Dual stereoselectivity in the dialkylzinc reaction using (-)-beta-pinene derived amino alcohol chiral auxiliaries.

(+)-Nopinone, prepared from naturally occurring (-)-beta-pinene, was converted to the two regioisomeric amino alcohols 3-MAP and 2-MAP in very good yield and excellent isomeric purity. Amino alcohol 3-MAP was synthesized by converting (+)-nopinone to the corresponding alpha-ketooxime. This was reduced to the primary amino alcohol and was converted to the morpholino group through a simple substitution reaction. 3-MAP was characterized by X-ray crystallography, which displayed the rigidity of the pinane framework. Amino alcohol 2-MAP was prepared from its trans isomer 2, which in turn was synthesized via hydroboration/oxidation of the morpholine enamine of (+)-nopinone. Two-dimensional NMR was used to characterize amino alcohol 2-MAP, and NOE was used to confirm its relative stereochemistry. These amino alcohols were employed as chiral auxiliaries in the addition of diethylzinc to benzaldehyde to obtain near-quantitative asymmetric induction in the products. The use of 3-MAP yielded (S)-phenylpropanol in 99% ee, and its regioisomer 2-MAP gave the opposite enantiomer, (R)-phenylpropanol, also in 99% ee. Other aromatic, aliphatic, and alpha,beta-unsaturated aldehydes were implemented in this method, affording secondary alcohols in high yield and enantiomeric excess. Amino alcohols 2-MAP and 3-MAP were also found to be useful in the dimethylzinc addition reaction, both catalyzing the addition to benzaldehyde with nearly quantitative ee. Regioisomeric amino alcohols 2-MAP and 3-MAP, even though they were prepared from one enantiomer of nopinone, provide antipodal enantiofacial selectivity in the dialkylzinc addition reaction. This circumvents the necessity to synthesize amino alcohols derived from (-)-nopinone, which in turn requires the unnatural (+)-beta-pinene. Possible mechanistic insights are offered to explain the dual stereoselectivity observed in the diethylzinc addition reaction involving regioisomeric, pseudo-enantiomeric amino alcohols 3-MAP and 2-MAP.

Lewis acid-catalyzed one-pot, three-component route to chiral 3,3'-bipyrroles.

3,3'-Bipyrroles 3 could be synthesized using a double Michael addition reaction involving diaroyl acetylene 1 and the appropriate 1,3-dicarbonyls 2 using ammonium acetate as a nitrogen source. The axial chirality of bipyrrole was anticipated from the X-ray crystal structure and DFT calculations and confirmed by separating the racemates on a chiral column and subsequent CD spectra of the enantiomers. The absolute configuration of the enantiomers was achieved by theoretical CD spectra calculation using the ZINDO method.

Synthesis of arylboronates by the palladium catalysed cross-coupling reaction in ionic liquids.

The palladium catalysed cross-coupling reaction of aryl iodides and bromides with pinacolborane in 1,3-dialkylimidazolium tetrafluoroborates and hexafluorophosphates producing arylboronates is described.