Dimethylphenylsilyl group

The introduction of a (dialkylamino)dimethylsilyl or dimethylphenylsilyl group makes it possible to introduce a hydroxy group stereospecifically by Tamao oxidation78 80. This was successfully applied in the synthesis of /rrw.y-4-hydroxy-5-alkylfuranones81. 

Hydroboration of allylsilanes 1,2- or 1,3-diols.1 A dimethylphenylsilyl group can markedly affect the regiochemistry of hydroboration of an adjacent double... 

It is worthwhile mentioning that the dimethylphenylsilyl group can be substituted by a hydroxyl group with retention of configuration in two steps58 14 -> 15 (for a practical use of these silyl methodologies see references 59 and 140). 

In a related vein antenna chromophores have been developed for the self-sensitized photoreduction of ketones using isopropyl alcohol as a mild reducing agent189. One of the most effective chromophores for reduction of the model ketone 4-hydroxycyclohexanone was found to be the dimethylphenylsilyl group, as illustrated in equation 42. 

Parallel procedures for the oxidation of silyl groups to hydroxy groups were developed by Fleming and Tamao. The conversion of a dimethylphenylsilyl group, which involves a specific reaction mechanism, was pioneered by Fleming. 

Products 55 with a methyl group bonded to the sulfur have been tested as model compounds in the reaction with acylchlorides50 (Scheme 44). Also in these reactions the yields of enones 66 were higher in the case of the starting materials containing the trimethylsilyl group, than in the case of the dimethylphenylsilyl group. 

The relative stereochemistry of the a-bromoketone was not reported and is not of further interest as the bromine is removed later in the synthesis. But one can speculate that the bromine is transferred to the a-face of 24 and is arranged anti to the dimethylphenylsilyl group. 

In the laboratory of F.G. West, the stereoselective silyl-directed [1,2]-Stevens rearrangement of ammonium ylides was investigated as a potential key step toward the enantioselective synthesis of various hydroxylated quinolizidines. The dimethylphenylsilyl group served as a surrogate for one of the hydroxyl groups in the product. The Fleming-Tamao oxidation was performed under Denmark s conditions to avoid oxidation of the tertiary amine to the corresponding A/-oxide, and the desired quinolizidine did was obtained in 81% yield. 

By replacing one of the methyl groups by a dimethylphenylsilyl substituent the first new C —C bond is formed regioselectively remote from the bulky silyl unit. The dimethylphenylsilyl group can be eliminated in the final step by protodesilylation74. 

A carbon-bound dimethylphenylsilyl group is inert to most reaction conditions. This makes it an ideal profunctionality for a hydroxyl group [27], i.e., a latent hydroxyl group [28, 29] (Scheme 7.9). 

Scheme 7.9 A dimethylphenylsilyl group as a latent hydroxy function...

Structure and Properties of the Reagent. Low-temperature Si, C, and H NMR spectroscopic techniques have been used to probe the nature of these higher-order cuprates. These studies showed conclusively the facile dissociation-reassociation of ligands on copper. In the presence of methyllithium, dimethylphenylsilyllithium, and copper(I) cyanide, a mixed metallocuprate is formed (eq 2). The metallocuprate (2) preferentially transfers the dimethylphenylsilyl group to enones and 1-alkynes. 

Conjugate Additions to Enones. Reagent (1) effectively adds the dimethylphenylsilyl group to a,/8-unsaturated ketones, esters. 

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