Substituted silole derivatives

Lithiation of l-bromo-4-trisubstituted silylbuta-1,3-diene derivatives with r-BuLi has afforded substituted siloles (35) in high yields (e.g. Scheme 17).93 A pentaorgano-silicate has been proposed to be the intermediate for this reaction. Selective cleavage was observed when the silyl group possessed different substituents. Results have shown that vinyl and phenyl substituents on the silicon atom were substituted much... 

Considering the peculiar contribution of the central silicon atom to the --electronic structure of silole derivatives through a -n conjugation, other Group 14 metalloles are also of interest. To elucidate the effects of the central Group 14 elements, we have prepared a series of 2,5-dithienyl-substituted Group 14 metalloles, cyclopentadiene 30, siloles 26m and 27, germole 31 and stannole 32, and compared their photophysical... 

The organometallic-substituted 85 (M = a derivative of B, Zn, Sn) and halogeno-substituted siloles 85 (M = C1, Br, I) are suitable starting compounds for cross-coupling reactions. Pd-catalyzed coupling of 91 (R = Me, Ph) with 4-amino- and 4-heteroaryl-bromobenzenes affords the siloles 92 in high yield <20040M6205>. 

Space precludes an extensive survey of silicon, germanium, tin and lead substituted derivatives of cyclopentadiene (the siloles and analogues). Until 1979, few plumboles were known (79RTC437), but now, with the siloles, germoles and stannoles, they represent one of the most extensively studied areas of Group IV substituted heterocyclic chemistry. The references prefacing Section 1.20.9 cover reviews for this section. 

Owing to the lability of the tin-carbon bond, stannoles were the first heterocyciopentadienes to be transformed into other heteroles boroles , arsoles or stiboles ° and auroles. However, since their synthesis is presently less easy for the C-unsubstituted or alkyl substituted derivatives than in the case of the corresponding siloles or germoles, they are not useful reagents for preparing these heteroles. 

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