Silyl fluoride

The effect of the AK = 1 selection rule, compared with AK = 0 for an transition, is to spread out the sets of P, Q, and R branches with different values of K. Each Q branch consists, as usual, of closely spaced lines, so as to appear almost line-like, and the separation between adjacent Q branches is approximately 2 A — B ). Figure 6.29 shows such an example, E — A band of the prolate symmetric rotor silyl fluoride (SiH3F) where Vg is the e rocking vibration of the SiH3 group. The Q branches dominate this fairly low resolution specttum, those with AK = - -1 and —1 being on the high and low wavenumber sides, respectively. 

The C-Si bonds of aryl-, heteroaryl-, vinyl-, and allylsilanes are stable towards alco-holates or weak reducing agents, but can be cleaved under mild conditions by treatment with acids or fluoride to yield a hydrocarbon and a silyl ester or silyl fluoride. Several linkers of this type have been tested and have proven useful for the preparation of unfunctionalized arenes and alkenes by cleavage from insoluble supports. Typical loading procedures for these linkers are sketched in Figure 3.42. 

The fact that known anionic initiators for MMA can act as catalysts for GTP and the need for low amounts of catalysts in itself nearly puts to rest the associative mechanism. Seven of the other factors support the dissociative process. Except for the low temperature exchange studies, none supports the associative mechanism. Based on the lack of exchange of added silyl fluoride with silyl ketene acetal ends it looks like fluoride and bifluoride catalysts operate by irreversible generation of ester enolate chain ends [1] (Scheme 19b). On the other hand carboxylate catalysts appear to operate by reversible generation of ester enolate ends as evidenced by rapid exchange of silyl acetate with silyl ketene acetal ends [36] (Scheme 19c). 

CaC03433. Silyl fluorides can also act as electrophiles for the silylation of intermediate 161434. 

Elaboration of 3.119 (prepared as in Fig. 3.45) to 3.121 (steps a,b. Fig. 3.46) was performed in standard experimental conditions. Final cleavage of 3.121 to 3.107 (steps c,d) was better performed using a recently developed traceless residue protocol (32) which converts fluoride anions to volatile silyl fluorides which are evaporated from the solution together with pyridine. The product 3.107 was obtained in a good 37% overall yield, calculated for the entire 14-steps SP protocol starting with the loading of 3.112 onto PS-DES resin. 

Alkoxysilanes, however, react with COFj (at 0-20%) in a similar way to that described for COClj to give silyl fluoride and alkyl fluoroformate derivatives [1452] in high yields ... 

It is possible for organosilyl compounds with a leaving group at the fi position to undergo E2-type reactions induced by cesium fluoride. In deprotonation-ehmina-tion, a strong base such as amide or alkoxide is required the conjugated acid produced by deprotonation (e.g. amine or alcohol) may react with the elimination product. In the case of cesium fluoride-induced desilylation-elimination, the formed conjugated acid is silyl fluoride which is unreactive. The production of unstable products such as cyclopropene (Scheme 2.13), cyclohexene-3-yne (Scheme 2.14), or orthoquinodimethane has been reported [24—29]. 

Biginelli reaction (Scheme 3.12) [64,67]. Excess (3-ketoester and aldehyde was separated from the fluorous reaction product by partitioning between toluene and FC-84 (mixture of isomers of C7Flft). The same system was used after cleavage of the silyl group with TBAF. In this case the toluene extracted the desired product while the fluorous silyl fluoride remained in the fluorous phase. 

B-Fluoroborazines have also been prepared by elimination of silyl fluorides. Facile cleavage of the Si—N bond renders silylamines very effective in the synthesis of these and other B-haloborazines, and they are extensively utilized. Reactions involving elimination of silyl halides have been found particularly useful in sterically hindered systems. ... 

Transition states for inversion and retention of configuration channels in the reactions of alkyl and silyl fluorides with a water molecule " ... 

An early observation in the development of fluorosilane cross-coupling noted the affect of heteroatom substitution at the silicon on the facility of coupling. In the cross-coupling reactions between (l-octenyl)silyl fluorides and 1-iodonaphthalene, it was determined that fluoride substitution on silicon was essential for the reaction... 

Aminonaphthylsilanes with CsF/imidazole discriminates 1 and 2 OH groups of serine n-butylamide to give fluorescent 3 silyl ethers which can be cleaved by HP t6 form fluorescent silyl fluorides. Photolysing ketene in the presence of methylfluorosilanes gives... 

Other Reactions. Trityl fluoroborate has been used often to prepare cationic organometallic complexes, as in the conversion of dienyl complexes of iron, ruthenium, and osmium into their cationic derivatives. It alkylates pyridines on the nitrogen atom in a preparation of dihydropyridines and acts as a tritylating agent. It has also been used in attempts to form silyl cations and silyl fluorides from silanes. Finally, it has been reported to be a usefiil desiccant. ... 

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