Amines rearrangements during

An n.m.r. spectrum of cyclobutylamine in carbon tetrachloride showed no resonance signals at less than 1 p.p.m. from tetramethylsilane. This suggests that no cyclopropylcarbinyl-amine was formed by rearrangement during the reaction. 

The rearrangement of unsymmetrical allylamines 9 was investigated to exclude any competing 1,3-rearrangement during the course of the reaction. Allyl vinyl amines 10 were generated via condensation starting from allylamine 9 and isobutyraldehyde 2. The substrates 10 were subjected to the acid-accel-... 

Scheme 2.8 Benzyne mechanism to account for rearrangement during amination of halobenzenes.

Similar to carboxamides, sulfonamides [229,230] and amidophosphates [230] may also be a-methoxylated at the anode. p-Tolysulfonamides of primary amines undergo a rearrangement during anodic oxidation in methanol in the presence of KBr and KOH, leading to a-amino aldehydes [231]. Bromide ion is involved as inorganic redox catalyst. 

N.S. Mani and co-workers utilized the organoaluminum promoted modified Beckmann rearrangement during their efficient synthetic route to chiral 4-alkyl-1,2,3,4-tetrahydroquinoline. (4R)-4-Ethyl-1,2,3,4-tetrahydroquinoline was obtained by rearrangement of the ketoxime sulfonate of (3R)-3-ethylindan-1-one. The resulting six-membered lactam product was reduced to the corresponding cyclic secondary amine with diisobutylaluminum hydride. 

Acylfurans 364 react with secondary amines (piperidine, pyrrohdine, morpholine, dibutylamine) in the presence of catalytic amounts of acids (AcOH, HCl) to give enamines 365, which rearrange during distillation into 2-aminophenols 366 (equation 174). 

The Curtius rearrangement can be catalyzed by Lewis acids or protic acids, but good yields are often obtained also without a catalyst. From reaction in an inert solvent (e.g. benzene, chloroform) in the absence of water, the isocyanate can be isolated, while in aqueous solution the amine is formed. Highly reactive acyl azides may suffer loss of nitrogen and rearrange already during preparation in aqueous solution. The isocyanate then cannot be isolated because it immediately reacts with water to yield the corresponding amine. 

Section A of Scheme 10.15 contains a number of examples of Curtius rearrangements. Entry 1 is an example carried out in a nonnucleophilic solvent, permitting isolation of the isocyanate. Entries 2 and 3 involve isolation of the amine after hydrolysis of the isocyanate. In Entry 2, the dihydrazide intermediate is isolated as a solid and diazotized in aqueous solution, from which the amine is isolated as the dihydrochloride. Entry 3 is an example of the mixed anhydride procedure (see p. 948). The first stage of the reaction is carried out in acetone and the thermolysis of the acyl azide is done in refluxing toluene. The crude isocyanate is then hydrolyzed in acidic water. Entry 4 is a reaction that demonstrates the retention of configuration during rearrangement. 

During the first month of this experiment, it was realized that this reaction is extremely variable. Thus, diverse amines (ammonia, primary and secondary amines, hydrazine derivatives, hydroxylamines) 13, carbonyl compounds (aldehydes, ketones) 14, acid components 15 or their anions (H2O, Na2S203, H2Se, R2NH, RHN-CN, HN3, HNCO, HNCS, RCO2H, RCOSH, ROCO2H, etc.), and the isocyanides could form the a-adducts 16 that rearrange into their products 17 (Scheme 1.5). 

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