RESUMO
We report a highly stereoselective synthesis of all-carbon or fluorinated tetrasubstituted alkenes from diazo reagents and fluorinated enol silyl ethers, using C-F bond as a synthetic handle. Cationic AuI catalysis plays a key role in this reaction. Remarkable fluorine effects on the reactivity and selectivity was also observed.
RESUMO
We report an efficient Mukaiyama-aldol reaction of tryptanthrin with fluorinated enol silyl ethers, which is carried out in methanol without the use of any catalyst. This method is applied to the total synthesis of the difluoro analogues of the natural product Phaitanthrin B.
Assuntos
Aldeídos/química , Química Orgânica/métodos , Éteres/química , Halogenação , Quinazolinas/química , Silanos/síntese química , Produtos Biológicos/síntese química , Produtos Biológicos/química , Catálise , Espectroscopia de Ressonância Magnética , Silanos/químicaRESUMO
A chiral secondary amine phosphoramide was developed and identified as a powerful catalyst for the Mukaiyama-Michael addition of fluorinated enol silyl ethers to tetrasubstituted olefins. The resulting products are obtained with high enantioselectivities and contain a quaternary carbon stereocenter bearing either a difluoroalkyl or monofluoroalkyl group.
RESUMO
A rare example of a one-pot process that involves asymmetric triple relay catalysis is reported. The key step is an asymmetric [1,5] electrocyclic reaction of functionalized ketimines. The substrates for this process were obtained inâ situ in a two-step process that involved the hydrogenation of nitroarenes with a Pd/C catalyst to yield aryl amines and their subsequent coupling with isatin derivatives in a Brønsted acid catalyzed ketimine formation reaction. The electrocyclization was catalyzed by a bifunctional chiral Brønsted base/hydrogen bond donor catalyst. The one-pot process gave the desired products in good yields and with excellent enantioselectivity.
RESUMO
We report a general and highly efficient Mukaiyama-aldol reaction of ketones and difluoroenoxysilanes. While the reaction of aryl ketones worked efficiently in the presence of Bi(OTf)3, that of aliphatic ketones required the use of Sc(OTf)3. In addition, Sc(OTf)3 was capable of achieving excellent 1,2-selectivity in the corresponding reaction of α,ß-unsaturated ketones. This method provides a facile access to differently substituted ß-hydroxy α,α-difluoro ketones, versatile synthons for difluomethylated tertiary alcohols.