RESUMO
New organocatalysts have been developed for the enantioselective halolactonization of (Z)-1,3-enynes and 1,1-disubstituted alkenes. In the case of 1,3-enynes, the carboxylate nucleophile and halogen electrophile were added to the conjugated π-system from the same face. Up to 99% ee was achieved for the 1,4-syn-bromolactonization of conjugated (Z)-1,3-enynes. Based on the results from the enyne halolactonization, a second generation of catalysts was designed for simple olefins. Up to 91% ee was observed for chlorolactonization of 1,1-disubstituted alkenes. The catalysts developed for the enantioselective halolactonization of both enynes and alkenes are composed of a cinchona alkaloid skeleton tethered to a urea group.
Assuntos
Alcadienos/química , Alcinos/química , Bromo/química , Lactonas/química , Catálise , Técnicas de Química Combinatória , Ciclização , Modelos Químicos , Estrutura Molecular , EstereoisomerismoRESUMO
A stereoselective total synthesis of (-)-kumausallene was completed in 12 steps from acetylacetone. The hidden symmetry of (-)-kumausallene was recognized, and its skeleton was constructed efficiently from a C(2)-symmetric diol by a palladium-catalyzed cascade reaction. High diastereoselectivity was observed for the DMF-promoted biomimetic 1,4-bromocyclization of a conjugated enyne.
Assuntos
Paládio/química , Sesquiterpenos/síntese química , Catálise , Ciclização , Estrutura Molecular , Sesquiterpenos/química , EstereoisomerismoRESUMO
A catalytic enantioselective syn-1,4-bromolactonization of conjugated (Z)-enynes was reported. Diastereomeric ratios >20:1 and up to 99% enantiomeric excesses were observed. Di-, tri-, and tetra-substituted bromoallenes were prepared together with lactone heterocycles efficiently and stereoselectively. Preliminary investigations suggest that the chiral catalyst may serve as a bifunctional reagent by interacting with both a carboxylic acid nucleophile and NBS electrophile.
Assuntos
Alcinos/química , Bromo/química , Lactonas/química , Alcadienos/química , Catálise , Reagentes de Ligações Cruzadas/química , Compostos Heterocíclicos/química , Fenômenos Ópticos , Estereoisomerismo , Especificidade por SubstratoRESUMO
A de novo intramolecular hydroamination of conjugated enynes was developed using commercially available n-BuLi as a precatalyst. This hydroamination reaction successfully afforded allenyl-substituted pyrrolidines with up to 95% yield. One of the resulting allenyl pyrrolidines was converted to the natural products irniine and irnidine in three steps.
