Sequential Norrish typeâ
II photoelimination and intramolecular aldol cyclization of α-diketones: synthesis of polyhydroxylated cyclopentitols by ring contraction of hexopyranose carbohydrate derivatives.
Chemistry
; 19(31): 10312-33, 2013 Jul 29.
Article
em En
| MEDLINE
| ID: mdl-23788424
ABSTRACT
The excitation of the innermost carbonyl of nono-2,3-diulose derivatives by irradiation with visible-light initiates a sequential Norrish typeâ
II photoelimination and aldol cyclization process that finally gives polyfunctionalized cyclopentitols. The rearrangement has been confirmed by the isolation of stable acyclic photoenol intermediates that can be independently cyclized by a thermal 5-(enolexo)-exo-trig uncatalyzed aldol reaction with high diastereoselectivity. In this last step, the large deuterium kinetic isotope effect found for the 1,5-hydrogen atom transfer seems to indicate that the aldol reaction runs through a concerted pericyclic mechanism. Owing to the ready availability of pyranose sugars of various configurations, this protocol has been used to study the influence of pyranose ring-substituents on the diastereoselectivity of the aldol cyclization reaction. In contrast with other pyranose ring contraction methodologies no transition-metal reagents are needed and the sequential rearrangement occurs simply by using visible light and moderate heating (0 to 60 °C).
Palavras-chave
Texto completo:
1
Base de dados:
MEDLINE
Assunto principal:
Carboidratos
Idioma:
En
Revista:
Chemistry
Assunto da revista:
QUIMICA
Ano de publicação:
2013
Tipo de documento:
Article
País de afiliação:
Espanha