Alpha'-hydroxy enones as achiral templates for Lewis acid-catalyzed enantioselective Diels-Alder reactions.
alpha'-Hydroxy enones react with dienes in the presence of (S,S)-[Cu(tBu-box)](OTf)2 or (S,S)-[Cu(tBu-box)](SbF6)2 (2 to 10 mol %) to afford the corresponding Diels-Alder adducts in high yield and selectivity. Isomeric ratios (regioselectivity, endo/exo or cis/trans) of up to >99:1 and ee values of up to >99% are obtained. Significantly, difficult dienes such as isoprene, 2,3-dimethyl butadiene and piperylene behave satisfactorily. Subsequent oxidative cleavage of the ketol in the resulting cycloadducts by treatment with cerium ammonium nitrate (CAN) yields the corresponding enantiopure carboxylic acids. Alternatively, carbonyl addition and subsequent diol cleavage with CAN produces the corresponding ketone adducts.
Palomo
Claudio
C
Departamento de Química Orgánica I, Facultad de Química, Universidad del País Vasco, Apdo. 1072, 20080 San Sebastián, Spain. qoppanic@sc.edu.es
Oiarbide
Mikel
M
García
Jesús M
JM
González
Alberto
A
Arceo
Elena
E