RESUMO
The reaction conditions and scope of the excited-state Nazarov reaction of dicyclicvinyl ketones were studied. The stereochemistry of this electrocyclization is consistent with the mechanism of the pericyclic reaction and Woodward-Hoffmann rule. UV-light-promoted excited-state Nazarov reactions gave hydrofluorenones bearing a syn-cis configuration via a disrotatory cyclization. The core tricyclic hydrofluorenones of pyrrocidines and wortmannines were constructed via the excited-state Nazarov reactions, which demonstrated their synthetic potential in complex natural product total synthesis.
RESUMO
The asymmetric total synthesis of farnesin, a rearranged ent-kaurenoid, was achieved through a convergent approach involving photo-Nazarov and intramolecular aldol cyclizations to build the syn-syn-syn hydrofluorenol ABC ring system and bicyclo[3.2.1]octane CD ring system in the first application of a UV-light-induced excited-state Nazarov cyclization of a non-aromatic dicyclic divinyl ketone in a total synthesis. Unlike the conventional acid-promoted ground-state Nazarov reaction, the excited-state Nazarov reaction enables stereospecific formation of the highly strained syn-syn-syn-fused hydrofluorenone scaffold through a disrotatory cyclization.
RESUMO
An NHC-triggered, transition-metal-free strategy for the efficient synthesis of 2,3-disubstituted benzofuran derivatives in moderate to excellent yields from aryl or alkyl aldehydes and o-quinone methides has been developed. This method features mild reaction conditions, operational simplicity, broad substrate scope and convergent assembly.
RESUMO
A straightforward N-heterocyclic carbene (NHC)/LiCl-mediated synthesis of dihydropyranones from α,ß-unsaturated carboxylic acids and 1,3-dicarbonyl compounds was realized through the in situ activation strategy. The key advantages of this protocol include ready availability and high stability of starting materials, good yields, and excellent enantioselectivity.
Assuntos
Ácidos Carboxílicos/química , Compostos Heterocíclicos/química , Cloreto de Lítio/química , Metano/análogos & derivados , Pironas/síntese química , Ácidos Carboxílicos/síntese química , Catálise , Compostos Heterocíclicos/síntese química , Metano/síntese química , Metano/química , Pironas/química , EstereoisomerismoRESUMO
An N-Heterocyclic Carbene (NHC)-catalyzed oxidative formal [4 + 2] annulation of acylhydrazones with saturated carboxylic acids bearing γ-H to assemble δ-lactams featuring a chiral carbon stereogenic center was developed through an in situ activation strategy. The ready availability of the starting materials, excellent enantioselectivity, facile assembly, high yields, and potential biological significance of the final products make this protocol an attractive alternative for the construction of the pyridinone scaffold.
Assuntos
Ácidos Carboxílicos/química , Lactamas/síntese química , Metano/análogos & derivados , Catálise , Lactamas/química , Metano/química , Estrutura Molecular , Oxirredução , EstereoisomerismoRESUMO
An NHC-catalyzed formal [4 + 2] reaction of isatins with N-hydroxybenzotriazole ester of α,ß-unsaturated carboxylic acids bearing γ-H to construct spirocyclic oxindole-dihydropyranones featuring a chiral tetrasubstituted carbon stereogenic center was developed. The high enantioselectivity, the ready availability of the raw materials, the facile assembly, and the potential biological significance of the final products make this protocol an attractive alternative for the synthesis of spirocyclic heterocycles.
Assuntos
Ácidos Carboxílicos/química , Indóis/síntese química , Isatina/química , Pironas/síntese química , Compostos de Espiro/síntese química , Triazóis/química , Catálise , Ésteres , Compostos Heterocíclicos/química , Indóis/química , Metano/análogos & derivados , Metano/química , Estrutura Molecular , Pironas/química , Compostos de Espiro/química , EstereoisomerismoRESUMO
A NHC-catalyzed [4 + 2] cyclization of 2-bromo-2-enal bearing γ-H with 3-alkylenyloxindoles under mild reaction conditions gives spirocarbocyclic oxindoles containing one quaternary carbon in moderate to good yields with high diastereoselectivities. The easy availability of the starting materials, the concise assembly and the potential utilization value of the products make this strategy attractive in molecular biology and pharmacy.