Silyl hydroxylamines

Using trimethylsilyl triflate, a one-pot reaction of acetoxyallylation and O-silylation of nitrones, gave silylated hydroxylamines (673). Enantiomers of the naturally occurring alkaloid dihydropinidine, potential antifeedants against the pine weevil Hylobius abietis, were prepared by diastereoselective, dimethylzinc mediated addition of pinacolyl 2-propenylboronate to (/ )- and to (S )-2-methyl tetrahydropyridine-A-oxide, obtained from D-alanine and L-alanine, respectively (Scheme 2.190) (674). 

Following a similar approach, the first bis(triorganosilyl) diazene 402 that is stable at room temperature could be obtained.410 Thus, the reaction of (/-Bu2MeSi)HNNH(SiMe/-Bu2) 403, an analog of 399, with 2 equiv. of BuLi has provided (/-Bu2MeSi)LiNNLi(SiMe/-Bu2) 404, whose oxidation with bromine has led to the formation of the diazene /-Bu2MeSiNNSiMe/-Bu2 402 (Scheme 58). Recently, the stepwise synthesis of cyclic and open-chain silyl hydro-xylamines has been reported by Klingebiel < / /.411 14 For hypervalent silyl hydroxylamines, see Section 6.8. 

Recently, density functional calculations (B3LYP) on the thermal rearrangement of tris(silyl)hydroxylamines to silylamino disiloxane for model compounds concluded that the insertion of a silyl group into the N—O bond is energetically favoured if it occurs from the nitrogen atom. ... 

To explore the dyotropic rearrangement of silyl hydroxylamines, Schmatz, Klinge-biel and colleagues studied the behaviour of 0-lithium-Af,Af-bis(f-butyldimethylsilyl) hydroxylamine 207 in the presence of chlorotrimethylstannane (equation 62). They found that the primarily formed Af,Af-bis(f-butyldimethylsilyl)-0-(trimethylstannyl)hydroxyl-amine 208 underwent a dyotropic rearrangement to form 209. This reaction mechanism is corroborated by quantum chemical calculations partly employing an effective core potential for tin. 

Benzoyl-l-(4-brom-phenyl)-4,5-dimethyl-l. 2,3,6-tetrahydro-pyridin (52% bez. auf die Gesamtreaktion)2 2- Benzoyl-4,5-dimethyl-1-( 4-methyl-phenyl)-l, 2,3,6-telrahydro-pyridin (36% bez. auf die Gesamtreaktion)2 2-Benzoyl-4,5-dimethyl-l-phenyl-l,2,3,6-tetrahydro-pyridin (52% bez. auf das intermediate O-Silyl-hydroxylamin-Derivat)2... 

The interaction between oximes and triethylsilyl radical has been investigated by ESR, which showed that an a-silylated hydroxylamine is formed. In spite of the lack of any further detail, this reaction may constitute an excellent access to this type of SMA... 

Fluorosilylhydroxylamines 2 contain two functional groups N-H and Si-F. Treatment of fluorosilylhydroxylamines 2 with butyllithium results in ring closure to yield the cyclic silyl-hydroxylamines 3 containing a six-membered ring [1]. 

The concluding part of this section deals with some structural aspects of the genesis of the ion Me3SiOSiMe2 (44) which is ubiquitous in the mass spectra of bis-silylated compounds, and some examples for its formation have already been given in reactions 31 and 42. Ion 84 (reaction 41) upon collisonal activation also dissociates to Me3SiOSiMe2. Formally related with the process 85- 44 (reaction 42) is the 1,1-elimination of the nitrene RN from the [M — Me]+ ions of the corresponding bis-silylated hydroxylamine derivatives 89 (reaction 43)69. 

Systematic studies of related rearrangements in tris(silyl) hydroxylamines have been reported by West and co-workers (50, 51), the results of which are described below. 

The simplest silylated hydroxylamine, Me2NOSiH3 (Fig. 3), shows a small Si-O-N angle of 102.6(1)° and a short Si -N distance of 2.453(1) A. This is much smaller than in the isoelectronic compound isopropoxysilane, H3SiOCHMc2, which is not capable of forming a 3-donor bond due to the absence of a lone pair of electrons. Comparison of the angles Si-O-C/Si-O-N shows the 3-donor-acceptor interaction in Me2NOSiH3 to be responsible for a compression of almost 16°. 

Pioneering work in the synthesis and in studies of rearrangements in tri(organyl)silyl-hydroxylamines was done in the groups of Wannagat and West [1]. 

C In the reaction of bis(silyl)hydroxylamines with lithium, oiganic lithium always attacks the oxygen atom. This includes an anionic 1,2-silyl group migration from oxygen to the nitrogen atom. Isomeric bis(silyl)hydroxylamines form the same lithium compound which reacts with... 

For a better understanding of our results we report quantum chemical investigations of the isomerizations of tris(silyl)hydroxylamines for several model compounds and the thermal rearrangements of two N,N,0-tris(silyl)hydroxylamines with formation of the isomeric silylaminodisiloxanes. 

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