Endo-selective intramolecular Pauson-Khand reactions of gamma-oxygenated-alpha,beta-unsaturated phenylsulfones.
A wide variety of 1,6-enynes and 1,7-enynes incorporating gamma-oxygenated-alpha,beta-unsaturated phenylsulfone moieties have readily been prepared by piperidine-promoted condensation of the corresponding alkynyl aldehyde with phenylsulfonyl-(p-tolylsulfinyl)methane and further protection of the hydroxyl group. Despite the enduring claim concerning the unsuitability of electronically deficient olefins in Pauson-Khand reactions, we report that these 1-sulfonylated enynes are excellent substrates in intramolecular Pauson-Khand reactions under both thermal and amine N-oxide-promoted conditions. Moreover, in contrast with the usual exo-selective Pauson-Khand cyclization of allylic substituted enynes, the reactions of these 1-sulfonylated-3-oxygenated enynes occur with a moderate or high endo selectivity. The evaluation of the chemical and stereochemical scope of the process in comparison with the Pauson-Khand cyclization of non-sulfonylated enynes, its application to the stereoselective preparation of optically pure C6-substituted bicyclo[3.3.0]oct-1-en-3-ones, and the interpretation of the stereochemical outcome are also discussed.
Adrio
J
J
Departamento de Química Orgánica, Facultad de Ciencias, Universidad Autónoma de Madrid, Spain.
Rodríguez Rivero
M
M
Carretero
J C
JC