Amines formation from ketones

C. Secondary Reactions in Enamine Formation from Ketones and Amines. ... 

Conversion of crude chloro alcohol 47 to amino alcohol 48 was accomplished by dissolving 47 in a methanol/tcrt-butylamine mixture and heating to reflux (56 to 60°C) in the presence of 1 equiv of solid NaOH. The use of NaOH allows the rapid formation of intermediary epoxide 51, whose formation was confirmed by NMR and HPLC. Initially, with 1 1 MeOH/tert-butylamine, the displacement produced an 80 20 ratio of amino alcohols 48 52. Decreasing the amount of methanol led to reduced levels of the undesired regioisomer, with only 4% 52 being formed with a 1 5 ratio of MeOH/tcrt-butylamine. Further reduction in the amount of MeOH led to much slower reaction rates. After workup of the latter conditions, crystallization from heptane afforded an 89.8% isolated yield of amine 48 (from ketone 46) that was 99.9% pure with >99.9% ee as the (5)-enantiomer. 

Nucleophilic reactions. Chiral epoxides are converted into 2,2-dimethyl-l,3-dioxolanes with inversion of configuration by reaction with acetone. An efficient procedure for imine formation from ketones and amines specifies TiCU as promoter. Hydrolysis (or alcoholysis) of RCONH2 is achieved in the presence of TiCU in acidic media. 

Base Catalyzed Reactions. TMEDA can be monoprotonated (pATa 8.97) anddiprotonated (pATa 5.85). Titanium enolate formation from ketones and acid derivatives has been achieved by using Titanium(IV) Chloride and tertiary amines including TMEDA in dichloromethane at 0 °C. The reactive species, whieh is likely to be a complex with the tertiary amine, undergoes aldol reaction with aldehydes to form syn adducts with high stereoselectivity (eq 13). 

Unfortunately, addition of copper(II)nitrate to a solution of 4.42 in water did not result in the formation of a significant amount of complex, judging from the unchanged UV-vis absorption spectrum. Also after addition of Yb(OTf)3 or Eu(N03)3 no indications for coordination were observed. Apparently, formation of a six-membered chelate ring containing an amine and a ketone functionality is not feasible for these metal ions. Note that 4.13 features a similar arrangement and in aqueous solutions, likewise, does not coordinate significantly to all the Lewis acids that have been... 

In Robinson s now well-known suggestions, regarding the processes by which alkaloids may be produced in plants, two main reactions are used j the aldol condensation and the similar condensation of carbinol-amines, resulting from the combination of an aldehyde or ketone with ammonia or an amine, and containing the group. C(OH). N., with substances in which the group, CH. CO. is present. By these reactions it is possible to form the alkaloid skeleton, and the further necessary changes postulated include oxidations or reductions and elimination of water for the formation of an aromatic nucleus or of an ethylene derivative. 

This innovation was exploited by Stork and his co-workers (6-8) for a study of enamine formation from a variety of ketones and secondary amines. 

The intermediacy of an aminal in the formation of enamines from ketones and secondary amines is not usually proposed. The only direct evidence for this is the infrared spectra of the reaction mixtures produced when dimethyl-or diethylamine was allowed to react with cyclohexanone or cyclopentanone... 

Enamines derived from aldehydes can usually be obtained by the reaction of 2 equivalents of a secondary amine with the carbonyl compound, in the presence of anhydrous potassium carbonate, followed by pyrolytic distillation of the aminal with elimination of one of the amine groups (10,15, 30-36). Ketones are directly converted to enamines under the conditions of aminal formation. The azeotropic removal of water with excess aldehyde has also been described (32,37). 

While enamines can usually be obtained directly from ketones and secondary amines their formation by an indirect route may bo advantageous. The previously mentioned condensation of rnethyl ketones during azeotropic enamine formation has prompted the alklyation (J) or acylation and reduction (59) of Schiff s bases. A parallel method uses the formation and desulfurization of N-acylthiazolines followed by hydride reduetion (60,61). 

