Dehydration, of oximes

The creation of the N—N bond as the last step of the ring synthesis is common in indazoles and very rare in pyrazoles. In indazoles this method is well known (type B synthesis (67HC(22)l), for example, the dehydration of oximes (570) with acetic anhydride yields 1-acetylindazoles (571), and in basic medium the indazole 1-oxides (573) are formed from the nitro derivatives (572). 

Indirect conversion of niiro compounds into nitnles via dehydration of oximes fsee Section 6.3.3 is also a useful method for this purpose. 

Dehydration of oximes to form nitriles is, again, a rare but intriguing reaction. It has, indeed, been demonstrated that cytochrome P450 (see Chapt. 3 in [50]) is able to transform butanal oxime (11.103, R = H, R = Pr, Fig. 11.14, also 11.72) to butanenitrile by a Beckmann-type dehydration [105] [133]. The reaction is inhibited by the presence of 02, and is catalyzed by cytochrome P450 in its reduced (ferrous) state. 

Thiocarbonate esters, obtained from aryl chlorothionoformates and hydroxyl groups, react similarly [206, 207]. This reaction was also used for the dehydration of oximes [208]. 

Dehydration. This reagent is useful for synthesis of acyl azides from carboxylic acids, NaCN, and pyridine, with tetrabutylammomum bromide as catalyst (75-95% yield). In combination with pyridine, it effects dehydration of oximes to nitriles in 80-90% yield, P-Lactams can be prepared directly in 40-75 )t yield from carboxylic acids and imines with the reagent (1 equiv,) and triethylamine (excess). In general, a mixture of cis- and rra/j5-azetidinones is formed. 

Dehydration.1 This reagent is useful for synthesis of acyl azides from carboxylic acids, NaCN, and pyridine, with tetrabutylammonium bromide as catalyst (75-95% yield). In combination with pyridine, it effects dehydration of oximes to nitriles in 80-90% yield. 

Miller, C. P., Kaufman, D. H. Mild and efficient dehydration of oximes to nitriles mediated by the Burgess reagent. Synlett 2000,1169-1171. 

Dehydration of oximes to nitriles with the reagent also has been reported. A solution of 0.05 mole of heptaldoxime and 5 drops of triethylamine in 30 ml. of benzene was treated with 0.1 mole of phenyl isocyanate in 10 ml. of benzene and lefluxed for 2 hrs. The carbon dioxide evolved was collected as BaCOs and cor-... 

Dehydration reactions using the tertiary phosphine-carbon tetrachloride adduct have appeared quite regularly in the literature again this year. Among those reported have been the dehydrations of oximes to nitriles, carboxylic acids to anhydrides, and the amides (37) to the cumulenes (38). Further reaction of the dehydration product from treatment of the... 

Pyrrole and indole carbonitriles are readily prepared by dehydration of oximes. Because the aldehydes are easily available by Vilsmeier-Haack formylation, this represcarboxylic acid derivatives <80CJC409,88SC67l,93JMC10l>. 

Dehydration of Oximes. Tosyl chloride was used for the conversion of aromatic aldoximes to nitriles under microwave irradiation as shown in eq 51. The reagents were adsorbed on... 

Wan and coworkers reported a rhodium-catalyzed [2 -I- 2 + 2] cycloaddition of oximes and diynes for the synthesis of pyridines in 2013 [45]. In their mechanistic study, they exclude the dehydration of oxime to generate the corresponding nitrile followed by the cycloaddition of the nitrile and the alkynes to afford the pyridine as the pathway. As only a trace amount of benzonitrile was produced from oxime under the reaetion conditions. Additionally, pyridine product was detected in less than 20% yield when benzonitrile was subjected to the reaetion with diyne instead of oxime (Scheme 3.19). EtOh was tested as solvent here as well, but not produeed. Later on, they found that by using Rh (NBD)2BF4/MeO-Biphep as the eatalyst system, the reaction can be performed in EtOH [46]. 

Oxyma [59, ethyl 2-cyano-2-(hydroxyimino)acetate] has been 0-sulfonated, and the sulfonate ester (60) is an excellent catalyst for dehydration of oximes to nitriles. ... 

The following reagents may also be used for dehydration of oximes to... 

Sardarian, A.R., Z. Shahsavari-Fard, H.R. Shahsavari, and Z. Ebrahimi. 2007. Efficient Beckmann rearrangement and dehydration of oximes via phosphonate intermediates. Tetrahedron 48 (14) 2639-2643. 

The convenient formation of nitriles by dehydration of oximes using FVP over molecular sieves has been appHed to the synthesis of pyrrole-3-carbonitrile 43 and indole-3-carbonitrile 44 (Scheme 8 2015UP9). 

The efficient fonnation of nitriles by dehydration of oximes using FVP over molecular sieves has been applied to the synthesis of thiophene-3-carboni-trile 183 (Scheme 37 2015UP9). FVP of the acid chloride 184 at 850 °C results in a loss of HCl to produce the heterocycHc phenanthrol analog 185 in a moderate yield (2015UP10). The benzofuranthiones 186 undergo quantitative isomerization to the benzothiophenones 187 on pyrolysis at 850 °C (2006HCA991). 

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