Endocyclic diene structures

Depending on the nature of both the halogen and the metal, the group 14 metalloles can react with halogens in three different ways (i) addition of 1 or 2 equivalents of halogen to the diene system, with the cyclic structure preserved, (ii) cleavage of one or two endocyclic E-C bonds, with destruction of the cyclic structure, and (iii) substitution of one or two exocyclic substituents, with preservation of the metallole structure. 

Hexakis(2,4,6-triisopropylphenyl)tetragermabuta-l,3-diene 182 was obtained and converted upon treatment with sulfur into thiatetragermacyclopentene 183 with an endocyclic Ge=Ge bond. The reaction of 183 with dry air furnished a 2,4,7,8-tetraoxa-l,3,5,6-tetragermabicyclo[4.1.1]octane derivative 184 (Scheme 33). Structures of 183 and 184 were confirmed by X-ray crystallographic analysis <20030M1302>. 

Amino-5-methylthiazole)(l,4,7-triazaheptane)copper(ll)] dinitrate was characterized by X-ray diffraction. There were two crystallographically discernible cations [(amtz)(dien)Cu] and four NOs ions in the asymmetrical unit of the structure. Dien is tridentate with mean Cu-N = 1.997(5) and 2.021(5) A in the two Cu-ions, respectively. The thiazole ligand is coordinated through its endocyclic N with Cu-N = 2.063(7) and 1.945(6) A in the two ions,... 

It thus appears that the principal structural features found In poly(1,4-dimethylenecyclohexane) can be explained by conventional carbonium ion chemistry. There is no indication that cyclopolymerization occurs in these polymerizations and there is much evidence to indicate that the double bonds present in this diene react independently. Some of them are involved in polymerization reactions, but a large proportion isomerize to relatively stable endocyclic double bonds. Under polymerization conditions where isomerization is favorable, soluble, unsaturated polymers having complex structures are obtained. When isomerization reactions are not favorable (low temperatures, use of Ziegler-Natta catalysts), the double bonds polymerize independently and crosslinked products are obtained. 

Complete lineshape analysis of the ABCj DEF2 exchange process observed in the n.m.r. spectra of 2,6-disubstituted homotropylidenes has been employed in the evaluation of the thermodynamic parameters for Cope rearrangement, The phenyl groups at the 2,6-positions of the barbaralane (155) destabilize the transition state relative to the unsubstituted hydrocarbon (154) as evidenced by the AGj g values, respectively 9.3 and 7.6 ( 0.1) kcalmol" Kinetic data for the Diels-Alder addition of acrolein to cydohexa-1,3-diene, and its reverse reaction, in the gas phase have been interpreted in favour of a biradical mechanism. Both the heat and entropy of formation of the endo-adduct have been estimated. Structural modification of 2,3-dimethylenenorbornane (156) or of 2,3-dimethylenenorbornene (158) by the introduction of oxygen in place of C-7, as in (157) and (159) respectively, leads to a decrease in rate of Diels-Alder reaction of the dienes with dimethyl acetylenedi-carboxylate. The double bond in (158) likewise resulted in deactivation relative to (156), and epoxidation of the endocyclic double bond in (158) also afforded an s-cis-diene of decreased reactivity. 

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