Silyl oxides

Diisopropylamino(dimethyl)silyl]-2-propenyl]lithium adds to aromatic and x-branched aldehydes in the presence of anhydrous zinc chloride with essentially complete anti stereoselectiv-ity3s. as expected from the chair-like pericyclic transition state formed by the ( -intermediate. The addition products are not isolated, but after O-silylation, oxidative desilylation with retention of configuration forms the rmft-diols. 

The expected preparation of Mes P=C=0 or Mes P=C=PMes in a single step from the reaction of silylphosphide lib with carbon dioxide resulted in the isolation of phos-phino(silyloxy)phosphaethene 13 (equation 91)91. Proton abstraction from 13 with one equivalent of n-butyllilhiurn in ether at room temperature caused elimination of silyl oxide and resulted in the formation of the first stable diphosphaallene Mes P=C=PMes91. 

Scheme 11 summarizes the reactions of bis(diisopropylamino)lithiocyclopropenylium perchlorate with a variety of electrophiles. These include acid hydrolysis, silylation, oxidative coupling with iodine to the symmetrical tetraisopropylamino triafulvalene dica-tion, reaction leading to C—C bond formation, with electrophilic allenes to give a zwitterionic dihydrotriafulvenes, with disubstituted cyclopropenylium perchlorate, and... 

C6H15N02 N,N-dimethylacetamide dimethyl acetal 18871-66-4 391 15 33.532 1,2 9363 C6Hl80Si2 bistrimethyl silyl oxide 107-46-0 373.67 31.892 2... 

Reactions with aldehydes and ketones Silylation Oxidation... 

The key skeleton of 120 was constructed via the Petasis-Ferrier rearrangement [17], established by Smith as a powerful, stereocontrolled entry to ci5-2,6-disubstituted tetrahydropyran (Scheme 24) [18,19]. Brown asymmetric allylation of the known aldehyde 124 [69] installed the C-11 asymmetric center in 91% ee to give 125 after silylation. Oxidative cleavage of the terminal alkene, followed by silylation, delivered the /8-hydroxy ester 126, which was condensed with aldehyde 127 mediated by TMSOTf (but the actual catalyst was found to be TfOH) to furnish an inseparable mixture of the... 

On the other hand, elimination under basic conditions should proceed in a syn manner. Two possible pathways have been postulated for the elimination of a silyl-oxide moiety after deprotonation of a hydroxy group with an equimolar amount of base (Scheme 2.4). One is the stepwise 1,3-migration of a silyl group from carbon to oxygen, followed by elimination of a trimethylsilyloxide moiety. The other involves the formation of a pentacoordinate 1,2-oxasiletanide 2, which is in equilibrium with the j8-silylalkoxide anion 1, and extrusion of the trimethylsilyloxide moiety therefrom. The reaction mechanism has not yet been entirely elucidated. 

In the stepwise mechanism, the stereospedficity of the elimination of the silyl-oxide from the -hydroxyalkylsilane can be explained as follows. Both migration of the sUyl group from carbon to oxygen and elimination of the trimethylsilyloxide moiety to form a double bond are so rapid that no rotation about the C-C bond is usually observed during these steps, giving the alkene with the same stereochemistry as that obtained by a concerted mechanism. 

Shankar K, Jackson TN (2004) Morphology and electrical transport in pentacene films on silylated oxide surfaces. J Mater Res 19 2003-2007... 

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