Oximes trimethylsilylation

Gas Chromatographic Estimation of Urinary Vanillylmandelic Acid After Transformation to Vanillin Meth-oxime Trimethylsilyl Ether Clin. Chim. Acta 26(2) 307-311 (1969) CA 71 120323V... 

The simultaneous g.c. analysis of sugars (Ara, Rha. Fiu, Gal, Glc, sucrose, maltose and raffinosc), sorbitol, and nine organic acids in vegetables and strawberries utilized derivatives produced by oximation - trimethylsilylation."... 

Lawson, A.M., Chalmers, R.A. and Watts, R.W.E. (1974b), Studies of O-substituted oxime-trimethylsilyl ester derivatives of some metabolically important oxocarboxylic acid,s. Biomed. Mass Spectrom.y 1,199. 

R = Me, R = H) with cyclohexenol in the presence of F ion followed by NaOCl oxidation gave the tricyclic ether 61 in 65% yield (Scheme 9) [29]. The use of propargyl alcohol and propargyl thiol led, via the acetylenic oximes, to fused tetrahydrofuranoisoxazoles 62 a and 62 b, and tetrahydrothiopheno[3,4-c]isoxa-zole 62 c, respectively. Reaction of l-butyn-4-ol with 0-trimethylsilyl a-bro-moaldoxime 52e (R = R = Me) led to the tetrahydropyranoisoxazole 62 d. 

The oxime 299 is silylated in the presence of catalytic amounts of TMSOTf 20 to 300, which affords, via the Beckmann fragmentation intermediate 301 and alkylation with allyltrimethylsilane 82, 66% of the seco nitrile 302 [101, 102] (Scheme 4.39). Tris(trimethylsilyl) ketenimine 303 reacts with aldehydes such as benzaldehyde in the presence of Bp3-OEt2, via the aldol adduct 304, to give the unsaturated nitriles 305, in 99% yield, and HMDSO 7 [103]. 

If an electron-attracting group is present in the position yS to the nitro moiety, formation of trimethylsilyl nitronates from, for example 1050, leads, via 1051, to the oximes 1052 in 73-78% yield [106]. Subsequent transsilylations of 1052 with methanol give the free oximes in high yield [106] (Scheme 7.36). 

Methyl 4-nitrobutyrate 1099, on treatment with Me3SiBr 16/NEt3, affords the unsaturated O-trimethylsilylated oxime 1101, in 71% yield, via the O-trimethylsilyl nitronate 1100 and elimination of trimethylsilanol 7 [107, 131] whereas the nitro compound 1102 is converted by TCS 14/NEt3, via 1103, into the / -chlorooxime 1104, in 39% yield [107] (Scheme 7.45). 

Other compounds identified in caramels are di-D-fructose and poly(glycosyl) dianhydrides (DFAs). DFAs were found in caramels prepared from D-fructose, D-glucose, and sucrose. The analysis was done after derivatization as TMS (per-0-trimethylsilyl) derivatives or as TMS-oxime (per-O-trimethylsilyl oxime) by... 

N, C -Coupling reaction of BENA with trimethylsilyl azide is the key step of a very convenient and versatile procedure for the synthesis of otherwise difficultly accessible a-azido oximes (524, 525) (Scheme 3.248). 

Structures of four derivatives of pregnenolone employed in GC/MS in (a) the 3-heptafluorobutyrate, in (b) the 3-trimethylsilyl ether 20-pentafluorobenzyloxime, in (c) the 3-trimethylsilyl ether 20-pentaf1uorobenzylcarbox-ymethoxime, and in (d) the 20-oxime... 

O-Substituted oxime derivatives are synthetically useful in a wide variety of transformations. Hoffman and Butani have observed that reaction of a series of aldehydes and ketones with the potassium salt of Af,0-bis(trimethylsilyl)hydroxylamine 4a or 4b (a rapid equilibrium between 4a and its Af,N-bis(silylated) isomer 4b probably exists in solution) gave high yields of the corresponding oximate anion 5, formed via the Peterson-type reaction, together with the silyl ether 6. Anion 5 could be protonated to the oxime 7 or trapped in situ with a variety of electrophiles to give 0-substituted oxime derivatives (Scheme 6). 

