And dehydration of oximes

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. 

Citral readily forms acetals by acid-catalyzed addition of alcohols or by the use of trialkoxyorthoformates. Citral dimethyl acetal [7549-37-3] is stable under alkaline conditions, whereas citral is not. Neryl and geranyl nitriles can be made by oximation of citral and dehydration of the intermediate oxime. For instance, geranonitrile [31983-27-4] is made as follows ... 

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). 

Addition of N2O3 to alkenes and dehydration of the intermediate nitro oximes 52 is another efficient pathway to furoxans (35JPR277, 73CJC2406, 74GEP(0) 2336403, 77BRP1474693, 91LA1211) (Scheme 21). 

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... 

RCH2.NO2 - RC=N. This conversion usually has been conducted via a Nef reaction to an aldehyde followed by formation and dehydration of an oxime. The transformation can be accomplished in one step by reaction of the primary nitro compound with PCI3 and pyridine (40-75% yield). This method can also be used to convert allylic nitro compounds into a,)3-unsaturated nitriles and to prepare aldehyde or ketone cyanohydrin acetates. 

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>. 

Various vinyl isocyanides 1521-1525 are prepared from oximes (for example, 1519) by reductive formylation and dehydration of the resulting vinyl formamides (for example, 1520) with phosgene in 40-97% yield [1167]. For the dehydration step, DABCO proved to be the most effective base among acid scavengers (EtsN, pyridine, and quinoline were also used). 

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 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 dehydration of oximes by such reagents as phosphorus pentoxide, thionyl chloride, acetic anhydride, acyl chlorides, and phosphorus pentachloride is well known [26]. In effect, this dehydration procedure permits the conversion of aldehydes to nitriles with the same number of carbon atoms. A modification applicable only to the aromatic series makes use of boiling acetic acid as a dehydrating agent [27]. With other dehydrating agents, aliphatic aldehydes also may be converted to nitriles. Oximes may be converted readily to nitriles by an acid-catalyzed reaction with ortho esters [28]. 

The formation of oximes, hydrazones, and related imine derivatives is usually catalyzed by both general acids and general bases. General base catalysis of dehydration of the tetrahedral intermediate involves nitrogen deprotonation concerted with elimination of hydroxide ion. ... 

The fi-compound is dissolved in 50 c c. pure dry ether, and dry hydiogen chloride is passed in with constant shaking to prevent the delivery tube from becoming blocked. Colourless crystals of the hydrochloride of the /3-o ime separate and aie filtered and washed with dry ether and then placed in a separating funnel and covered with a layer of ether. A. concentrated solution of sodium carbonate is gradually added with constant shaking until no further effervescence is observed. Sodium chloride is precipitated and the /3-oxime dissolves in the ether. The ether extract is sepaiated, dehydrated over sodium sulphate, and the ether remoi ed as rapidly as possible at the ordinary temperature by evaporation in vacuo. The residue crystallises, and when pressed on a porous plate leaves a mass of small silky needles, m. p. 126—130A It may be re-... 

When acetone is treated with hydroxylamine in aqueous solution near neutral pH, the carbonyl UV absorption intensity decreases very rapidly this fast spectral change is followed by a much slower absorption increase that is due to the appearance of the oxime product. This suggests that, at such pH values, the initial addition is very rapid and the second step, dehydration of the carbinolamine, is the rds. Figure 5-12 is a plot of the apparent first-order rate constant against pH for this reaction. As the pH is decreased from neutrality, the rate increases, indicating that the rds... 

Quinazoline 3-oxides were first prepared by Awers and von Meyen-burg in 1891 by the dehydration of o-acylamino benzophenone oximes with acetic acid-acetic anhydride and were assigned the in-dazole structure (33). This was then modified by Bischler to the... 

In a synthetic approach to acetylfurazans and their A-oxides, an oximation and dehydration or oxidation of 3-hydroximinopentan-2,3-dione resulted in the formation of the furazan ring [22G289, 37G388, 87JCS(P2)523] (Scheme 59). 

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