Bicyclo octadiene complexes with

Another early success of the (TpRe(CO)(MeIm) fragment was the promotion of Diels-Alder cycloaddition reactions with benzene and anisole. Complex 101 [TpRe(CO)(MeIm)( 2-benzene)] undergoes an endo-selective Diels-Alder reaction with N-methylmaleimide to afford the bound bicyclo[2.2.2]octadiene complex 102 in 65 % yield (Scheme 12) [40]. Oxidation of 102 yields the bicyclo[2.2.2]octadiene 103 and/or the bicyclo[2.2.2]octenone 104 depending upon the choice of oxidation conditions. 

Similar stereoselectivities arc observed with nonconjugaled dienes which give bicyclic cyclobu-tanes with trans fusion of the annulated ring. Thus, 1,7-octadiene, treated with the same photochemically activated nickel complexes, gives trans-bicyclo[4.2.0]octane (6) in 21 % yield, after the resulting metallacycle is exposed to air24. 

Gold chloride forms an unstable complex with cyclo-octatetraene at low temperatures. This decomposes at — 20°C to l,2-dichlorocyclo-octa-3,5,7-triene, which gradually cyclizes to (562). In an attempt to form pentalene-metal complexes, cyclo-octatetraene was reduced to a mixture of trienes and bicyclo [4,2,0] octadiene, which was then treated with substituent ruthenium carbonyls, affording a variety of complexes, including (563). °... 

Metal-catalysed Isomerizations. The formation of 7r-allylchloropalladium(ii) complexes from a series of cyclopropenes proceeds with symmetrical complexation of the metal to the 7i-bond, and not a-bond cleavage, as the rate-determining step. With substituted cyclopropenes containing a phenyl group at C-3, the it-allyl complex rearranges to indenyl complex either spontaneously or on treatment with triphenyl-phosphine. trans-Chloropalladation of bicyclo[5,l,0]oct-3-ene has been described, and the complex decomposes not to cyclo-octadiene complex, but to a cyclo-octene n-allyl system. ... 

This equilibrium was first studied by Cope et a .54 in 1952. The Gibbs energy difference is small and the rate of interconversion slow at room temperature. Huisgen et al.55 examined the influence of variations of the ethane fragment on the position of the equilibrium. Attachment of a tricarbonyliron moiety apparently causes stabilization of the bicyclo[4.2.0]octadiene system,56 whereas with tricarbonylmolybdenum the monocyclic isomer is isolated as its metal complex.57... 

Martin and Eisenmann have re-investigated the thermolysis of syn- and anti-tricyclo[4,2,0,0 ]octane (511) and (512). Both ultimately give cis,cis-cyclo-octa-l,5-diene but the re-investigation shows that cis,trans-octa-l,5-diene is also produced and that it isomerizes to the all-cis-diene under the reaction conditions. The cis,trans-diene was trapped with hexachlorocyclopentadiene, and was also characterized as its dimer or its silver nitrate complex. Both (511) and (512) give mixtures of cis,cis-and cis,trans-octadiene in a co. 3 5 ratio. Thus the single-inversion pathway usually found in the pyrolysis of bicyclo [2,2,0] hexanes is also followed, at least partially, by... 

The condensation, reduction, cyclisation and methylation steps shown above result in an a-methoxy-y-pyrone unit appended to a linear polyketide-derived side-chain of varying degrees of reduction. However, the majority of y-pyrone-containing natural products isolated from sacoglossan molluscs do not possess linear side-chains, instead exhibiting complex carbon frameworks commonly characterised by cyclic motifs. For example, 9,10-deoxytridachione (2) [13] possesses a 1,3-cyclohexadiene unit, whilst ocellapyrone A (5) is endowed with a bicyclo[4.2.0]octadiene appendage (Fig. 1.1). 

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