Synthesis of β,γ-Dihydroxyhomotyrosines by a Tandem Petasis–Asymmetric Dihydroxylation Approach

Petasis reactions of substituted styrenylboronic acids and glyoxylic acid, employing tert-butylsulfinamide as the 'amine' component, proceed with high stereoselectivity to produce β,γ-dehydrohomoarylalanine derivatives. Subsequent asymmetric dihydroxylation under neutral conditions gives the corresponding protected β,γ-dihydroxyhomoarylalanines with up to 15:1 dr. The method has been exploited in the efficient, stereoselective synthesis of protected β,γ-dihydroxyhomotyrosine, a component of the antifungal cyclic peptide echinocandin B.