In this context, Yadav and coworkers have recently developed a mild and efficient procednre for the selective rednction of / -nitrostyrenes 22 to oximes 23 using indium metal in aqueous methanol under neutral reaction conditions (Scheme 19). Similarly, a-alkoxy oximes 24 are formed in good yields by the treatment of nitroolefins with metalhc indium and trimethylsilyl chloride in anhydrous methanol (Scheme 19). 

Hajipour and coworkers prepared benzyltriphenylphosphonium peroxymonosulfate (BnPhsPHSOs) in a very high yield (95%) and purity (99%). This new oxidizing reagent was applied successfully in various deprotection reactions such as the conversion of oximes, phenylhydrazones, 2,4-dinitrophenylhydrazones and semicarbazones to the corresponding carbonyl compounds in the presence of bismuth chloride under nonaqueous conditions . Oxidative deprotection of trimethylsilyl ethers, tetrahydropyranyl ethers and ethylene acetals with BnPh3PHS05 under microwave irradiation affords the corresponding carbonyl compounds in very high yields (equation 71). The same reaction also proceeds under nonaqueous conditions ". 

Mason and Slover187 studied the separation of monosaccharides as the O-trimethylsilyl derivatives of the oximes, as an alternative method to analyzing for sugars in foods, and Clayton and H.G. Jones188 used trimethylsilylated D-glucose oxime. Both groups of workers referred to the instability of these derivatives, as noted in Section III (see p. 23). Laine and Sweeley189 proposed a similar method that used the methoxime derivatives. 

Trimethylsilyl polyphosphate (PPSE),1 The reagent is prepared from P205 and [(CHj),Si]20. It is a colorless, volatile liquid, soluble in the usual organic solvents. It is comparable to polyphosphate ester for the Beckmann rearrangement of oximes to amides (3, 230 231). but it is prepared more easily. 

Potassium hydroxide, 258 Trimethylsilyl chlorochromate, 327 of carbon-carbon double bonds substituted by heteroatoms m-Chloroperbenzoic acid, 76 of oximes to carbonyl compounds Lithium aluminum hydride-Hexa-methylphosphoric triamide, 159 Titanium(III) chloride-Diisobutylalu-minum hydride, 303 Trimethylsilyl chlorochromate, 327 of protected alcohols Chlorodimethylthexylsilane, 74 Formic acid, 137 p-Methoxyphenol, 181 of thioacetals and -ketals Methoxy(phenylthio)trimethyl-silylmethane, 182... 

A wide range of organic azides such as alkyl,80 alkenyl,79,100 aryl, including dinitrophenyl and picryl,101-103 heterocyclic,28,91 trimethylsilyl,79,104 acyl,9 phosphoryl,105 sulfonyl,106 alkoxycarbonyl,9 and oxime azides107 has been found to add to norbornene,25,79,90,104,105,107-121 its derivatives,104 106,1 13,120,122-128 or to related bridged bicyclic... 

Nitrosonium ion can also act as a mild and selective oxidizing agent. It has been used to cleave oxidatively oximes, hydrazones,498 and thioketals to their corresponding carbonyl compounds,499 to cleave benzylic esters515 [Eq. (5.195)], and to oxidize O-tributylstannyl and (9-trimethylsilyl ethers and benzylic alcohols516 [Eq. (5.196)]. 

Figure 5.1. Derivatization of glucose for GC-MS analysis. Aldehyde and keto groups are converted into oximes using methoxyamine, followed by conversion of hydroxyl groups into trimethylsilyl (TMS) groups. This example depicts the derivatization of two tautomeric forms, syn and anti, formed during rotation along the C=N bond.

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