Abstract
Conjugate addition of α-nitrosulfones to vinyl ketones in the presence of 0.2 mol% of a quinine-squaramide organocatalyst afforded α-nitro-δ-ketosulfones possessing a tetrasubstituted chiral center in excellent yield and enantioselectivity in most cases. This strategy also offers a facile and convenient entry into γ-sulfonylhydroxamates that are one carbon homologs of potent enzyme inhibitors.
Highlights
Conjugate addition of a-nitrosulfones to vinyl ketones in the presence of 0.2 mol% of a quinine–squaramide organocatalyst afforded a-nitrod-ketosulfones possessing a tetrasubstituted chiral center in excellent yield and enantioselectivity in most cases
B-sulfonylhydroxamate 1a, in which a sulfonyl group is attached to a chiral center, is a potent matrix metalloprotease (MMP) and PDE inhibitor (Fig. 1).[2,3]
The enantiopure compound 1a displays superior activity as compared to the racemic one and the enantioselective synthesis of 1a involves the oxidation of an enantioenriched thioether precursor.[3]
Summary
Conjugate addition of a-nitrosulfones to vinyl ketones in the presence of 0.2 mol% of a quinine–squaramide organocatalyst afforded a-nitrod-ketosulfones possessing a tetrasubstituted chiral center in excellent yield and enantioselectivity in most cases. The reaction conditions were optimized by performing Michael addition of nitrosulfone 3a to phenyl vinyl ketone 2a using several cinchona-based bifunctional organocatalysts and solvents at different temperatures (Fig. 2 and Table 1). The Michael adduct 4a, a quaternary a-nitrosulfone, was isolated in good yield (96%) and enantioselectivity (90% ee) when 10 mol% of C1 was employed in mesitylene at rt (entry 1).
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