H. Hogeveen

Enantioselective addition of n-butyllithium to benzaldehyde in the presence of chiral lithium amides

Abstract The reaction of n-butyllithium with benzaldehyde in the presence of chiral lithium amides 1a-–e gives 1-phenyl-1-pentanol with optical yields up to 90%.

Enantioselective deprotonation of two racemic cyclic carbonyl compounds by a chiral lithium amide

Abstract The cyclic carbonyl compounds 2 and 8 have been obtained in optical active form (o. y. 46% and 36%, respectively) from the racemic compounds by a deprotonation/protonation sequence using chiral lithium amide 1 . The optical activity of 2 is caused by a difference in the deprotonation rates of the enantiomers.

Enantioselective protonation of a prochiral bicyclobutane bridged enolate anion

Abstract Protonation of bicyclobutane bridged enolate anion 2 , formed from ketone 1 and lithium (S,S)-α,α′-dimethyldibenzylamide, has yielded optically active ketone 1 (e.e. 48%).

Enantioselective carboxylation of a prochiral enolate in the presence of a chiral lithium amide

Abstract The prochiral lithium 2,2,6-trimethylcyclohexenolate ( 2 ) was prepared from ketone 1 by deprotonation with lithium (S,S)-α,α′-dimethyldibenzylamide ( 4 ). Reaction of 2 with carbon dioxide at low temperature followed by methylation with methyl iodide yielded the corresponding ester 3 with an e.e. of 67%.

TETRAMETHYLCYCLOBUTADIENE RADICAL CATION

Abstract The tetramethylcyclobutadiene radical cation has been generated photochemically in solutions of aluminum halide σ complexes of tetramethylcyclobutadiene. It decays thermally to a “dimeric” radical cation.

Towards persistent cyclobutadiene radical cations? The tetra-1-adamantyl-, and tetraneopentylcyclobutadiene radical cations.

Abstract The persistence of alkyl substituted cyclobutadiene radical cations strongly depends on the method of generation and the size of the alkyl substituents used. Hindered rotation, the consequence of bulky substituents, is observed in the title compounds.

ENANTIOSELECTIVE REDUCTION OF ACETOPHENONE BY BORANE - CHIRAL AMINE COMPLEXES

The enantioselective reduction of acetophenone by the borane.chiral amine complexes BH3.1a - BH3.1d affords 1-phenyl-1-ethanol with o.y. up to 42%.

Cyclic delocalized 3 Π-electron systems. An ESR spectroscopic investigation of some tetra alkyl-substituted cyclobutadiene radical cations.

Abstract Tetra alkyl-substituted cyclobutadiene radical cations are Π- and not σ-radicals. This can be concluded from the ESR spectra of the tetramethylcyclobutadiene radical cation at low temperatures, and from the 13 C hyperfine splitting constants of the tetraethylcyclobutadiene radical cation.

PREPARATION OF 1,3-DIALKYNYLADAMANTANES AND THEIR ALUMINUM BROMIDE-MEDIATED CYCLOADDITION ADDUCTS

Summary The synthesis of 1,3-diethynyl- ( 1 ) and 1,3-di(1-propynyl)adamantane 2) is reported. The aluminum bromide induced cocyclodimerization of 2 with propyne affords the dinuclear σ complex 7 , and the cyclodimerization of 1 the polynuclear σ complex 8 .

Reversible and irreversible processes in alkyne - AlBr3 chemistry

Abstract NMR line-broadening has shown the existence of a rapid exchange between 2-butyne and 2-butyne-AlBr 3 π complex. The AlBr 3 -induced heterocyclodimerization of 2-butyne with propyne is preferred to the corresponding homo-cyclodimerisations.