TRIMETHYL SILOXY GROUP

A proposed mechanism for silyl ether displacement is shown in Scheme 6.14. In the first step, the fluoride anion converts the trimethyl siloxy group into a phe-nolate salt. In the following step, the phenolate anion attacks the activated fluoro monomer to generate an ether bond. The amount of catalyst required is about 0.1-0.3 mol%. Catalyst type and concentration are crucial for this reaction. 

Fluoro-A -sulfanes, such as sulfur tetrafluoride, diethylaminosulfur trifluoride (DAST) ° and piperidinosulfiir trifluoride,are able to selectively substitute the trimethyl-siloxy group by fluorine under mild conditions. 

The construction of the tricyclo[5.2.0.02,6]nonane (26, n = 1) and tricyclo[6.2.0.02,7]decane (26, n = 2) frameworks involved the [2 4- 2] cycloaddition of readily accessible31,32 l,2-bis(trimethyl-siloxy)cyclobutene and cnone 25, n = 1 or 2, respectively.33 The yields (75-80%) were good for adducts 26a, c, e, and g. Lower yields (40-50%) were observed for adducts 26b and 26f, while adduct 26d was only isolated in a trace amount. The most interesting and important reaction, related to the total synthesis of eudesmane sesquiterpenes, was the photochemical reaction of (-)-piperitone (25g) with l,2-bis(trimethylsiloxy)cyclobutene, which gave c/.v,(5wf/u W-2/j,7/i-dimethyl-4/ -isopropyl-l f ,8Jf -bis(triniethylsiloxy)tricyclo[6.2.0.0z 7]dec-3-one (26g) with the relative cis configuration of the methyl (R2) and isopropyl (R3) groups.33,34 Some of the other photochemical [2 + 2] cycloaddition reactions utilizing l,2-bis(trimethyl-siloxy)cyclobutene are shown by the formation of 2735,36 and 28.37... 

H9. Hunter, M. J., E. L. Warrick, J. F. Hyde, and C.C. Currie Organo-silicon polymers II. The open chain dimethyl oxanes with trimethyl-siloxy end groups. J. Am. Chem. Soc. 68, 2284—22 (1946). 

The bicyclic a-hydroxy acid 10a was obtained from the ring contraction of the 7,8-bis(trimethyl-siloxy)bicyclo[4.2.0]oct-3,7-diene (product of an acyloin cyclization) either by selective bro-mination at — 40 °C and subsequent hydrolysis or by simple autoxidation under an air stream. On further bromination at 20 °C and subsequent solvolysis in aqueous sodium hydroxide the hydroxycyclopropanecarboxylic acid 10a was transformed into 4-bromo-6-oxatri-cyclo[3.2.1.0 ]octane-7-carboxylic acid (11) by intramolecular cyclization, resulting from the addition of the c <7o-hydroxy group to the cyclohexene double bond. Formation of the product resulting from the addition of the carboxy group was not observed. ... 

Similarly, p3ridine addition to aldehydes is also promoted by TMSOTf in a three-component reaction to form [l-(trimethyl-siloxy)alkyl]p3Tidinium salts (eq 62), which may act as group transfer reagents or as precursors for the analogous phosphonium... 

Yamashita et al. obtained polydimethyl siloxane macromer through polymerization of dimethylsiloxane cyclic trimer, initiated by trimethyl siloxy lithium. The reaction was terminated by compounds containing both chlorine and vinyl groups, to obtain the desired macromer. 

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