/metalation procedure, highly stable chiral carbenium ions are transformed into reactive carbanion intermediates. Interesting polar ketone and thioamide products are the results of this umpolung that occurs with complete retention of configuration of the helical backbone.

Intermolecular Heck-type coupling of aryl iodides and allylic acetates.

[reaction: see text] A palladium-catalyzed arylation of allylic acetates followed by beta-acetoxy elimination was shown to produce Heck-type coupling products. Optimal reaction conditions employed ligand-free palladium on carbon in the presence of tetrabutylammonium chloride, a trialkylamine base, and water.

Palladium-catalyzed intramolecular coupling between aryl iodides and allyl moieties via thermal and microwave-assisted conditions.

Palladium-catalyzed intramolecular cross-coupling reactions between aryl iodides and allyl moieties were successfully demonstrated in the presence of palladium catalyst, tri-o-tolylphosphine, a tertiary amine, and water. Several kinds of trans-2,4-disubstituted 1,2,3,4-tetrahydroquinolines were synthesized in 73-88% yields with excellent diastereoselectivities. This method was further applied to a large variety of substrates to form five-, six-, and seven-membered carbo- and heterocycles in good yields, regardless of the ring-containing atom, via microwave-assisted conditions.

1H, (19)F, and (31)P PGSE NMR diffusion studies on chiral organic salts: ion pairing and the dependence of a diffusion value on diastereomeric structure.

1H, (19)F and (31)P pulsed field gradient spin-echo (PGSE) diffusion studies on chiral organic salts that contain hexacoordinate phosphate anions, namely tris(tetrachlorobenzenediolato)phosphate(V) (TRISPHAT) and bis(tetrachlorobenzenediolato)mono([1,1']binaphthalenyl-2,2'diolato)-phosphate(V) (BINPHAT), are reported. The first example of the dependence of a diffusion value on diastereomeric structure is presented. Marked solvent and concentration effects on the diffusion constants (D) of these salts are noted and the question of ion pairing is discussed.

Bent structure and dynamic stereochemistry of chiral acridinium cations.

Chiral acridinium cations, easily prepared by reaction of enantiopure primary amines and tris(2,6-dimethoxy)trityl cation, display restricted rotations around the C(sp(3))-N(sp(2)) bond. A bending of the aromatic backbone and "out-of-plane" displacements of C(9) and N(10) atoms are enforced if bulky amines are introduced.

Efficient NMR enantiodifferentiation of chiral quats with BINPHAT anion.

Hexacoordinated phosphorus BINPHAT anion is an efficient NMR chiral shift agent for quaternary ammonium cations (quats) leading to large separations (DeltaDeltadelta up to 0.29 ppm) of the proton signals of the enantiomers. [reaction: see text]