Cyclic oxonium ylides: building blocks for iterative synthesis of polycyclic ethers

Accessing HIV-1 Protease Inhibitors through Visible-Light-Mediated Sequential Photocatalytic Decarboxylative Radical Conjugate Addition-Elimination-Oxa-Michael Reactions

A photocatalytic decarboxylative radical conjugate addition-elimination-oxa-Michael reaction of hydroxyalkylated carboxylic acids with cyclopentenones is developed to construct diverse cyclopentanonyl-fused functionalized 5-7 membered cyclic ethers. The stereoselective synthetic strategy is amenable to substructural variation, establishing a direct total synthetic route to two diastereomers of C3-amino cyclopentyltetrahydrofuranyl-derived potent HIV-1 protease inhibitors with low nanomolar IC₅₀ values.

Evidence for heterolytic cleavage of a cyclic oxonium ylide: implications for the mechanism of the Stevens [1,2]-shift

Formation and rearrangement of several oxonium ylides containing cyclopropylcarbinyl migrating groups were studied. Efficient ring-contraction by [1,2]-shift to form cyclopropane-substituted cyclobutanones was observed, with no competing cyclopropane fragmentation. Substitution with the hypersensitive mechanistic probe (trans,trans-2-methoxy-3-phenylcyclopropyl)methyl led to cyclopropane fragmentation via an apparent heterolytic pathway, providing the first evidence for ion pair intermediates from ylide cleavage, and suggesting a possible alternative heterolytic mechanism for the Stevens [1,2]-shift.

Rh-catalyzed intermolecular cyclopropanation with alpha-alkyl-alpha-diazoesters: catalyst-dependent chemo- and diastereoselectivity

A Rh-catalyzed procedure for the cyclopropanation of alkenes with alpha-alkyl-alpha-diazoesters is described. With dirhodium tetraoctanoate, the predominant pathway is beta-hydride elimination. While a number of sterically demanding carboxylate ligands serve to avoid beta-hydride elimination, it was found that triphenylacetate (TPA) also imparts high diastereoselectivity.

Convergent strategies for the total synthesis of polycyclic ether marine metabolites

Marine polycyclic ether natural products continue to fascinate chemists and biologists due to their exceptionally large and complex molecular architectures and potent and diverse biological activities. Tremendous progress has been made over the past decade toward the total synthesis of marine polycyclic ether natural products. In this area, a convergent strategy for assembling small fragments into an entire molecule always plays a key role in successful total synthesis. This review describes our efforts to develop convergent strategies for the synthesis of polycyclic ethers and their application to the total synthesis of gambierol, gymnocin-A, and brevenal, and to the partial synthesis of the central part of ciguatoxins and the nonacyclic polyether skeleton of gambieric acids.

[1,2]- or [2,3]-rearrangement of onium ylides of allyl and benzyl ethers and sulfides via in situ-generated iodonium ylides

Iodonium ylides, generated in situ with bisacetoxyiodobenzene, are converted to allyl- or benzyl-substituted oxonium or sulfonium ylides via rhodium- or copper-catalyzed carbene transfer. Except for the S-benzyl example, the resulting ylides undergo rearrangement to the corresponding 2-substituted heterocycles. This demonstrates the first use of iodonium ylides as diazoketone surrogates for the generation and rearrangement of onium ylide intermediates. This abbreviated one-step method proceeds in comparable yields relative to the corresponding two-step route employing diazoketone intermediates.

A Concise and Stereoselective Synthesis of the A-Ring Fragment of the Gambieric Acids

The A-ring fragment of the gambieric acids has been prepared by a short and efficient route. The key 3(2H)-furanone intermediate has been obtained by [2,3] rearrangement of an allylic oxonium ylide generated from intramolecular reaction of a crotyl ether with a copper carbenoid. A single stereogenic center has been set by using a chiral pool starting material and the other three have been established by using highly diastereoselective substrate-controlled transformations. [reaction--see text]

Allylation of Erythromycin Derivatives: Introduction of Allyl Substituents into Highly Hindered Alcohols

Functionalized erythromycin 9-oxime derivatives are 6-O-allylated under mild conditions using substituted allyl tert-butyl carbonates under palladium(0) catalysis. This allylation works well where traditional ether-forming protocols function poorly. Allyl tert-butyl carbonates provide higher yields in this reaction than lesser substituted carbonates such as ethyl or isopropyl. Aryl-substituted allyl carbonates or carbamates may be employed as well and, when used, produce trans-olefinic products.

Synthesis of an F-H gambierol subunit using a C-glycoside-centered strategy

[structure: see text] This manuscript describes our synthesis of the F-H subunit of gambierol. In addition to the synthesis of the tricycle, of note is an interesting protecting group influence on the generation of a C(23) C-glycoside as well as the use of ring-closing metathesis to generate a tetrasubstituted enol ether.