Marie E. Krafft

Regiospecific preparation of thermodynamic silyl enol ethers using bromomagnesium dialkylamides

Abstract Theromodynamic silyl enol ethers are regiospecifically generated in high yield from cyclic ketones, bromomagnesium diisopropylamide (BMDA) and trimethysilyl chloride.

Synthesis of medium-sized rings using the intramolecular Pauson–Khand reaction

Abstract The dicobalthexacarbonyl alkyne complex of a series of enynes templated on aromatic rings has been shown to undergo the Pauson–Khand reaction to generate medium-sized rings.

Modification and limitations of the Livinghouse catalytic Pauson-Khand reaction

Abstract The difficult and impractical purification of Co 2 (CO) 8 is not necessary in the catalytic thermal Pauson-Khand reaction previously described by Livinghouse.

Cobalt-catalyzed homocoupling of terminal alkynes: synthesis of 1,3-diynes

Abstract Homocoupling of terminal alkynes proceeds using Co 2 (CO) 8 pretreated with phenanthroline to give good yields of 1,3-diynes under mild conditions.

Gold(I)-catalyzed Claisen rearrangement of allenyl vinyl ethers; synthesis of substituted 1,3-dienes.

Synthesis of substituted 1,3-dienes was achieved via gold(I)-catalyzed Claisen rearrangement of allenyl vinyl ethers. The N-heterocyclic carbene gold chloride catalyst (IPrAuCl) was superior in terms of activity and selectivity and afforded the 3,3-product in excellent yields. A proposed cation-π inter-action played a significant role in affecting the reaction rate.

New directions for the Morita−Baylis–Hillman reaction; homologous aldol adducts via epoxide opening

Under trialkylphosphine catalyzed Morita-Baylis-Hillman reaction conditions, epoxides react with enones to give rise to homologous aldol adducts.

Catalyst precursors for the catalytic Pauson-Khand reaction

Dicobalt hexacarbonyl complexes of enynes serve as Co2(CO)8 surrogates for the intramolecular Pauson-Khand cycloaddition. Enynes with polar functional groups allow for easy separation of the catalyst cyclopentenone by-product (acid or base wash, silica gel plug column) from the desired cyclopentenone.

Steric control in the pauson cycloaddition: Further support for the proposed mechanism

Abstract Dicobalthexacarbonyl complexes of internal alkynes react with olefins to give cyclopentenones with a high degree of regiocontrol. Analogous reactions of terminal alkynes give rise to regioisomeric mixtures of cyclopentenones.

STEREOSELECTIVITY IN THE INTRAMOLECULAR PAUSON-KHAND REACTION : TOWARDS A SIMPLE PREDICTIVE MODEL

Abstract The major product in the intramolecular Pauson-Khand reaction of 3,4-disubstituted 1,6-heptenynes to form bicyclo[3.3.0]octenones is highly dependent on the relative configurations of the two stereocenters of the substrate. For example, cycloaddition of the “syn,syn” stereoisomer of 3,5-dimethyl-4-propargyl-1,6-heptadiene gives predominantly an enone containing both substituents in more hindered endo orientations; the “syn,anti” stereoisomer, upon reaction across the “syn” linkage similarly gives mostly endo product, but upon reaction across the “anti” portion of the molecule affords almost exclusively an enone in which the C6 methyl group possesses exo stereochemistry. Parallel results obtain from enynes built upon cyclohexane frameworks. Calculated energies of pre-cycloaddition enynes, metallacycles presumed to be the penultimate intermediates in the cyclization mechanism, and the final products are examined in order to develop a reasonable predictive model.

DIENES FROM THE THERMOLYSIS OF DICOBALTHEXACARBONYL-COMPLEXED ENYNES : MECHANISTIC INSIGHT

Abstract Thermolysis of the hexacarbonyldicobalt complex of 1,6- or 1,7-enynes yields monocyclic 1,3-dienes. Deuterium labeling studies rule out an α-elimination as the mechanistic pathway for diene formation.