Trimethylsilyl o-

Quinazoline-2,4( 1 H,3H)-dione, 7-nitro-synthesis, 3, 110 Quinazolihediones mass spectra, 2, 22 polymers, 1, 298 Quinazoline-2,4( 1 H,3 H)-diones synthesis, 3, 106 O-trimethylsilylation, 3, 91 Quiriazolines addition reactions, 3, 73... 

O-Trimethylsilyl-S-alkyl, 344 O-Alkyl-S-alkyl or -S-phenyl, 345 0-Methyl-S-2-(methylthio)ethyl, 346... 

O-Trimethylsilyl-5-alkyl Acetals and Ketals R2C(SR )OSiMe3 Formation... 

The 0,N-dideuterated enol was formed by hydrolysis of the O-trimethylsilyl ether 123 (R = TMS) (in 80% [D6]DMSO/20% D2O with 5. lO " M DCl). N-Methylindoxyl (formed by hydrolysis of its acetate) exists in the solid state as a mixture of the enol and the keto tautomers (34% enol/66% keto). The NMR spectrum of freshly prepared solution in DMSO demonstrated signals of both enol and keto forms. However, at equilibrium (reached in 18 h at RT) the ratio of enol to ketone depends strongly on the polarity of the solvent used thus, in [Dg]DMSO the tautomeric mixture contains 92% enol, while in CDCI3 the keto form predominates (97%). A solution with 100% enol could be generated by hydrolysis of its O-trimethylsilyl ether [conditions 80% [Dfi]DMSO/20% D2O with 5 10" M DCl at 32°C (86TL3275 87PAC1577 88TL250)]. 

Structural Identification of Isomeric O-Trimethylsilyl Derivatives of Some Hexuronic Acids, J. F. Kennedy, S. M. Robertson, and M. Stacey, Carbohydr. Res., 57 (1977) 205-214. 

Partial Mass Spectra of Per-O-trimethylsilylated Dihexulose Dianhydrides83... 

X-ray diffraction pattern, 334-335 Mass spectra, partial, per-O-trimethylsilylated dihexulose dianhydrides, 253 meso forms... 

Per-O-methyl derivatives, acid hydrolysis, 232 Per-O-trimethylsilylated dihexulose... 

The addition of HCN to aldehydes or ketones produces cyanohydrins. This is an equilibrium reaction. For aldehydes and aliphatic ketones the equilibrium lies to the right therefore the reaction is quite feasible, except with sterically hindered ketones such as diisopropyl ketone. However, ketones ArCOR give poor yields, and the reaction cannot be carried out with ArCOAr since the equilibrium lies too far to the left. With aromatic aldehydes the benzoin condensation (16-54) competes. With oc,p-unsaturated aldehydes and ketones, 1,4 addition competes (15-33). Ketones of low reactivity, such as ArCOR, can be converted to cyanohydrins by treatment with diethylaluminum cyanide (Et2AlCN see OS VI, 307) or, indirectly, with cyanotrimethylsilane (MesSiCN) in the presence of a Lewis acid or base, followed by hydrolysis of the resulting O-trimethylsilyl cyanohydrin (52). The use of chiral additives in this latter reaction leads to cyanohydrins with good asymmetric... 

Finally, it should be emphasized here that some silylated intermediates, for example the subsequently described O-trimethylsilylated succinimide 202 a of silylated succinimide 201, are apparently silylated at higher temperatures to the very air-sensitive 0,0-bis(trimethylsilyl)sucdnimides (or 2,5-bis(trimethylsilyloxy)pyrroles)... 

The condensation of arylsulfonyl acetonitriles 369a-c with 22a proceeds via addition of the in-situ formed anion 370 to the arylsulfonyl acetonitriles 369 to afford the dimers 371, in 69-94% yield, and hexamethyldisiloxane 7 [136]. Furthermore, y9-dicarbonyl compounds such as ethyl acetoacetate 372 a or ethyl benzoyl-acetate 372b are O-silylated by 22 a or 22 c to rather stable alkyl 3-O-trimethylsilyl-oxycrotonoate 373a and alkyl 3-0-trimethylsilyloxy-3-phenyl acrylate 373b [130]. Aliphatic nitro compounds such as nitromethane are O-trimethylsilylated and further transformed into oligomers [132] (cf Section 7.6) and are thus unsuitable reactants for silylation-C-substitutions (Scheme 4.50). 

In a related reaction N-trimethylsilylpyrrolidone 388 a, which is assumed to be in equilibrium with the O-trimethylsilyl form 389 a, reacts with methyl-, butyl-, or... 

Whereas aldehydes such as benzaldehyde or ketones are converted by trimethyl-silylated alkyl- or aryl-mercaptans such as 575, in the presence of catalytic amounts of cyanide, to give high yields to O-trimethylsilyl-hemithioketals such as... 

Methyl levulinate 679 condenses with silylated y9-alanine 680 in the presence of catalytic amounts of TsOH-H20 to give hexamethyldisiloxane 7 and the Schiff-base 681, whose O-trimethylsilyl groups are saponified by water (derived from TsOH H2O) to give, via 682, the intermediate enamine 683. Subsequent condensation of 683 with the Schiff base 681 affords, via 684, and subsequent saponification, a 4 1 mixture of olefins 685 and 686 [201, 202] (Scheme 5.64). 

Nitrobenzene reacts with the O-trimethylsilyl ketene acetal 663 in the presence of tris(dimethylamino)sulfur(trimefhylsilyl)difluoride (Me2N)3S(Me3SiF2) (TASF) to give the O-silylated adduct 1007 a, which can be oxidized in situ, e. g. by bromine, to give the 4-substituted nitrobenzene 1008 in an overall yield of 79% [87] (Scheme 7.28). With less hindered ketene-acetals, however, mixtures of ortho- and para-substituted nitrobenzenes are obtained. Yet, on reaction of 4-fluoronitroben-zene with the cyclic O-trimethylsilyl ketene acetal 1009 the ortho-substitution product 1010 is obtained in 79% yield [87]. 

The unsaturated Oppolzer amide 1072 adds O-trimethylsilyl nitronates 1073 to give a 9 1 mixture of isoxazolines 1074 and 1075 in 96% yield [123, 124] (Scheme 7.41). 

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). 

O-Trimethylsilyl nitronates 1036 have been used in fluoride-catalyzed aldol-type condensations with aldehydes and ketones to give a-trimethylsilyloxy-nitro com-... 

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