Phosphorins radicals from

When cation-radicals from A3-phosphorins such as 188 are formed in the presence of nucleophiles and excess of oxidant, further reaction takes place to give A5-phosphorin derivatives, e.g., 191, generated in the presence of methanol by oxidation of 188 with mercuric acetate.611-614 A crystal and molecular structure determination of a A5-phosphorin shows a planar heterocycle with spd-hybridized phosphorus.615 Anion- and cation-radicals are also obtainable from the A5-phosphorin system.606,611,612... 

The position of phosphorus with respect to nitrogen in the periodic table led to the expectation that it should be much easier to remove one electron from X -phos-phorins than from pyridines (see also p. 37). Indeed, soon after the synthesis of 2.4.6-triphenyl-X -phosphorin 20 by Markl, we discovered that addition of 2.4.6-triphenoxyl 57 in benzene induces oxidation to the very stable radical cation 55... 

A third electron is then transferred from the contact with the K—Na alloy, forming the paramagnetic radical trianion 67. The phosphorus coupling constant in 67 of dp = 4,6 was calculated from the ESR spectmm of 2.4.6-tris-pentadeutero-phenyl-X -phosphorin. 

Oxidation of some 2,4,6-trisubstituted X -phosphorins by either chemical or electrochemical means gives short-lived cation-radical intermediates, which via the addition of water or methanol from the solvent afford radicals of the X -... 

The conversion of (298) into (300) upon gas-phase thermolysis occurs by a Cope rearrangement and not by a [1,3] carbon shift or a bisallyl radical mechanism. Thus, similar treatment of (299) affords only (301). Rearrangement of 3-oxobicyclo-[3,2,l]oct-6-ene to 3-oxobicyclo[3,3,0]oct-6-ene occurs only at much higher temperature and presumably by way of a non-concerted mechanism. The nickel-catalysed reaction of norbornene with butadiene affords the 1 2 cxo-adduct (302) which upon thermolysis is converted into the valence isomer (303). Concerted and non-concerted Claisen-type rearrangements have been observed in the A, -phosphorin series. Tricyclo[7,3,0,0 ]dodeca-2,5,7,10-tetraene (304), which is available in six steps starting from bicyclo[3,3,0]octa-3,7-dien-2,6-dione, appears to be an essentially static structure (as assessed by n.m.r. spectroscopy) up to 141 The slow... 

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