Trimethylsilyl group, utility

The best carbonyl components for these reactions are highly electrophilic compounds such as glyocylate, pyruvate, and oxomalonate esters, as well as chlorinated and fluorinated aldehydes. Most synthetic applications of the carbonyl-ene reaction utilize Lewis acids. Although such reactions may be stepwise in character, the stereochemical outcome is often consistent with a cyclic TS. It was found, for example, that steric effects of trimethylsilyl groups provide a strong stereochemical influence.28... 

A closely related reaction having the phenol protected with a trimethylsilyl group was also examined (Scheme 31) [45]. Unlike the earlier examples, the cyclization reaction resulting from this substrate did not require the presence of a mild acid. The anodic oxidation in methanol solvent with no acetic acid led to a 73% yield of the tricyclic product. In a nearly identical reaction, an anodic oxidation of the trimethylsilyl-protected substrate in the presence of 2,6-lutidine led to the cyclized product in a 60% yield. The use of the silyl group expanded the utility of the anodic C-C bond-forming reaction being studied by allowing for the use of neutral and basic conditions. Hence, it would appear that the cyclization reactions are compatible with the presence of both base and acid sensitive functionality. 

The facile photochemical sigmatropic 1,3-trimethylsilyl shift in polysilylacylsilanes from silicon to oxygen (equation 33) was utilized historically to prepare the first relatively stable silenes3 86 87. Silenes prepared by isomerization of acylpolysilanes bear, due to the synthetic approach, a trimethylsiloxy group at the sp2-hybridized carbon and relatively stable silenes of this type have in addition also at least one trimethylsilyl group at the silicon. These substituents strongly influence the physical properties and the chemical behaviour of these silenes. This is noticeable in many reactions in which these Brook -type silenes behave differently from simple silenes or silenes of the Wiberg type. 

In addition to the regiocontrol, the use of SMA carbamates provides activation to the reaction through overlapping of the lone-pair electrons on the nitrogen with the s-orbital of the C-Si bond.96 In this process, the trimethylsilyl group is replaced by a methoxy group. In fact any nucleophile can be used. Thus, various carbanions were utilized for the synthesis of spiro compounds that are synthons, for example, in an excellent route to cephalotaxine.354... 

Zurmtihlen and Regitz prepared silyloxyiminophosphine by the condensation-silatropy method in the reaction of the silylphosphide lib with nitrosyl chloride (equation 96)70. The condensation-silatropy method has also been utilized for the introduction of pln=pln bonds. Romanenko and coworkers prepared diphosphene via phosphaethene (equation 97), in a reaction where one of the trimethylsilyl groups migrated onto the carbon atom121. 

One of the two hydrogen atoms of phosphoramidates can be temporarily blocked with a trimethylsilyl group. The sodium salt of diethyl V-(trimethylsilyl)phosphoramidate (102) reacted with alkyl bromides in benzene in the presence of 10 mol % of tetra-n-butylammonium bromide to afford, after desilylation, the corresponding V-alkyl derivatives (103) in 79-95% yields for primary alkyl halides. Secondary alkyl halides gave poor results (Scheme 43). The addition of the quaternary ammonium salt is essential to promote the alkylation reaction. Hexamethyldisilazane and its cyclic analogs can also be utilized in the preparation of amines under moderate conditions (Scheme 43). ... 

A more recent synthesis by our group utilized Mukaiyama s trimethylsilyl cyanide addition to aldehydes as the key step to introduce the carboxy functionality [33,36], This approach also required the preparation of (Z)-5-pentadecenal as the key intermediate, Fig. (12). In this case, commercially available decyl aldehyde was coupled with 4-carboxybutyltriphenylphosphonium bromide under Wittig conditions, resulting in a 10 1 mixture of the known (Z)- and ( )-5-pentadecenoic acids. The acids were then reduced to the desired (Z)-5-pentadecenal via (Z)-5-pentadecen-l-ol, a known pheromone. Addition of trimethylsilyl cyanide to (Z)-5-pentadecenal, under triethylamine catalysis, yielded... 

An important feature of the utility of bis(trimethylsilyl) hypophosphite in synthesis consists in its capability to undergo addition reactions, and which has been exploited in several ways to provide phosphinic acids which possess carboxy groups these reactions are summarized in Scheme 40 (the structures indicated here represent the final products following the acidolytic removal of trimethylsilyl groups). An equimolar mixture of phenylphosphonous dichloride (PhPCl2) and phenylphosphonous acid (phenylphosphinic acid) behaves as the phosphinic chloride 434, and so adds across carbonyl activated carbon-carbon multiple bonds by virtue of the presence of the P—H bond propenoyl chloride thus affords the acid dichloride 435, which may be hydrolysed to 3-(hydroxyphenylphos-phinoyl)propanoic acid (436). ... 

Dodd explored the metalation of 77-sulfonamidoindole-5-carboxamides [349]. Metalation at the 2-position was blocked by incorporation of a trimethylsilyl group (or by utilizing the corresponding indoline derivative). Treatment of protected... 

Alternative stereoselective methods to provide the above units were reported to utilize trimethylsilyl group as 116, which was produced from a silyl acetylene. Because of the A-strain effect the resulting product with MCPBA was only 117, from which silyl group was removed to give E epoxide 108, identical with that... 

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