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Nitrile Oxides, Nitrones, and Nitronates in Organic Synthesis : Novel ...

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SILYLATION OF NITRO COMPOUNDS AS A PROCESS 703<br />

The reactions of most of known Nu (tertiary am<strong>in</strong>es, N-alkylated azoles, etc.)<br />

with BENA proceed through the pathway (a). This <strong>in</strong>terpretation is additionally<br />

conÞrmed by the fact that the reaction of N-methylimidazole with unsymmetrical<br />

BENA (434a) produces exclusively trimethylsilyl salt (512 ′′ ), whereas the<br />

pathway (b) would afford salt (512 ′ ).<br />

Earlier, another scheme was suggested for the generation of salts (513) based<br />

on oxim<strong>in</strong>o-alkylation of Nu with halo-oximes (504) (453). However, special<br />

experiments demonstrated that this reaction requires more severe conditions (536)<br />

<strong>and</strong> does not proceed dur<strong>in</strong>g the real generation of salts (513).<br />

A representative group of salts (513) was prepared (Scheme 3.267) by the<br />

reactions presented <strong>in</strong> Scheme 3.266.<br />

In addition to the salts shown <strong>in</strong> Scheme 3.267, several quaternary ammonium<br />

salts were detected by NMR spectroscopy among the products of the reactions of<br />

BENAs with DBU <strong>and</strong> HCONMe2. However, attempts to crystallize these salts<br />

failed, while other methods of puriÞcation of these products are lack<strong>in</strong>g.<br />

Pathway a: R1 =R2 =H; X=Cl,N-methylimidazole (80%), DMAP (49%), Et3N (54%).<br />

R1 =Me, R2 =H; X=Cl, N-methylimidazole (87%), DMAP (70%).<br />

R1 =H, R2 =Me; X=Cl, N-methylimidazole (60%).<br />

R1 =(CH2)2CO2Me, R2 =H; X=Cl, N-methylimidazole (94%),<br />

DMAP (84%), Et3N (72%).<br />

R1 =CO2Et, R2 =H; X=Cl, N-methylimidazole (54%).<br />

R1 =CO2Et, R2 =H; X=Br, Et3N (72%).<br />

R1 =Me, R2 =H; X=Cl, Me3N (72%).<br />

Pathway b: R1 =R2 =H; X=Cl, Pyrid<strong>in</strong>e (32%, impurities 504 <strong>and</strong> 514).<br />

R1 =R2 =H; X=OTf, Pyrid<strong>in</strong>e (60%, impurity 504).<br />

DMAP − N N<br />

MeO 2C<br />

The preparation of salts 513 with BENA (see Scheme 3,266)<br />

+<br />

N<br />

NOH<br />

− Cl<br />

513a<br />

NMe 2<br />

NaCN<br />

DMF, 70 ο C<br />

Scheme 3.267<br />

MeO 2C<br />

MeO 2C<br />

515<br />

NOH<br />

N O<br />

CN<br />

NH2<br />

79%

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