Arylsilicon

Mardniec, B., Pietraszuk, C., Kownacki, 1. and Zaidlewicz, M. (2005) Vinyl- and arylsilicon, germanium, and boron compounds, in Comprehensive Organic Functional Group Transformations II, Vol. 1 (eds A.R. Katrytzky and R.J.K. Taylor), Elsevier, Amsterdam, pp. 941-1024. 

The unique hormonal activity of siloxanes is limited to methylaryl-substituted, linear di- and trisiloxanes and cyclic tri- and tetrasiloxanes (67, 75, 76, 81). In general, at least one arylsilicon grouping is necessary for activity. The substitution of an alkyl group for a phenyl group either decreases the activity markedly or eliminates it entirely. Cyclosiloxanes... 

A rhodium(l)-catalyzed system in THF is also effective in the Mizoroki-Heck-type reaction of arylsilanediols with acrylates (Scheme 4).53 Interestingly, the use of aqueous THF switches the reaction to 1,4-addition forming /3-arylated esters. The proposed catalytic cycles for these reactions involve 1,4-addition of an arylrhodium species to an acrylate. The change of the reaction pathway is probably because, in aqueous THF, the resultant Rh enolate 6 undergoes protonolysis rather than /3-elimination. Similar Rh-catalyzed 1,4-additions to a,/3-unsaturated carbonyl compounds have been achieved with arylsilicones,54 arylchlorosilanes,55 and aryltrialkoxysilanes.56,57 The use of a cationic Rh-binap complex leads to highly enantioselective 1,4-additions of alkenyl- and arylsilanes.58 583... 

Arylsilicon bonds are more readily cleaved by Hg salts, especially with arylsilane-Hg(0Ac)j, e.g. ... 

Substitution of arylsilicon compounds without loss of silicon activation and... 

Nitration presents a special case where the Ar-H bond is cleaved more readily than the Ar-Si bond and there is no apparent reason why this should be the case. If nitro-desilylation requires nucleophilic assistance of the C-Si bond cleavage, the absence of a good nucleophile could explain the results obtained with nitronium tetrafluoroborate101. Substituents on the silicon have a profound effect on the reactivity of the arylsilicon... 

The starting materials can be prepared through hydrolyses of alkyl or arylsilicone halides. Organosilicone halides, in turn, are made commercially by heating alkyl or aryl halides with silicon at 250-289 °C. This reaction is catalyzed by copper ... 

Both above described strategies involving arylstannane and arylsilicon reagents proceed thanks to the readiness of the transmetallation reaction from tin or silicon to copper. 

Similar to organoboron reagents, silicon has drawn the attention of chemists for many years because of its low cost, large abundance, and nontoxic properties. However, conjugate addition with arylsilicon compounds was considered to be problematic because of their lower reactivity. These reagents work fine in the presence of air and water. Huang and Li [66], in 2001, also reported... 

The combination of silanes and silanols is not limited to simple methylsilicones or arylsilicones but can be extended to much more complicated systems. Kawakami and coworkers described the synthesis of complex double decker siloxanes and their alternating copolymerization with a dimethylsilicone chain (Fig. 15a) [65]. They have also shown that asymmetrical copolymers can be prepared enantiose-lectively using this strategy (Fig. 15b) [66]. 

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