Asymmetric Pauson-Khand reactions using camphor-derived chelating thiols as chiral controllers.
A convenient procedure for the preparation of enantiopure 10-(R-thio)-2-exo-bornanethiols from (1S)-camphor-10-thiol has been developed. The ethynyl derivatives of these thiols gave excellent diastereoselectivities (up to 98:2) in Pauson-Khand reactions with norbornene and norbornadiene through the intermediacy of a chelated dicobalt pentacarbonyl complex. Thermal reaction conditions starting from the preformed chelated complex gave better results than N-oxide-promoted runs with in situ generation of the chelated intermediate. The corresponding adducts have been elaborated through a protocol consisting of conjugate addition, samarium iodide-promoted cleavage of the chiral auxiliary, and retro-Diels-Alder reaction to afford 4-substituted 2-cyclopentenones in high enantiomeric purity.
Marchueta
I
I
Unitat de Recerca en Síntesi Asimètrica, Departament de Química Orgànica, Universitat de Barcelona, Martí i Franqués 1-11, 08028 Barcelona, Spain.
Montenegro
E
E
Panov
D
D
Poch
M
M
Verdaguer
X
X
Moyano
A
A
Pericàs
M A
MA
Riera
A
A