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Chiral Amino Ether-Controlled Catalytic Enantioselective Arylthiol Conjugate Additions to α,β-Unsaturated Esters and Ketones: Scope, Structural Requirements, and Mechanistic Implications

2001; American Chemical Society; Volume: 67; Issue: 2 Linguagem: Inglês

10.1021/jo015879v

1520-6904

Katsumi Nishimura, Kiyoshi Tomioka,

Coordination Chemistry and Organometallics

Asymmetric conjugate addition reaction of 2-trimethylsilylbenzenethiol with enoates and enones is catalyzed by a chiral amino ether−lithium thiolate complex and affords adducts with high enantioselectivity. Both the s-cis conformation and a steric wall at one side of the carbonyl group are structural requirements in substrates yielding adducts with high enantioselectivity. Reactions with tert-butyl enones gave addition products with high enantioselectivity. Construction of two contiguous chiral centers was possible by this addition−protonation sequence. Methyl tiglate was stereoselectively converted to a single syn-adduct of 95% enantiomeric excess (ee) bearing two contiguous chiral centers. Methyl 2-phenyl-2-butenoate was converted to a single syn-adduct of 95% ee, which was desulfurized to methyl 2-phenylbutanoate of 95% ee. These additions generate a transient lithium enolate that is protonated by a thiol anti to the C−S bond, giving the corresponding product having two adjacent stereocenters.