Silacyclobutenes synthesis

M. Backer, M. Grasmann, W. Ziche, N. Auner, C. Wagner, E. Herdtweck, W. Hiller, M. Heckel, Silacyclobutenes — synthesis and reactivity, in Organosilicon Chemistry II— From Molecules to Materials (Eds. N. Auner, J. Weis), VCH-Verlagsgesellschaft, Weinheim, 1996, p.41. 

A review on the synthesis and properties of phosphetanes has appeared <02CRV201>. The first isolation and crystallographic results of a Pt-containing silacyclobutene, the stable 4-sila-3-platinacyclobutene 59, has been described and its formation pathway was demonstrated via Pt-promoted y-Si-H bond activation of a 3-sila-l-propenylplatinum precursor <02JACS4550>. 

The first synthesis of a silacyclobutene diannelated [a,d benzene (60), <02OM1101> as well as the preparation of novel l-aza-2-silacyclobut-3-enes 61 appeared in the literature <02JCSD3253>. 

Summary Cl2Si=CHCH2/Bu is a versatile building block in organosilicon synthesis which reacts with a wide variety of multiple bond systems. The unique reactivity is shown by the predominance of [2+2] over [4+2] cycloaddition reactions. This unusual behaviour is caused by the two chlorine substituents at the silicon atom. This presentation shows the synthesis of silacyclobutenes from Cl2Si=CHCH2tBu and disubstituted alkynes and some chemistry of these four membered ring compotmds. 

In this chapter, the scope, mechanism, and recent progress of zirconocene (Il)-mediated cyclization reactions are introduced. Zirconocene(II) is a very important reagent for organometallic chemistry, synthetic chemistry, and polymer chemistry. Zirconocene(II) is capable of coordinating with unsaturated compounds. Further reactions could lead to zirconocene(IV) species, zirconacycles, C-C bond formation, C-X bond formation, and synthesis of carbocycles and heterocycles. Zirconocene(lI)-mediated cyclization of bis(alkynyl)silane gives zirconacyclobu-tene-silacyclobutene complexes, which could react with alkyne, bis(alkynyl)silane, ketone, nitrile, and isocyanate and could be applied in the synthesis of various valuable products. 

Liu J, Zhang S, Zhang W-X et al (2009) Star-shaped silacyclobutene-containing n-systems synthesis and optical properties. Organometallics 28 413-417... 

Jin CK, Yamada T, Sano S et al (2007) Stereoselective synthesis of unsymmetrical conjugated dienes and trienes utilizing silacyclobutenes. Tetrahedron Lett 48 3671-3675... 

The reaction of zirconacyclobutene-silacyclobutene fused compound 46 formed from Si-tethered diyne 45 with Cp2Zr(II) species has been used in the synthesis of fused aromatic heterocycles 47 (Scheme 11.18) [20]. When the zirconacycles 46 reacted with nitriles, the corresponding pyrrolo[3,2-c]pyridines 47 were formed. This indicates the unexpectedly strong effects of the alkynylsilyl groups on this unusual skeletal rearrangement of zirconacycles. 

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