RESUMO
Polyketals are an important class of materials for drug delivery to sensitive tissues as they degrade in vivo to nonacidic species. We report the synthesis of high-molecular weight cyclic polyketals by the cationic ring-opening polymerization of bicyclic ketal monomers, which were prepared by the metal-catalyzed rearrangement of epoxy ketones. Three different cyclic polyketals with high molecular weights were synthesized using this protocol.
Assuntos
Compostos Bicíclicos Heterocíclicos com Pontes/química , Polimerização , Polímeros/química , Polímeros/síntese química , Técnicas de Química Sintética , Ciclização , Peso MolecularRESUMO
Two new catalysts are reported for the regioselective carbonylation of trans-disubstituted epoxides to cis-ß-lactones. The two catalysts display high and opposing selectivities, which generally are difficult to achieve for this class of epoxides. The resulting ß-lactones are well-defined precursors for a wide variety of aldol-type compounds. Altogether, carbonylation of disubstituted epoxides is established as a viable and economical entry into syn- and anti-aldol products.
RESUMO
The first psico-oxetanocin analogue of the powerful antiviral natural product, oxetanocin A, has been readily synthesized from cis-2-butene-1,4-diol. Key 2-methyleneoxetane precursors were derived from ß-lactones prepared by the carbonylation of epoxides. F(+)-mediated nucleobase incorporation provided the corresponding nucleosides in good yield but with low diastereoselectivity. Surprisingly, attempted exploitation of anchimeric assistance to increase the selectivity was not fruitful. A range of 2-methyleneoxetane and related 2-methylenetetrahydrofuran substrates was prepared to explore the basis for this. With one exception, these substrates also showed little stereoselectivity in nucleobase incorporation. Computational studies were undertaken to examine if neighboring group participation involving fused [4.2.0] or [4.3.0] intermediates is favorable.
Assuntos
Adenina/análogos & derivados , Antivirais/síntese química , Compostos de Epóxi/química , Éteres Cíclicos/química , Lactonas/química , Nucleosídeos/química , Adenina/síntese química , Butileno Glicóis/química , Flúor/química , Furanos/síntese química , Humanos , Espectroscopia de Ressonância Magnética , Estrutura Molecular , EstereoisomerismoRESUMO
4-Substituted oxazolines, which are readily synthesized from naturally occurring alpha-amino acids, are converted efficiently and stereospecifically to beta-amidoaldehydes in the presence of synthesis gas and catalytic dicobalt octacarbonyl.
