Trimethylsilanolate potassium

To mention a few synthetic appHcations of trialkylsilanols, trimethylsilanol 4 adds readily to 2-chloroacrylonitrile in diethyl ether in the presence of triethylamine as triethylammonium trimethylsilanolate followed by ehmination of triethylamine hydrochloride to give 99 [32] (cf. discussion of the strongly nucleophihc properties of ammonium trimethylsilanolate 155 in Section 4.2.1). The stable potassium trimethylsilanolate 97 has also been used for the saponification of esters (Section 4.7). Dimethylphenylsilanol 100 adds readily to a,y9-unsaturated carbonyl compounds such as methyl vinyl ketone 764 in the presence of Pd(OAc)2 in a Heck-Suzuki-type reaction to give the sihcon-free /9-phenylmethylvinylketone 101 [33]. 

In the first total synthesis of thromboxane A2, lactone 340 is opened by potassium trimethylsilanolate 97 to give the potassium salt 341 [120]. The potassium salt of the methoxymethyl ether of salicylic acid is prepared likewise [121], as are... 

Methyl 4-chlorobenzoate (13.65 g, SOmmol) was added in one portion to a stirred slurry of potassium trimethylsilanolate 97 (10.26 g, 80 mmol) in 500 mb dry ether at ambient temperature, under N2. After 4h the white slurry is filtered under N2, washed with ether, and dried under a stream of N2 to afford 13.1 g (84%) analytically pure potassium 4-chlorobenzoate [119] (Scheme 4.62). 

When epoxides such as tra s-3-hexene-epoxide 1885 are heated to 65 °C with hexamethyidisiiane 857 and potassium methoxide in anhydrous HMPA, trimethylsilyl potassium 1882 is generated in situ to open the epoxide rings and give 1886, which subsequently looses potassium trimethylsilanolate 97 to afford olefins with inverted stereochemistry, for example as cis-3-hexene 1887, in high yield [103]. The reaction also proceeds at 65 °C in THF, rather than HMPA, if 18-crown-6 is added [103a] (Scheme 12.29). 

Materials. Methyl methacrylate was a product of Rohm and Haas, and t-butyl methacrylate was obtained from Polvsciences, Inc. Potassium trimethylsilanolate (PTMS) was obtained from Petrarch Systems, Inc. Anhydrous lithium iodide, trimethylsilyl iodide (TMSI), and n-butyllit.ium (in hexanes) were purchased from Aldrich Chemical Co. 

Two alternatives to conventional acid/base hydrolyses for cleaving esters are Sn2 displacement of the carboxylate group by reactive nucleophiles and nucleophilic attack at the carbonyl carbon. In this latter context we investigated the reaction of S-b-MM with potassium trimethylsilanolate, a so-called potassium superoxide equivalent (15). One advantage that this reagent has over potassium... 

We also explored the direct conversion of S-b-tBM to S-b-MA.K. Hydrolysis under basic conditions (KOH in refluxing aqueous THF) was again resulted in unchanged S-b-tBM. The reaction with potassium trimethylsilanolate for 1 hr in refluxing toluene gave very little reaction. Only 10% of the expected amount of potassium was found by ICP, and the NMR and IR spectra were little changed from those of the starting copolymer. This difference in reactivity between S-b-MM and S-b-tBM parallels that observed for the reaction of alkyl methacrylate blocks with potassium superoxide (7-10). 

In summary, we have examined several new methods for cleaving ester groups in poly(styrene-b-alkyl methacrylates). Short blocks of methyl methacrylate are very difficult to hydrolyze, but can be cleaved with reagents such as lithium iodide and potassium trimethylsilanolate. These latter reagents, however, result in side-reactions which appear to crosslink the polymer. 

Potassium trimethylsilanolate induced the cleavage of l,3-oxazolidin-2- and 5-ones affording the corresponding P-amino alcohols and amino acids. A A-benzoyl group was shown to be stable to this reagent, while a benzyloxycarbonyl group was easily removed <030B1106>. 

Work performed in our laboratory over the last several years has systematically addressed many of the problems associated with the thiocyanate chemistry. The use of sodium or potassium trimethylsilanolate for the cleavage reaction provided a method for rapid and specific hydrolysis of the derivatized C-terminal amino acid, which left the shortened peptide with a free C-terminal carboxylate ready for continued rounds of sequencing (3). The use of diphenylphosphoroisothiocyanatidate (DPP-ITC) and pyridine combined the activation and derivatization steps and... 

The chemical scheme for C-terminal sequencing is shown in Figure 2. The first step involves treatment of the peptide or protein sample with diisopropylethylamine in order to convert the C-terminal carboxylic acid into a carboxylate salt. Derivatization of the C-terminal amino acid to a thiohydantoin is accomplished with diphenylisothiocyanatidate (liquid phase) and pyridine (gas phase). The peptide is then extensively washed with ethyl acetate and acetonitrile to remove reaction by-products. The peptide is then treated briefly with gas phase trifluoroacetic acid, followed by water vapor in case the C-terminal residue is a proline (this treatment has no effect on residues which are not proline). The derivatized amino acid is then specifically cleaved with sodium or potassium trimethylsilanolate to generate a shortened peptide or protein which is ready for continued sequencing. In the case of a C-terminal proline which was already removed by water vapor, the silanolate treatment merely converts the C-terminal carboxylic acid group on the shortened peptide to a carboxylate. The thiohydantoin amino acid is then quantitated and identified by reverse-phase HPLC. 

To a stirred solution containing 650 mg (5.0 mmol) of potassium trimethylsilanolate in 100 mL of anhydrous ether was added, in one portion, 800 mg (3.0 mmol) of methyl... 

Scheme 2, Reaction of the siloxysilane 4 with potassium trimethylsilanolate.

The observed reaction products of the reactions of 4 with sodium and potassium trimethylsilanolates show the course of several competitive reactions with splitting of Si-O as well as Si-H bonds. In contrast to (Me3SiO)3SiH (4) the siloxysilane (Et3SiO)3SiH (5) reacts with KOSiMe3 only under Si-0 bond splitting (Eq. 7), presumably due to steric reasons. 

Poly-28 obtained by anionic polymerization of structure 28 and initiated with potassium or cesium alcoholates and/or potassium trimethylsilanolate had a linear structure. 

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