RESUMO
The vinylogous Mukaiyama aldol reaction (VMAR) of chiral nonracemic ketene silyl N,O-acetal with various aldehydes is demonstrated. VMAR with alpha-heteroatom-unsubstituted aldehydes proceeded with a high degree of anti-selectivity. In sharp contrast, moderate to high syn-selectivity was observed when alpha-heteroatom-substituted aldehydes were used.
Assuntos
Aldeídos/química , Oxazóis/química , Alcenos/síntese química , Alcenos/química , Técnicas de Química Combinatória , Estrutura Molecular , Oxazóis/síntese química , Silanos/química , EstereoisomerismoRESUMO
[structure: see text] A convergent total synthesis of khafrefungin was accomplished on the basis of (1) the highly stereoselective TiCl4-mediated vinylogous Mukaiyama aldol reaction using vinylketene silyl N,O-acetal and (2) syn-selective aldol reaction of enal 5a and ethyl ketone 6 followed by anti-dehydration under Mitsunobu conditions.
Assuntos
Glicolipídeos/síntese química , Glicolipídeos/química , Estrutura Molecular , EstereoisomerismoRESUMO
[reaction: see text] The first enantioselective total synthesis of convolutamydines B and E has been achieved using our vinylogous Mukaiyama aldol reaction. The synthesis features highly diastereoselective vinylogous Mukaiyama aldol reaction with isatin instead of aldehydes to construct a chiral center of convolutamydines. Additionally, the absolute configuration of natural convolutamydine B has been determined as R by its CD spectrum.
Assuntos
Alcaloides Indólicos/síntese química , Isatina/análogos & derivados , Isatina/síntese química , Animais , Briozoários/química , Catálise , Dicroísmo Circular , Alcaloides Indólicos/química , Isatina/química , Estrutura MolecularRESUMO
A highly regio- and diastereoselective TiCl4-mediated vinylogous Mukaiyama aldol reaction using the chiral vinylketene silyl N,O-acetal has been developed. The present vinylogous Mukaiyama aldol reaction provides a unique and effective means of controlling remote asymmetric induction. The methyl group at the alpha-position is important in achieving a high level of stereoselectivity. From a synthetic point of view, this methodology can provide a one-step construction of delta-hydroxy-alpha,gamma-dimethyl-alpha,beta-unsaturated carbonyl unit that is seen in many natural polyketide products.
