Enantioselective Synthesis of Spiro Ethers and Spiro Ketals via Photoaddition of Dihydro-4-pyrones to Chiral 1,3-Dioxin-4-ones

Strategies for the synthesis of furo-pyranones and their application in the total synthesis of related natural products

The furo-pyranone framework is widely present in the molecular structure of various biologically potent natural products and un-natural small molecules, and it represents a valuable target in synthetic organic chemistry and medicinal chemistry.

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.

Thermolysis of 1,3-dioxin-4-ones: fast generation of kinetic data using in-line analysis under flow

Rapid acquisition of kinetic data for thermolysis of 1,3-dioxin-4-ones is demonstrated with a commercial meso-scale flow reactor, using a step-change in flow rate or ‘push-out’ from the flow line.

Dioxanone-fused dienes enable highly endo-selective intramolecular Diels-Alder reactions

Intramolecular Diels-Alder reactions of dioxanone-fused (Z,Z)-dienes, available in a stereoselective manner from the corresponding alcohols are described. These dienes exhibited high reactivity and high levels of endo selectivity, giving functionalized trans-fused bicyclic compounds.

Enantioselective synthesis of 3,4-dihydro-1,2-oxazepin-5(2H)-ones and 2,3-dihydropyridin-4(1H)-ones from β-substituted β-hydroxyaminoaldehydes

The synthesis of 3,4-dihydro-1,2-oxazepin-5(2H)-ones and 2,3-dihydropyridin-4(1H)-ones from β-substituted β-hydroxyaminoaldehydes is reported. The β-hydroxyaminoaldehydes were prepared by enantioselective organocatalytic 1,4-addition of N-tert-butyl (tert-butyldimethylsilyl)oxycarbamate to α,β-unsaturated aldehydes (MacMillan protocol). Alkyne addition to the aldehydes followed by alcohol oxidation furnished N-Boc O-TBS-protected β-aminoynones. Removal of the TBS protecting group initiated a 7-endo-dig cyclization to yield previously unknown 3,4-dihydro-1,2-oxazepin-5(2H)-ones. Reductive cleavage of the N-O bond of the oxazepinones and Boc-deprotection provided 2-substituted 2,3-dihydropyridin-4(1H)-ones via 6-endo-trig cyclization. 2,3-Dihydropyridin-4(1H)-ones are versatile intermediates that have been used for the synthesis of many alkaloids. The new protocol allows the synthesis of 3-dihydropyridin-4(1H)-ones carrying an array of substituents at C2 that cannot be prepared from commercial β-amino acids or by one-carbon homologation of proteinogenic amino acids. The use of readily available β-hydroxylaminoaldehydes expands the utility of our previously reported method to prepare 2,3-dihydropyridin-4(1H)-ones from β-amino acids as the source of diversity and chirality. A broad substrate scope is possible because β-aminoaldehydes can be prepared from α,β-unsaturated aldehydes by an enantioselective organocatalytic process.

Direct syntheses of spiro- and fused-hydrofurans by a tunable tandem semipinacol rearrangement/oxa-Michael addition protocol

A highly chemoselective one-pot reaction has been developed involving a tandem semipinacol rearrangement/oxa-Michael addition sequence in which the in situ generated ketol diene intermediate can be transformed specifically to either the spiro- or fused-dihydrofuran products (see scheme). This one-pot tandem reaction represents a general synthetic methodology for the syntheses of the two different kinds of furan derivatives.

Stereoselective synthesis of sugar fused β-disubstituted γ-butyro-lactones: C-spiro-glycosides from 1,2-cyclopropanecarboxylated sugars

A stereoselective methodology was developed for the construction of C-spiro-glycosides in two steps involving bromonium ion activated solvolytic ring opening of sugar derived 1,2-cyclopropanecarboxylates followed by a one-pot dehydrohalogenation, intramolecular hetero-Michael addition (IHMA) and ester hydrolysis. The obtained spirocyclic lactols were further converted to enantiomerically pure spirolactones.

Pyrone and pyridone compounds in the liquid culture of Physisporinus sanguinolentus

Chromatographic separation of the liquid culture filtrate of the basidiomycete fungus Physisporinus sanguinolentus has yielded three new compounds viz., 2-methyl-4-pyrone, 2-methyl-5,6-dihydro-4-pyrone and the pyridone form of 4-hydroxy-2-methylpyridine, together with the known triacetic acid lactone, the sesquiterpene dialdehyde merulidial and a derivative of merulidial. Their structures were elucidated by spectroscopic analysis and by comparison to literature data and a synthetic sample. One of the compounds, merulidial, was shown to inhibit the germination of spores and the hyphal growth of the wood-rotting basidiomycete Heterobasidion annosum and the saprophytic mould Cladosporium cucumerinum.