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.National Institute of General Medical Sciences (U.S.) (GM72566)National Institute of General Medical Sciences (U.S.) (F32GM095014

Rhodium-catalyzed epoxide-opening cascades toward brevisin and hemibrevetoxin B

Thesis: Ph. D., Massachusetts Institute of Technology, Department of Chemistry, 2014.Cataloged from PDF version of thesis. Vita.Includes bibliographical references.CHAPTER I. Rhodium-Catalyzed Epoxide-Opening Cascades: Formal Synthesis of (-)-Brevisin [chemical formula inserted] [Rh(CO)₂Cl]₂ was found to be an effective catalyst for endo-selective cyclizations and cascades of epoxy-(E)-enoate alcohols, thus enabling the synthesis of oxepanes and oxepanecontaining 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 CHAPTER II. Synthetic Studies Toward Hemibrevetoxin B [chemical formula inserted] We report progress toward a biomimetic epoxide-opening cascade of the marine ladder polyether hemibrevetoxin B. Model studies demonstrate the ability of both [Rh(CO)₂Cl]₂ and cationic Rh(I) species to override the typical exo-directing of proximal methyl groups on in epoxy alcohol cyclizations for the synthesis of oxepanes. The synthesis of tri-epoxide cascade precursor and initial investigations toward an epoxide-opening cascade are described as well.by Kurt W. Armbrust.Ph. D

Rhodium-Catalyzed <i>Endo</i>-Selective Epoxide-Opening Cascades: Formal Synthesis of (−)-Brevisin

[Rh­(CO)₂Cl]₂ is as an effective catalyst for <i>endo</i>-selective cyclizations and cascades of epoxy-(<i>E</i>)-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 <i>endo</i>-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

Quaternary Charge-Transfer Complex Enables Photoenzymatic In-termolecular Hydroalkylation of Olefins

Intermolecular C–C bond-forming reactions are underdeveloped transformations in the field of biocatalysis. Here we report a photoenzymatic intermolecular hydroalkylation of olefins catalyzed by flavin-dependent ‘ene’reductases. Radical initiation occurs via photoexcitation of a rare high-order enzyme-templated charge-transfer complex that forms between an alkene, -chloroamide, and flavin hydroquinone. This unique mechanism ensures that radical formation only occurs when both substrates are present within the protein active site. This active site can control the radical terminating hydrogen atom transfer, enabling the synthesis of enantioenriched γ-stereogenic amides. This work highlights the potential for photoenzymatic catalysis to enable new biocatalytic transformations via previously unknown electron transfer mechanisms

Quaternary Charge-Transfer Complex Enables Photoenzymatic Intermolecular Hydroalkylation of Olefins.

Intermolecular C-C bond-forming reactions are underdeveloped transformations in the field of biocatalysis. Here we report a photoenzymatic intermolecular hydroalkylation of olefins catalyzed by flavin-dependent 'ene'-reductases. Radical initiation occurs via photoexcitation of a rare high-order enzyme-templated charge-transfer complex that forms between an alkene, α-chloroamide, and flavin hydroquinone. This unique mechanism ensures that radical formation only occurs when both substrates are present within the protein active site. This active site can control the radical terminating hydrogen atom transfer, enabling the synthesis of enantioenriched γ-stereogenic amides. This work highlights the potential for photoenzymatic catalysis to enable new biocatalytic transformations via previously unknown electron transfer mechanisms