Total Synthesis of Pentaketide Ansamycin Microansamycin H

Herein, we report the first total synthesis of pentaketide ansamycin microansamycin H. Key to our success was the endo-selective epoxide-opening O-alkylation to construct the elusive seven-membered benzoxepane core. Due to the electron-rich disposition of the aromatic substrate, our pivotal transformation was hindered by competing electrophilic aromatic substitution at multiple C-based nucleophilic sites that generated kinetically favored products. Judicious choices of transition metal Lewis acid promoters biased toward the formation of the desired oxepane.

Palladium-catalysed regio- and stereoselective arylative substitution of γ,δ-epoxy-α,β-unsaturated esters and amides by sodium tetraaryl borates

The palladium-catalysed reaction of γ,δ-epoxy-α,β-unsaturated esters or amides with NaBAr₄reagents proceeded regio- and stereoselectively to produce aryl-substituted homoallyl alcohols.

Synthesis of Phostones via the Palladium-Catalyzed Ring Opening of Epoxy Vinyl Phosphonates

The reaction of epoxy aldehydes with tetraethyl methylenediphosphonate gave γ,δ-epoxy vinyl phosphonates. The palladium-catalyzed addition of primary alcohols gave the monoprotected diols as single diastereoisomers. The trans- and cis-epoxides lead to opposite ( syn and anti) diastereoisomers of the addition products. The alkene of the vinyl phosphonates was subjected to hydrogenation, and the resulting saturated phosphonates underwent base-catalyzed cyclization to give phostones with a very high diastereoselectivity in the formation of the new chiral center at the phosphorus atom.

Rhodium-catalyzed endo-selective epoxide-opening cascades: formal synthesis of (-)-brevisin

[Rh(CO)2Cl]2 is as an effective catalyst for endo-selective cyclizations and cascades of epoxy-(E)-enoate alcohols, thus enabling the synthesis of oxepanes and oxepane-containing polyethers from di- and trisubstituted epoxides. Syntheses of the ABC and EF ring systems of (-)-brevisin via all endo-diepoxide-opening cascades using this method constitute a formal total synthesis and demonstrate the utility of this methodology in the context of the synthesis of marine ladder polyether natural products.