Silanimines cycloadditions

The formation of silanimines can further be proven by trapping reactions. One such reaction is the [2 + 3] cycloaddition with azides to give siladihydrotetrazoles 344a (equation 227). 

Lithiated fluorosilanes such as 801 and 802 may be considered as fluoride donor adducts to silanimines and behave as the free silanimines (e.g. 803) in cycloaddition reactions with C=0 compounds. The stability of the four-membered cycloadducts obviously depends on the substituents (equation 274)355. 

Reactions of 59 with less hindered azides can be more complex. With trimethylsilyl azide, the isolated product was the azidosilane 73. The formation of 73 can be rationalized, however, as proceeding through the initial formation of a silanimine, followed by addition of MesSi—N3 across the Si=N double bond, as shown in equation 110. When 59 was treated with 1-adamantyl azide, the product was the silatetrazoline 74. Once again this product may have resulted from initial formation of a silanimine, followed in this case by 2 + 3 cycloaddition of the azide to the Si=N double bond (equation 111)98 148. 

This is contrary to the result of the reaction of Me2(H)SiNLiCMe3 with methacrolein in presence of MesSiCl in -hexane. In this case the amide behave like a silanimine. The imine CH2=C(Me)-CH=NCMe3, the cyclosiloxanes (Me2SiO) ( = 3, 4) and MesSiH are obtained (Scheme 3). The imine and the cyclosiloxanes are produced via an oxaazasilacyclobutane intermediate, fomed by [2+2] cycloaddition of the silanimine Me2Si=NCMe3 with the aldehyde. 

A novel approach to silanimine involves a form of double bond exchange using a silene57,211. It is probable that a cycloaddition product of the silene is first formed, and subsequently the silanimine is eliminated (equation 20). Although the approach relies on the formation of silene, it still may provide a viable route to additional silanimines. 

---