Hydrolysis of the new imine then allows formation of a ketone as part of an a-keto acid, and an amine which is the previously mentioned pyridoxamine 5 -phosphate. Since this imine is the product from an amine and a ketone, it is termed a ketimine. These reactions are reversible in nature, allowing amino acids to be converted into keto acids, and keto acids to be converted into amino acids (see Section 15.6). 

Figure 10-24 shows the reaction of a secondary amine with a ketone to form an encimine. With the exception of the last step, the mechanism for the formation of an enamine is similar to both the mechanism for the formation of a hemiacetal/acetal and the mechanism for the formation of an imine. In this case, because losing a hydrogen ion from a Ccirbon adjacent to the C=N carbon occurs more easily than a second attack, an enamine forms. The hydrogen loss is on the side that yields the more stable alkene. 

The mechanism of the aminolysis and the electronic effects of substituents at C-2 or C-4 on the kinetics of amide bond formation have been studied. In some cases, ring opening with amines occurs with partial isomerization of the exocyclic double bond. However, with more hindered compounds, such as unsaturated oxazolones derived from ketones, ring opening is stereospecific.Ring opening using diamines has also been described. Selected examples of dehydroamino acid amides prepared by aminolysis of unsaturated 5(4//)-oxazolones are shown in Table 7.40 (Fig. 7.51). 

Assuming that the above rationale for tertiary amine nitrosation was valid, we predicted 3) that the reaction of secondary amines with nitrite at milder pH s should be catalyzed by electrophilic carbonyl compounds, since secondary amines are known to form immonium ions on admixture with appropriate aldehydes and ketones. The prediction turned out to be true. Formaldehyde was shown to promote nitrosamine formation from a... 

Schiff bases having two nitrogen atoms as donors may be derived either from condensation of dialdehydes and diketones with two molecules of an amine, or from reaction of diamines with aldehydes or ketones. In Section 20.1.2.1, it has been pointed out that coordination through the N atom may occur only under particular circumstances. However, in the case of diimines the formation of chelate rings stabilizes the metal-nitrogen bond. Thus, they can form both mono-41 and bis-chelate42 complexes. 

As a supporting evidence, it is well-known that the electron-rich 0 6-arene)Ru complex of terminal alkyne 428 rearranges easily by the treatment with NaPR, of the )/ -vinylidenc complex 429, which is a strongly electrophilic carbene complex. Attack of ROH on the carbene carbon generates the the alkoxycarbene complex 431 via 430 [166]. Formation of ketone 427 by attack of the allylic alcohol is understanable by this mechanism. Formation of Ru-vinylidene complex 429 from the terminal alkyne has been proposed as the intermediate 432 of the reaction of terminal alkyne, amine and CO2 to form the vinyl carbamate 433 [167,168]. 

Asinger s studies demonstrated that product formation is sensitive to the ratio of sulfur to ketone (1), the structure of the ketone, the replacement of ammonia by amines, the temperature and the medium. Room temperature (20-25 °C) reactions in which the ratio of sulfur to ketones is 0.5 favors the formation of 3-thiazoline, 2, as shown in Figure 1. The formation of 5-alkylidene-3-thiazolines, 3, sometimes competes with the formation of 3-thiazolines such is the case when aryl ketones such as l-phenylpropan-2-one and l-phenylbutan-2-one are employed (4). Also the additional presence of hydrogen sulfide promotes the generation of 1,2,4-trithiolanes and 1,2,4,5-tetrathiolanes from ketones ana aldehydes at the expense of 3-thiazoline formation (11-12). Increasing the S/ketone ratio to 8 favors the formation of the 3-imidazoline-5-thione (5), a product which has a greater tendency to result from aryl methyl ketones (3). 

The products obtained in the nitrous acid deamination of amine 117 in acetic acid are shown in Scheme 10 (Nishimura et ol., 1967, 1970). Nitrogen loss occurs from a primary saturated carbon atom and this case is therefore not strictly pertinent to this section. To account for the formation of ketone 118 among the reaction products the authors... 

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