Search

We have recently disclosed a palladium-catalyzed Trost- Oppolzer type Alder-ene reaction of 2,4-pentadienyl acetates for the synthesis of highly substituted cyclopentadienes and cyclopentenefused aromatics. The overall transformation also represents an acid-free iso-Nazarov type cyclization. Herein, we provide the hypothesis and rationale behind this work, while highlighting the seminal contributions of Trost, Oppolzer and others towards the development of the palladium- ene reaction. [ABSTRACT FROM AUTHOR]

Abstract: A new approach to the synthesis of highly substituted cyclopentadienes, indenes, and cyclopentene‐fused heteroarenes by means of the Pd‐catalyzed Trost–Oppolzer‐type intramolecular Alder–ene reaction of 2,4‐pentadienyl acetates is described. This unprecedented transformation combines the electrophilic features of the Tsuji–Trost reaction with the nucleophilic features of the Alder–ene reaction. The overall outcome can be perceived as a hitherto unknown “acid‐free” iso‐Nazarov‐type cyclization. The versatility of this strategy was further demonstrated by the formal synthesis of paucifloral F, a resveratrol‐based natural product. [ABSTRACT FROM AUTHOR]

An unusual and facile approach for the synthesis of 2-benzofuranyl-3-hydroxyacetones from 6-acetoxy-β-pyrones and phenols is presented. The synthetic sequence involves a cascade transacetalisation, Fries-type O → C rearrangement followed by Michael addition and ring-opening aromatisation. The versatility of this method was further demonstrated via the synthesis of 4,4a-dihydropyrano[3,2-b]benzofuran-3-ones, furo[3,2-c]coumarins, and spiro[benzofuran-2,2′-furan]-4′-ones. The unexpected cascade event would also provide new possible considerations in the β-pyrone-involved organic synthesis. [ABSTRACT FROM AUTHOR]

An efficient diversity-oriented approach for the synthesis of previously unknown di-, tri-, tetra- and spirocyclic pyrano-1,4-dioxinones, pyrano-1,4-dithiinones and pyrano-1,4-oxathiinones from readily available starting compounds has been described. Cascade Michael addition-cycloacetalisation of acetoxy-, alkoxy-, and aryloxypyranones and 1,2-dinucleophiles under mild Lewis acidic conditions provides a direct access to oxygen and sulfur-containing complex heterocycles. Mechanistic aspects of the cascade process were elucidated in light of experimental facts. The methodology described herein shows high promise for the synthesis of several bioactive natural products as well as pharmaceutically important compounds. [ABSTRACT FROM AUTHOR]

A facileapproach for the synthesis of furopyrans and bicyclicbisacetals under mild aqueous conditions is described. This potentiallygreen, diversity oriented approach involves cascade Michael additionand cycloacetalization of pyranones and 1,3-dicarbonyls. An interestingswitch in the product class was observed depending on the type ofpyranone employed. Products of type Iand IIobtained herein are an integral part of several bioactive naturalproducts and medicinally interesting compounds. [ABSTRACT FROM AUTHOR]

An abstract of the article "Synthesis of Benzofurans via an Acid Catalyzed Transacetalization/Fries-Type O-C Rearrangement/Michael Addition/Ring-Opening Aromatization Cascade of B2-Pyrones," by Siddheshwar K. Bankar and colleagues is presented.

A diagram is presented which shows the synthesis of polycycles through one-pot Michael addition, a cycloacetalization cascade.

Acetoxypyranones (I) and (VIII) undergo cascade Michael addition and cycloacetalization to afford furopyrans. [ABSTRACT FROM AUTHOR]