α,β-Unsaturated and cyclopropyl acyl radicals, and their ketene alkyl radical equivalents. Ring synthesis and tandem cyclisation reactions

Crystal structures of two bi-cyclo-[5.1.0]octa-nes: potassium trans-bi-cyclo-[5.1.0]octane-4-carboxyl-ate monohydrate and cis-bi-cyclo-[5.1.0]octan-4-yl 4-bromo-benzene-sulfonate

The crystal structures of the trans-fused compound potassium trans-bi-cyclo-[5.1.0]octane-4-carboxyl-ate monohydrate, K+·C9H13O2-·H2O, (I), and of cis-bi-cyclo-[5.1.0]octan-4-yl 4-bromo-benzene-sulfonate, C14H17BrO3S, (II), have been determined. Compound (I) represents the smallest trans-fused cyclo-propane structure known to date, and features the expected shortening of the bridging C-C bond relative to the other cyclo-propane bond lengths, in contrast to the cis-fused system, (II), where all of the cyclo-propane bond lengths are the same. The bicyclic ring system of (I) is disordered across a crystallographic mirror plane. The geometries of the cis-fused and trans-fused ring systems are compared.

Generation of Phosphorus-Centered Radicals via Homolytic Substitution at Sulfur

A novel radical domino process relying on the homolytic cleavage of P-S bonds allows the preparation of phosphorus-containing molecules through addition of P-centered radicals onto olefins. The key step of this reaction is a homolytic substitution on a sulfur atom. The scope of the reaction is broad. Diaminophosphonyl radicals whose reactivity was unknown react smoothly with olefins. Use of tin hydride can be avoided. A radical thiophosphinoylation of triple bonds has been uncovered. [reaction: see text]

Synthetic studies towards furanocembrane diterpenes. A total synthesis of bis-deoxylophotoxin

Synthetic approaches to the furanocembrane family of natural products, e.g. lophotoxins, pukalides, bipinnatins, based on: i) an intramolecular cyclisation of an alpha,beta-unsaturated acyl radical intermediate into a conjugated enone, and ii) an intramolecular Stille coupling reaction involving a 2-stannylfuran and a vinyl iodide, are described. A total synthesis of bis-deoxylophotoxin , the probable biological precursor to the neurotoxin lophotoxin, isolated from species of the Pacific sea whip Lophogorgia, is then presented.

Tandem cyclisations involving α-ketenyl alkyl radicals. New syntheses of the natural triquinanes pentalenene and modhephene

New synthetic approaches to the angular and propellane sesquiterpene triquinanes (+/-)-pentalenene 2 and (+/-)-modhephene 3, respectively, are described. The syntheses are based on tandem cyclisations involving alpha-ketene alkyl radical intermediates produced from alpha,beta-unsaturated acyl radical species, as highlighted in Schemes 2 and 4.