Diastereoselective Cycloadditions of Nitroalkenes as an Approach to the Assembly of Bicyclic Nitrogen Heterocycles.
A three-component coupling for the rapid assembly of nitrogenated bicycles has been developed that employs the sequential cycloaddition of nitroalkenes as 4pi components and both an electron-rich vinyl ether and electron-withdrawing alkenes. Given the distinct electronic character of nitroalkenes and the intermediate nitronates, the coupling represents an atom-economy strategy without side products resulting from competitive reactions. Either with a racemic nitroalkene or an enantiopure nitroalkenyl sugar, these processes were regiospecific leading to the formation of bicyclic nitrosoacetals with high facial diastereoselectivity. The stereochemistry of the cycloadducts was assigned by NMR spectroscopic techniques, and those of 2 and 15 were corroborated by X-ray crystallographic analysis. The unmasking of the nitrosoacetal moiety under mild conditions represents a homologation route for higher aldehydo sugars.
Avalos
Martín
M
Departamento de Química Orgánica, Facultad de Ciencias, Universidad de Extremadura, E-06071 Badajoz, Spain.
Babiano
Reyes
R
Cintas
Pedro
P
Higes
Francisco J.
FJ
Jiménez
José L.
JL
Palacios
Juan C.
JC
Silva
María A.
MA