Mette Lene Falck-Pedersen

Asymmetric synthesis of phenylbis(glycines)

Abstract ( S , S )- α , α ′-Diamino-1,4- and 1,3-benzenediacetic acids and N -Boc- and N -Fmoc-derivatives have been prepared by stereoselective syntheses. The chiral auxiliary ( S )-4-benzyl-2-oxazolidinone formed bisimides with benzenediacetyl dichlorides The imides were lithiated at both α-sites to the carbonyl groups and azidated stereoselectively alpha to both carbonyl groups by trisyl azide to provide ( S , S )- α , α ′-diazidobenzenediacetic acid derivatives which were reduced to amines by Sn(II) chloride or by hydrogenolysis over Pd.

Synthesis of silacycloalkenes and silaspirenes by Ru(II)-catalyzed ring-closing metathesis reactions

Abstract Cyclisation reactions of dienyl- and enynylsilanes by carbon–carbon bond formation under RCM conditions yield five-, six- and seven-membered silacycloalkenes. The relative ease of ring formation from dienes was in the order six->seven->five-membered rings. A conjugated vinylsilacyclopentene was formed from the corresponding enyne substrate. Silaspirenes have been prepared from silacarbacycles by the same methodology. Cyclisations effected under radical conditions gave complimentary silacycloheptane and silacycloheptene products. The ring closure proceeded by the endo-trig route.

Palladium-mediated carbosubstitutions in spiranes

Abstract Carbosubstitutions in spirene triflates can be effected by Pd-catalyzed couplings with stannylated or zincated arenes. Differential carbosubstitution resulted from stepwise triflation and coupling in spiro[4,4]-nonane-1,6-dione. Catalytic hydrogenation of the 1,6-diphenyl-1,6-diene gave the cis,cis-disubstituted spirane. Metal hydride reduction of intermediate monoketone gave mainly the cis-alcohol.

Palladium mediated substitutions and rearrangements in spiro[4,4]nonanes

Abstract The two-step NaBH 4 CeCl 3 1,2-reduction of spiro[4,4]nonane-2,7-diene-1,6-dione gave a rans-alcohol as a first product which reacted further to the corresponding cis,trans-diol. Pd(II)-catalysis was used to effect an allylic rearrangement from the 1,6-diacetate to the corresponding 2,7-diacetate. Both diacetates were substrates for Pd(0)-catalyzed allylic alkylations. The relative stereochemistry was retained.

THE PAUSON-KHAND REACTION IN SYNTHESIS OF BICYCLIC RIGID α-AMINO ACIDS

The combination of intramolecular Pauson-Khand methodology for Co2(CO)8 mediated cyclization, and the Schöllkopf chiral auxiliary for stereoselective preparation of appropriate 1,6-heptenynes constitutes a powerful method for the preparation of rigidified bicyclic α-amino acids.

Stereoselectivity in the synthesis of conformationally constrained vicinally dihydroxylated cyclic α-amino acids

Stereoselective syntheses of precursors to vicinal cis-dihydroxy-1-aminocyclopentane- and -cyclohexane-carboxylic acid methyl esters and their methoxy analogues are described. The chiral products are isolated as pure enantiomers. The absolute configurations at the new stereogenic centres are established by X-ray analysis.