Trimethylsilyl chromates

In an alternative oxidation, addition of chromium trioxide to hexamethyldisilox-ane (HMDSO) 7 gives bis(trimethylsilyl)chromate 2065, which is stabilized by addition of Si02 and which oxidizes primary or secondary alcohols such as 2066 or 2968, in CH2CI2, to their corresponding carbonyl compounds 2067 or 2069, in high yields [207] (Scheme 12.62). 

Bis(trimethylsilyl) chromate, 2591 Cadmium oxide, 3958 Caesium oxide, 4264... 

Bis(trimethylsilyl) chromate, 2591 Cadmium oxide, 3958 Caesium oxide, 4264 Caesium trioxide, 4263 Calcium oxide, 3937 Chromium(II) oxide, 4241 Chromium(III) oxide, 4251... 

Whereas the ester bis(trimethylsilyl) chromate is explosive and readily hydrolyzed,1398 the crystal structure1399 of the triphenyl derivative has been obtained (Table 112). The germanium, tin and lead analogues have been prepared by reactions (116) to (118). These compounds are... 

Montmorillonite K-10 supported bis(trimethylsilyl)chromate (0.93 g, equivalent to 1.5 mmol) was thoroughly mixed with 0.192 g benzyltetrahydropyranyl ether (1 mmol), and the material was placed in a beaker inside the microwave oven (900 W) for 20 s. After completion of the reaction as monitored by TLC (hex-ane-AcOEt, 8 2) the product was extracted into CH2CI2, the solvent was removed, and the residue was chromatographed on a silica gel column using hexane-AcOEt (8 2) to afford 92% benzaldehyde. 

Montmorillonite K-10 supported bis(trimethylsilyl)chromate (0.75 g, equivalent to 1.2 mmol of chromium(VI)) was mixed thoroughly with 1 mmol of semicarba-zone and irradiated by the microwaves (900 W). The progress of the reaction was monitored by TLC. After completion of the reaction, the solid phase was taken up in CH2C12, filtered, and washed with an excess of CH2C12. The filtrate was evaporated to dryness and purified by column chromatography using hexane-AcOEt, 8 2 as eluent to afford the corresponding carbonyl compound. 

Bis(trimethylsilyl) chromate, 2587 Cadmium oxide, 3952 Caesium oxide, 4258... 

Montmorillonite K-10, FejNOsjs, MW, 80-90% yield.Bis(trimethylsilyl) chromate "" and ammonium chlorochromate/Montmorillonite K-IO " as the oxidant gives similar results. 

Metal [258], metalloid [259], and nonmetal [260] -based oxidants are very efficient but rather toxic agents thus, vanadium oxytrichloride [258f], 2,6-dicarboxypyridinum chlorochromate (DCPCC) [258a], bis(trimethylsilyl) chromate (BTSC) [258e], chromic acid [261], and selenium... 

Oxidation. Reaction of chromic anhydride with HMDO in halogenated solvents leads to dissolution of the solid with formation of bis(trimethylsilyl)chromate (eq 14). 

Silica gel supported bis(trimethylsilyl) chromate in dry media also provided a fast, efficient and simple method for oxidation of alcohols to corresponding carbonyl compounds under microwave irradiation (Heravi et al., 1999). 

Bis (trimethylsilyl) chromate supported on silica gel can serve as an excellent oxidant for the oxidation of various types of alcohols under microwave irradiation without any solvent. This method decreases the time of reactions dramatically compared to ordinary condition. The products can be isolated by addition of dicho-romethane to the crude and filtration of reaction mixture. The high reactivity and selectivity of the supported reagent under microwave irradiation avoid the use of an excess of the oxidant, which may cause an overoxidation and other possible side reactions. 

Heravi et al. (1998) have reported direct oxidative deprotection of different trimeth-ylsilyl ethers to their corresponding carbonyl compounds with 75-92% yields using montmorillonite KIO supported bis(trimethylsilyl)chromate in dichloromethane. 

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