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Stefan F Kirsch

Publications and source records attributed to Stefan F Kirsch.

11 recordsLinked to original sources
PubMed2006

Synthesis of stable 2H-pyran-5-carboxylates via a catalyzed propargyl-Claisen rearrangement/oxa-6pi electrocyclization strategy.

[reaction: see text] The application of easily accessed propargyl vinyl ethers for the synthesis of monocyclic 2H-pyrans was achieved. Under the reaction conditions, highly substituted heterocycles were obtained in moderate to excellent yields. The one-pot sequence proceeds via a Ag(I)-catalyzed propargyl-Claisen rearrangement, followed by a base-catalyzed isomerization, and 6pi-oxaelectrocyclization, leading to the formation of stable 2H-pyrans.

Journal Article↗
PubMed2006

Synthesis of highly substituted pyrroles via a multimetal-catalyzed rearrangement-condensation-cyclization domino approach.

[reaction: see text] In a convenient one-pot process, easily accessed propargyl vinyl ethers and aromatic amines are effectively converted into tetra- and pentasubstituted 5-methylpyrroles which can further be transformed into 5-formylpyrroles via IBX-mediated oxidation. The cascade reaction proceeds through a silver(I)-catalyzed propargyl-Claisen rearrangement, an amine condensation, and a gold(I)-catalyzed 5-exo-dig heterocyclization.

Journal Article↗
PubMed2006

Syntheses of polysubstituted furans: recent developments.

Despite attracting tremendous interest for well over a century, the field of furan syntheses is continuously and rapidly developing. This brief overview highlights recent progress in the syntheses of polysubstituted furans primarily guided by substitution pattern. Accordingly, methods are categorized as providing access to either di-, tri- or tetrasubstituted furans.

Cyclization↗
PubMed2005

Diastereoselective reactions at enantiomerically pure, sterically congested cyclohexanes as an entry to wailupemycins A and B: total synthesis of (+)-wailupemycin B.

Wailupemycin A (1) and B (2) are polyketide natural products with a highly substituted cyclohexanone core. Three different routes for the syntheses of these compounds were pursued, which commenced from either (R)-(-)-carvone (ent-5) or (S)-(+)-carvone (5). In the first approach it was attempted to construct the skeleton of wailupemycin A from triol 19 (nine steps from ent-5; 19 % yield) by a sequence of diastereoselective epoxidation, nucleophilic ring opening at C-13 and carbonyl addition at C-5. The synthetic plan failed at the stage of the carbonyl addition to aldehyde 27, which had been obtained in seven steps (18 % yield) from triol 19. The second route included an epoxide ring opening at C-13 and a carbonyl addition at C-7 as key steps. It could have led to either wailupemycin A or B depending on the diastereoselectivity of the addition step. Starting from allylic alcohol 30 (six steps from ent-5; 59 % yield) the cyclohexanone 28 was obtained in five steps (54 % yield). Unfortunately, the carbonyl addition failed also in this instance. In the eventually successful third attempt the skeleton of wailupemycin B was built from cyclohexanone 43 (eight steps from 5; 53 % yield) by highly diastereoselective carbonyl addition reactions at C-7 and C-12. The phenyl group at C-14 was introduced at a late stage of the synthetic sequence. Careful protecting group manipulation finally allowed for the total synthesis of (+)-wailupemycin B. The absolute and relative configuration of the natural product was unambiguously confirmed. The total yield of wailupemycin B amounted to 6 % over 23 steps starting from (S)-(+)-carvone (5).

Cyclohexanes↗
PubMed2005

Gold(I)-catalyzed synthesis of highly substituted furans.

Cationic triphenylphosphinegold(I) complexes are excellent catalysts for a cascade reaction of propargyl-Claisen rearrangement and heterocyclization to synthesize tri- and tetrasubstituted furans. Starting from easily accessed propargyl vinyl ethers, the furans are obtained in 72-99% yield. [reaction: see text]

Journal Article↗
PubMed2005

Catalytic asymmetric intramolecular aminopalladation: improved palladium(II) catalysts.

[reaction: see text] Cobalt oxazoline palladacyclic (COP) complex 4 containing acetate as a bridging ligand is an excellent catalyst for asymmetric intramolecular aminopalladation to synthesize 4-vinyloxazolidin-2-ones in 91-98% ee. In contrast to previously reported Pd(II) catalysts, COP-OAc (4) promotes the asymmetric cyclization of (Z)-allylic N-tosylcarbamates without prior activation by silver salts.

Journal Article↗
PubMed2005

Catalytic asymmetric synthesis of chiral allylic esters.

Trichloroacetimidate derivatives of prochiral (Z)-2-alken-1-ols react at room temperature with carboxylic acids to give chiral 3-acyloxy-1-alkenes in high enantiopurity in the presence of di-mu-acetatobis[(eta5-(S)-(pR)-2-(2'-(4'-methylethyl)oxazolinyl)cyclopentadienyl,1-C,3'-N)(eta4-tetraphenylcyclobutadiene)cobalt]dipalladium (COP-OAc) or its enantiomer. This reaction has broad scope, proceeds with predictable high stereoinduction, is accomplished at room temperature using high substrate concentrations and low catalyst loadings, and likely proceeds by a novel mechanism.

Acetamides↗
PubMed2004

Monomeric cobalt oxazoline palladacycles (COP). Useful catalysts for catalytic asymmetric rearrangement of allylic trichloroacetimidates.

Cobalt oxazoline palladacycles (COP) containing acetylacetonate and hexafluoroacetylacetonate ligands were prepared as catalysts for the asymmetric rearrangement of allylic trichloroacetimidates. These monomeric catalysts are more soluble than the previously described chloride-bridged dimer COP-Cl (1). COP-hfacac (2) provides rearranged allylic trichloroacetamides with high enantiomeric purities (91-98% ee) in solvents of widely varying polarities: cyclohexane, toluene, 1,2-dichloroethane, ethyl acetate, acetone, acetonitrile, and THF. The first single-crystal X-ray structure of a COP catalyst is also reported.

Journal Article↗