Sila-Peterson reactions

TABLE 4. Silenes R1R2Si=CR3R4 synthesized by the sila-Peterson reaction and related reactions... 

Recently, Peterson-type reactions have been applied to the syntheses of transient and stable heavy element analogues of alkenes and alkynes. Transient and isolable silaethenes 207331 were prepared by the sila-Peterson reactions121,321,332 340. Similarly to the original Peterson reactions341,342, the sila-Peterson reactions were found to involve a 1,3-silyl migration from silicon to oxygen (equation 135)321. 

Scheme 3. The formation of the silanol 9, an acid-induced sila-Peterson reaction.

The mechanism of the formation of the silanol 9 (Scheme 3) is understood as the result of an acid-catalyzed formal elimination of dimethylaminotrimethylsilane generating the silene 7, followed by the addition of H2SO4 at the silene double bond and subsequent hydrolysis of the silylsulfate 8. To our best knowledge, this is the first case of an acid-induced sila-Peterson reaction. 

Scheme 2.157. Synthesis of silenes by the sila-Peterson reaction.

The first 4-silatriafulvene derivative 94 (R = Me) was obtained by Kira s group as a reactive intermediate using the sila-Peterson reaction [52]. By use of the bulky tert-butyldimethylsilyl groups rather than trimethylsilyl (TMS) substituents in 94, the first stable 4-silatriafulvene 95 was synthesized by the same group (Scheme 6.22). An X-ray analysis reveals that 95 has an almost planar skeleton with bond alternation all skeletal carbon and silicon atoms are located almost in a plane and the silicon-carbon double bond length is 1.755 A, which is close to that of tert-butyldimethylsilyl-(trimethylsUyl)adamantylidenesilane 96 (1.741 A) [53]. 

Since the isolation of the first example of a stable silene (1), compounds possessing silicon—carbon double bonds have been a focus of research because of their unique electronic properties and reactivities. However, the number of stable silenes remains very limited. Sila-Peterson reaction has proved to be a facile route toward the synthesis of stable silenes replacing photolysis and thermal treatments. 

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