posted on 1998-03-06, 00:00authored byRosa L. Dorta, Angeles Martín, José A. Salazar, Ernesto Suárez, Thierry Prangé
The syntheses of trioxadispiroacetals from
carbohydrates are described.
(5R,7S,13R)-13-Methoxy-1,6,8-trioxadispiro[4.1.5.3]pentadecane (23) and
(5S,7S,13R)-13-methoxy-1,6,8-trioxadispiro[4.1.5.3]pentadecane (24) were prepared starting from
d-galactose. The construction of the
lateral
tetrahydrofuran and tetrahydropyran rings was realized by homologation
at C1 and C6 by
appropriate tethers possessing a terminal primary alcohol. The
cyclization of these alcohols at C1
and C5, respectively, was performed with
(diacetoxyiodo)benzene and iodine in order to
generate
the alkoxy radicals which undergo an intramolecular hydrogen
abstraction reaction. The diastereoisomers
(5R,7S,13S)-13-methoxy-1,6,8-trioxadispiro[4.1.5.3]pentadecane
(37) and
(5S,7S,13S)-13-methoxy-1,6,8-trioxadispiro[4.1.5.3]pentadecane
(38) were prepared starting from
tri-O-acetyl-d-glucal using a suitable methodology in which homologation
and intramolecular hydrogen
abstraction were again the key steps. We believe that this
protocol could be easily extended to
other tricyclic dispiroacetal ring systems.