Bis , allylic diradicals

Tetramethylene-ethane (TME), or 2,2/-bis-allyl diradical 81, was suggested as an intermediate in the thermal dimerization of allene, as well as in the interconversions of 1,2-dimethylenecyclobutane 82, methylenespiropentane 83, bis-cyclopropylidene 84 and other bicyclic systems (equation 30)45. The isolation of two different isomeric dimethylene cyclobutanes 87 and 88 (in a ca 2 I ratio) after the thermal rearrangement of the deuteriated 1,2-dimethylene cyclobutane 85 suggests that the rearrangement proceeds via a perpendicular tetramethyleneethane diradical (2,2/-bisallyl) 86 (equation 31)45. 

The reaction of keten dimethylacetal with 3-acetoxycyclohex-2-en-l-one gives rise to the stable, easily handled, fused cyclobutene (392), further reaction of which, followed by oxidation, resulted in the naphthacenetrione (393). The naphthacenes (394) originate by dimerization of the polyphenyl-allenes R CCl=C=CR2ph (R = Ph, R = C1 R = C1, R = Ph), by way of bis-allyl diradicals, the dihydronaphthalenes (395), and then the naphthocyclobutenes (396). 

Density functional theory computational studies have been used to determine die importance of secondary orbital interactions for the stability of transition-state structures for die 4 + 2-cycloaddition of furan with cyclopropene.175 Kinetic studies of die 2 + 4-cycloaddition of 2-cyclopropylidene acetates with furan and dimethylful-vene suggest a mechanism involving diradicals or zwitterions as intermediates.176 Cyclopropene, produced by die reaction of allyl chloride with sodium bis(bimediyl-silyl)amide, reacts with 1,3-diphenylisobenzofuran to produce both endo- and exo-Diels-Alder cycloadducts isolated for the first tune.177... 

It was suggested that in the photochemically triggered oxidation of phenol by Ru(bpy)3, the proton charge was delocalized over a primary shell of water molecules firmly bound to the pyridinium cation.The tetra-2-oxypyridinate ruthenium(II, III) dimer [Ru2(hp)4Cl] and related diruthenium adducts were effective catalyst for the oxidation of allylic and benzylic C—H bonds. The bis(homoallylic) sulfamate esters were converted to the corresponding allylic amines using PhI(02C Bu)2 in CH2CI2. Both computational and experimental studies favoured a stepwise mechanism involving H atom abstraction/radical recombination and the intermediacy of a discrete short-lived diradical species. ... 

---