Efficient Intramolecular Cyclizations of Phenoxyethynyl Diols into Multisubstituted α,β-Unsaturated Lactones (original) (raw)
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Tetrahedron, 1987
We describe a new general method for the synthesis of medium-sized lactones based on ring-enlargement via a regioselective B-scission of alkoxyl radicals generated by photolysis from t&-hypoiodites of several catacondensed lactols. The syntheses of g-membered lactones from 6/5 fused lactols, lo-membered lactones including a naturally occurring lactone, phoracantholide I, from 6/6 or l/5 fused lactols, and 11-membered lactones from 7/6 or 0/5 fused lactols are shown to be achieved by the present method. This new method may have a potential for application to the synthesis of either smaller or larger-sized lactones.
Expedient Approach to α,β-Unsaturated δ-Lactones through a Catalytic Asymmetric [2+2] Cycloaddition
European Journal of Organic Chemistry, 2017
The stereoselective synthesis of cis-γ,δ-disubstituted α,βunsaturated δ-lactone fragment of leustroducsins or phoslactomycins was accomplished according to an original strategy involving a catalytic asymmetric ketene-aldehyde [2+2] cycloaddition leading to the formation of a cis-disubstituted β-lactone. Ring extension by enolate condensation and subsequent recyclization gave the target δ-lactone in a straightforward fashion. Coupling studies with cyclohexanone are also reported. Supporting information for this article is given via a link at the end of the document: copies of NMR spectra and XRay data
Journal of Heterocyclic Chemistry, 2015
A new rapid synthesis of γ-lactones, cis fused with a cyclopentenic ring by thermal cyclization of 7-chloro-2-(methoxycarbonyl)-4-6-dimethylocta-7-phenyl (or methyl) (2E,4E,6E)-trienoic acids was reported. The key step implicates an intramolecular cyclization to a cyclopentenyl cation, according to an electrocyclic π 2s + π 2a conrotatory process, published in a recent paper (from the corresponding diacids). We have investigated the thermal behavior of the corresponding half-esters since; if the cyclization obeys to the proposed mechanism, the diacids, half-esters must also cyclize in a similar manner. Saponification of these led to γ-dilactones via intermediary cyclopropanes. Mechanistic pathways were investigated.
Formation of macrocyclic lactones in the Paternò–Büchi dimerization reaction
Beilstein Journal of Organic Chemistry, 2011
Furan-2-ylmethyl 2-oxoacetates 1a,b, in which the furan ring and the carbonyl moiety were embedded intramolecularly, were synthesized from commercially available furan-2-ylmethanol and their photochemical reaction (hν > 290 nm) was investigated. Twelve-membered macrocyclic lactones 2a,b with Ci symmetry including two oxetane-rings, which are the Paternò–Büchi dimerization products, were isolated in ca. 20% yield. The intramolecular cyclization products, such as 3-alkoxyoxetane and 2,7-dioxabicyclo[2.2.1]hept-5-ene derivatives, were not detected in the photolysate.