Benzoquinone, chromium complexes

The closely related oxo-bridged complex [(H20)5CrOCr(H20)5]4+ is obtained in low yields on the reduction of 1,4-benzoquinone by aqueous solutions of chromium(II).710 The sole product of the hydrolysis of this dimer711 (HC104/LiC104 / = 1.0) is hexaaquachromium(III). 

Alternatively, chloroarenes can be activated via the formation of manganese, chromium, iron or ruthenium 7r-complexes that react at low temperature with phenoxides to yield diaryl ethers [14], Higher temperatures (DMF, 90 °C) require the formation of diaryl ethers from iodonium salts and phenoxides [15] and the coupling of bromo benzoquinones with phenoxides (DMF, 100-110 °C) followed by a subsequent reduction with dithionite [16]. 

Hydroxycyclopentanones and hydroxycyclohexanones are both accessible by ring expansion of such strained rings as are present in cyclobutanone and cyclobutenedione. Two examples of such ring expansions are given (see Schemes 7 and 9) the first, to a cyclopentanone, is mediated by diazomethane, and the second to a cyclohexadienedione (a benzoquinone) with an alkynyllithium (see Scheme 9). In the first example, a chromium carbene complex 43 was combined with a chiral racemic aryloxazolidinone (44) to produce the cyclobutanone 45,... 

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