RESUMO
A novel, organobase-catalyzed and highly chemoselective Michael-Michael-acetalization cascade is presented for the efficient synthesis of spiro-indandione skeletons. Following this very simple protocol, a broad range of products was obtained in good yields with excellent diastereocontrol. The role of steric factors in the acetalization step was evaluated.
RESUMO
A Bu3P-mediated cyclization reaction of 3-cinnamoyl-4-hydroxy-2H-chromen-2-ones though electrophilic addition of acyl chlorides towards the synthesis of highly functionalized furo[3,2-c]coumarins bearing a phosphorus ylide moiety is described. These unprecedented cyclization reaction proceeds under mild reaction conditions within short reaction times (1â min to 1â h), and can be further applied in the synthesis of alkenyl-substituted furo[3,2-c]coumarins by the treatment with carbonyl electrophiles under basic conditions.
Assuntos
Cloretos/química , Cromonas/química , Furocumarinas/síntese química , Acilação , Catálise , Cloretos/síntese química , Cromonas/síntese química , Ciclização , Furocumarinas/químicaRESUMO
This publication describes a highly selective oxidation of aldehydes to the corresponding acids or esters. The reaction proceeds under metal-free conditions by using N-heterocyclic carbenes as organocatalysts in combination with environmentally friendly oxygen as the terminal oxidation agent.
RESUMO
The Au(I) atom in the title compound, [Au(C(21)H(24)N(2))(2)](C(24)H(20)B(5)O(6)), adopts a slightly distorted linear AuC(2) coordination geometry arising from its coordination by two mesitylenic N-heterocyclic carbene ligands, forming an overall cationic complex. The dihedral angle between the imidazole rings is 57.3â (6)°. In the crystal, the components are linked by weak C-Hâ¯O hydrogen bonds.
RESUMO
An unprecedented organocatalytic enantioselective vinylogous Michael addition/Henry cyclization cascade is presented for the synthesis of highly substituted tetrahydrofluoren-9-ones 3 employing novel 1,3-indandione-derived pronucleophiles 1a-g and nitroalkenes 2. Following a very simple protocol, a wide range of products were obtained in good to excellent yields and with excellent enantioinduction (43-98% yield, up to 98% ee). The reaction proceeded with excellent diastereocontrol despite the simultaneous generation of four stereogenic centers. Surprisingly, when 2-(1-phenylethylidene)-1H-indandione (1h) was used as a pronucleophile, no cyclization was observed, and only Michael addition adducts 4a-x were furnished in very good yields and excellent enantioselectivities.