The versatility of the ylide (triphenylphosphoranylidene)ketene (Ph 3 P=C=C=O, 3) in the construction of tetronic and tetramic acids from various carboxylic acid derivatives is demonstrated by new reactions and extensions of known ones. With a-hydroxy or a-amino esters, 3 affords tetronates or tetramates. A twostep synthesis of (-)-epi-blastmycinolactol shows that allyl a-hydroxy esters can be domino Wittig-Claisen reacted to give 3-allyltetronic acids. More extended Wittig-Claisen-Conia cascades can produce 3-alkylidenefuran-2,4-diones, the photooxygenation of which furnishes lactone endoperoxides with antiplasmodial potential. Tetronic acids can be acylated by 3 at C3 to give the corresponding acyl ylides. Their saponification yields the respective 3acetyl compounds, e.g. the fungal metabolite pesthetoxin. a-Hydroxy acids react with 3 to afford the corresponding 3-phosphoranylidenefuran-2,4-diones. The antibiotic (R)-reutericyclin was built up from benzyl D-leucinate and 3 in four steps by downstream acylation first at C3, then at N1 without racemization.

No abstract

: The five-member oxacyclic system of furan-2(5H)-ones, commonly named as γ-butenolides or properly as ∆α,β butenolides, is of high interest since many studies have proven its bioactivity. During past years, ∆α,β-butenolides have been important synthetic targets, with several reports of new procedures for their construction. A short compendium of these main different synthetic methodologies focused on the ∆α,β-butenolide ring formation, along with selected examples of compounds with relevant biological activities of these promising pharmaceutical entities is presented.

2005 Furan derivatives R 0060Annulated Butanolides by Ring Closing Metathesis of Diallyltetronic Acid Derivatives. -Two methods are described for the synthesis of 3,3-diallyldihydrofuran--2,4-diones such as (III) and (VIII). Their conversion to spirocyclic or bicyclic furan derivatives under Grubbs' ring closing metathesis conditions is demonstrated. -(SCHOBERT*, R.; URBINA-GONZALEZ, J. M.; Tetrahedron Lett. 46 (2005) 21, 3657-3660; Lab. Org. Chem., Univ. Bayreuth, D-95440 Bayreuth, Germany; Eng.) -Mais 37-108

Los grupos protectores alilo y bencilo fueron facilmente adicionados sobre una serie de ácidos (ciclo)alquil α-hidroxicarboxílicos mediante una modificación a la esterificación de Steglich, utilizando O-alil y O-bencil-N,N'-diciclohexilisoureas. Los alil y bencil ésteres fueron preparados bajo condiciones suaves, en cortos tiempos de reacción; los rendimientos elevados y la alta pureza de los productos favorecen este procedimiento. Se presenta, además, la asignación completa de las señales de RMN para 1 H y 13C de los compuestos sintetizados.