Chalcogen-rich Rings

Monomers of the type R2M=E (M = Si, Ge, Sn, Pb, E = S, Se, Ge, Pb) involving the heavier group 14 and group 16 elements are of fundamental interest as congeners of ketones R2C=0. As such, they are referred to as heavy ketones . 

The desulfurisation of a tetrathioplumbolane Ar(Ar )PbS4 with different substituents on the lead centre unexpectedly produces the four-membered 

Armitage, Inorganic Rings and Cages, Edward Arnold, London, 

Shimoda, Y. Matsuki, M. Furusawa, T. Aoki, L Yudasaka, H. Tanaka, 

Haiduc and M. Drager, in The Chemistry of Inorganic Homo- and Heterocycles, ed. I. Haiduc and D. B. Sowerby, Academic Press, London, 1987, Vol. 1, pp. 361-365. 

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J. Beck, Rings, cages and chains - the rich structural chemitry of the polycations of the chalcogens. Coord. Chem. Rev. 163 (1997) 55. 

In view of the preference of the tetrasilabuta-1,3-diene 139 for the s-cis form, it seemed worthwhile to examine its behavior in [4 + 2] cycloadditions of the Diels-Alder type. Since 139, like many disilenes, should behave as an electron-rich diene, we attempted to react it with various electron-poor and also with some electron-rich olefins. No reaction was detected in any case. Only in the presence of water did 139 react with quinones to furnish the unsymmetrically substituted disilenes 36 and 37 (see Section III.A). The effective shielding of the double bonds by the bulky aryl groups and, above all, the 1, 4-separation of the terminal silicon atoms of about 5.40 A appear to be responsible for these failures. Thus, it was surprising that treatment of 139 with the heavier chalcogens afforded five-membered ring compounds in a formal [4 + 1] cycloaddition (see below). 

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