Oxidative spirocyclisation routes towards the sawaranospirolides. Synthesis of ent-sawaranospirolides C and D

Synthesis of the MN Ring of Caribbean Ciguatoxin C-CTX-1 via Desymmetrization by Acetal Formation

The MN ring of Caribbean ciguatoxin C-CTX-1 was synthesized from a meso-syn-2,7-dimethyloxepane derivative corresponding to the M ring via desymmetrization by acetal formation with a camphor derivative, followed by construction of the N ring via the Horner-Wadsworth-Emmons reaction and acetal formation. The meso-syn-2,7-dimethyloxepane derivative was synthesized via photoinduced electrocyclization of a conjugated exo-diene under flow conditions, giving a cyclobutene derivative, followed by ring expansion via oxidative cleavage and diastereoselective reduction of a β-hydroxy ketone.

Palladium-Catalyzed Hydrocarbonylative Spirolactonization for Expedite Construction of Oxaspirolactones

A novel palladium-catalyzed cascade hydrocarbonylation of the alkene moiety followed by intramolecular spirolactonization of 2-vinylaryl hydroxyalkyl ketones has been developed, which offers efficient and expedited access to furnishing oxaspirolactones in high yields with high chemoselectivities. This new method is compatible with an array of functional groups and proceeds under mild reaction conditions with commercially available catalyst components.

Diels-Alder Reactions of 1-Alkoxy-1-amino-1,3-butadienes: Direct Synthesis of 6-Substituted and 6,6-Disubstituted 2-Cyclohexenones and 6-Substituted 5,6-Dihydropyran-2-ones

We report the cycloaddition reactions of 1-alkoxy-1-amino-1,3-butadienes. These doubly activated dienes are prepared on a multigram scale from crotonic acid chloride and its derivatives. The dienes undergo Diels-Alder (DA) and hetero-Diels-Alder (HDA) reactions under mild reaction conditions with a variety of electron-deficient dienophiles to afford cycloadducts in good yields with excellent regioselectivities. The hydrolysis of the DA cycloadducts provides 6-substituted and 6,6-disubstituted 2-cylohexenones, which are versatile building blocks for complex molecule synthesis. The corresponding HDA cycloadducts afford 6-substituted 5,6-dihydropyran-2-ones.

Recent advances in the synthesis of oxaspirolactones and their application in the total synthesis of related natural products

Oxaspirolactones are ubiquitous structural motifs found in natural products and synthetic molecules with a diverse biochemical and physicochemical profile, and represent a valuable target in natural product chemistry and medicinal chemistry.

Family-level stereoselective synthesis and biological evaluation of pyrrolomorpholine spiroketal natural product antioxidants

The pyranose spiroketal natural products pollenopyrroside A and shensongine A (also known as xylapyrroside A, ent-capparisine B) have been synthesized by stereoselective spirocyclizations of a common C1-functionalized glycal precursor. In conjunction with our previously reported syntheses of the corresponding furanose isomers, this provides a versatile family-level synthesis of the pyrrolomorpholine spiroketal natural products and analogues. In rat mesangial cells, hyperglycemia-induced production of reactive oxygen species, which is implicated in diabetic nephropathy, was inhibited by pollenopyrroside A and shensongine A with mid-μM IC50 values, while unnatural C2-hydroxy analogues exhibited more potent, sub-μM activity.

Catalytic Carbonylative Spirolactonization of Hydroxycyclopropanols

A palladium-catalyzed cascade carbonylative spirolactonization of hydroxycyclopropanols has been developed to efficiently synthesize oxaspirolactones common to many complex natural products of important therapeutic value. The mild reaction conditions, high atom economy, broad substrate scope, and scalability of this new method were highlighted in expedient total syntheses of the Turkish tobacco natural products α-levantanolide and α-levantenolide in two and four steps, respectively. The hydroxycyclopropanol substrates are readily available in one step via a Kulinkovich reaction of the corresponding lactones. Mechanistic studies utilizing high-resolution electrospray ionization mass spectrometry (ESI-MS) identified several key intermediates in the catalytic cycle, as well as those related to catalyst decomposition and competitive pathways.

Stereoselective synthesis of 1,6-dioxaspirolactones from spiro-cyclopropanecarboxylated sugars: total synthesis of dihydro-pyrenolide D

A one-pot protocol for the stereoselective construction of γ-spiroketal γ-lactone frameworks from sugar derived spiro-cyclopropanecarboxylic acids involving a ring enlargement and cyclization reaction is revealed.