RESUMO
Ti(IV)-salan 4 catalyzes the diastereo- and enantioselective monoepoxidation of conjugated dienes using 30% H2O2 at rt or below even in the presence of other olefins and adjacent stereocenters. Its enantiomer, ent-4, provides access to the opposite diastereomer or enantiomer. The resultant chiral allylic epoxides, and the triols derived from them, are versatile synthetic intermediates as well as substructures present in many bioactive natural products. The epoxidation is highly specific for Z-olefins. For 1-acyl(silyl)oxypenta-2,4-dienes, epoxidation of the distal olefin is generally favored in contrast to the adjacent regioselectivity characteristic of Sharpless, peracid, and other directed epoxidations of hydroxylated dienes.
Assuntos
Alcadienos/química , Compostos de Epóxi/síntese química , Alcadienos/síntese química , Produtos Biológicos/química , Catálise , Técnicas de Química Combinatória , Compostos de Epóxi/química , Peróxido de Hidrogênio/química , Estrutura Molecular , EstereoisomerismoRESUMO
Methyltrioxorhenium (MTO) complexed with pyridine was shown to be a highly effective catalyst for the regioselective monoepoxidation of conjugated di- and trienes using 30% H2O2 at or below room temperature. The resultant allylic epoxides, and the triols derived from them, are versatile synthetic intermediates as well as substructures present in many bioactive natural products. The site of epoxidation was dependent upon olefin substitution, olefin geometry (Z vs E), and the presence of electron-withdrawing substituents on adjacent carbons. For 1-acyl(silyl)oxypenta-2,4-dienes, epoxidation of the distal olefin was generally favored in contrast to the adjacent regioselectivity characteristic of Sharpless, peracid, and other directed epoxidations of hydroxylated dienes.
Assuntos
Alcenos/química , Compostos de Epóxi/síntese química , Peróxido de Hidrogênio/química , Compostos Organometálicos/química , Catálise , Compostos de Epóxi/química , Estrutura Molecular , EstereoisomerismoRESUMO
The synthesis of stilbenoids and styryl carboxylic acids is accomplished with high E-stereoselectivity by olefination of aldehydes with thiophthalides under basic conditions. The olefination is highly atom-efficient as it only loses elemental sulfur during the reaction. This olefination, in conjunction with retro Kolbe-Schmitt reaction, allows facile synthesis of E-hydroxystilbenoids with minimal employment of protecting groups. This study also discloses two important findings: formation of i) 4-methylsulfanyl isocoumarins and ii) an 2-arylindenone.
Assuntos
Benzofuranos/química , Estilbenos/química , Estirenos/síntese química , Compostos de Sulfidrila/química , Aldeídos/química , Alcenos/química , Hidroxilação , Modelos Moleculares , Estrutura Molecular , EstereoisomerismoRESUMO
The first total synthesis of euplectin, a rare metabolite with a chromone annulated indenone motif, has been accomplished in 17 steps. This has been possible through interplay among three key reactions: a Hauser sulfoxide annulation, a new chromone formation and a late-stage retro-Diels-Alder reaction. The entire regiochemical integrity of the successful route is established by an iodine-catalyzed aromatization of a cyclohexane-1,3-dione and the Hauser annulation.