Imine products

Write the structure of the carbinolamine intermediate and the imine product formed in the reaction of each of the following... 

The carbinolamine is formed by nucleophilic addition of the amine to the carbonyl group Its dehydration gives the imine product... 

Loss of H+ from nitrogen then gives the neutral imine product. 

Reaction of an aldehyde or ketone with a secondary amine, R2NH, rather than a primary amine yields an enamine. The process is identical to imine formation up to the iminium ion stage, but at this point there is no proton on nitrogen that can be lost to form a neutral imine product. Instead, a proton is lost from the neighboring carbon (the a carbon), yielding an enamine (Figure 19.10). 

Vasudevan et al. have reported a microwave-promoted hydroami-nation of alkynes. Heating a mixture of l-ethynyl-4-methoxybenzene and 4-bromoaniline in water at 200°C in a microwave reactor for 20 minutes without any catalyst gave an imine product in 87% yield (Eq. 4.45).81... 

The corresponding imine products undergo a wide range of reactions to form various synthetically and biologically important products (discussed in the following). 

The catalytic activity of MAO can be simply characterized as two half-reactions (Fig. 4.33). In the first half-reaction, the amine substrate is oxidized and the FAD cofactor is reduced. In the second half-reaction, the imine product is released and the FAD cofactor reoxidized generating peroxide. The released imine chemically hydrolyzes to the corresponding aldehyde. 

FIGURE 4.33 Reactions (A) and (B) describe the MAO catalytic cycle while reaction (C) describes the subsequent aminolysis of the MAO-produced imine product to the aldehyde. 

A modification of the Pomeranz-Fritsch synthesis <1983JCXI3344> is used in the preparation of thieno[2,3- l-pyridine and its 2-substituted derivatives. An aryl aldehyde undergoes condensation with aminoacetaldehyde dimethyl acetal giving a Schiff base which cyclizes to form an imine product. The imine is treated with ethyl chloroformate followed by triethyl phosphate to form an intermediate carbonate-phosphonate, which then cyclizes to the thienopyr-idine product (Scheme 22) <2004S1935>. Very low product yields (2-17%) are obtained for alkyl- and phenyl-substituted thieno[2,3- ]pyridines however, the unsubstituted product and 2-halogenated derivatives give moderate yields (28-44%). 

In fact, rearrangements of singlet alkylnitrenes generated in frozen matrices cannot even be suppressed by developing strain in imine products such as 1-3, although some triplet nitrene is detected by EPR and UV-vis spectroscopy upon low-temperature photolysis of 1-azidonorbornane. ... 

The initial success with early transition metals, such as zirconium and titanium, reported by the Buchwald group, included an indirect cycloaddition between an enyne and isocyanides. The first protocol that used [Gp2Ti(PMc3)2] or Ni(GOD) together with triphenylphosphine failed to cyclize the enynes under the pressure of GO, but provided the cyclic imines with trialkylsilyl isocyanides, and bicyclic enones were obtained by hydrolysis of the resultant imine products (Equation (9)). ... 

Aliphatic and aromatic aldehydes condense with aliphatic and aromatic primary amines to form JV-substituted imines. The reaction is catalyzed by acids and is generally carried out by refluxing the amine and the carbonyl compound with an azeotroping agent in order to separate the water formed. The aliphatic imines (C5-C10) are obtained in good yield but are unstable and must be used directly after their distillation [2b], Tertiary aliphatic and aromatic aldehydes at room temperature react readily and nearly quantitatively with amines to give the imines without the aid of catalysts [la]. Primary aliphatic aldehydes tend to give polymeric materials with amines as a result of the ease of their aldol condensation [3]. The use of low temperatures and potassium hydroxide favors the formation of the imine product [4a, b]. Secondary aliphatic aldehydes readily form imines with amines with little or no side reactions [5]. 

A Schiff base is the common name for the (usually acyclic) imine product of the reaction of a primary aryl amine with an aldehyde or ketone. These imines are stable if there is at least one aryl group on the imino nitrogen or on the imino carbon (54). A cyclidene is generically a cyclic, multidentate imine. 

The aldehyde or ketone (30 50 mL) was dissolved in benzene or toluene (30 50 mL) in a 100-150-mL round-bottomed flask equipped with a reflux condenser, a Dean Stark trap, and a magnetic stirring bar. Benzylamine (1 equiv) and TsOH - H20 (1 mol %) were added and the mixture was stirred at reflux. When the reaction was complete (theoretical amount of water removed monitored by GC, TLC. H and l FNMR), the solvent was removed under reduced pressure and the imine product 14 was purified by column chromatography. 

These are either ketimines or aldimines, according to whether the carbonyl compound is a ketone or an aldehyde. For R= H, the imine product generally is unstable and polymerizes. Usually these derivatives are solids and are excellent for the isolation and characterization of aldehydes and ketones. 

The initial reactions of this type were used to produce copper(II) complexes of salicylaldimines, where additional coordination support is provided by the phenolic oxygen atoms (equation l).10 11 Similar use can be made of pyridine-2-carbaldehyde in the formation of imine chelates. For example, the combination of pyridine-2-carbaldehyde and 2-aminobenzenethiol in the presence of metal ions yields tridentate complexes (Scheme l).12 If the reaction is carried out in the absence of the metal ion, the benzothiazolidine (1) is isolated. Thus the metal ion is essential for the formation of the imine product in this case. Metal complexes of the related tridentate ligands (2),13 (3),14 (4)li and (5)16 can be prepared similarly. 

Figure 3.11 Representative examples of Fe(acac)3-catalyzed imination products.

The imine product shown exists as a tautomer with its corresponding enamine. 

Step 2b Acid workup gives the imine product which then undergoes hydrolysis to the corresponding aldehyde. 

A 265.2 g (1 mole) of pyridoxal-5-phosphate was slurried in 1 L of methanol, and 400 mL of 5 M NaOH was added. When the solution was homogeneous, 34.2 mL of 1,2-diaminoethane was added rapidly with vigorous stirring. The imine product sodium N,N -bis(pyridoxal-5-phosphate)ethylenediimine or sodium 5-(N-(3-hydroxy-2-methyl-5-phosphonomethyl-4-pyridyl) methylideneaminoethyleneiminomethyl)-2-hydroxy-3-methyl-5-pyridylmethylphosphate was stirred for 1 hr, 400 mL of diethyl ether was added, and the slurry was filtered. The filtrate was washed with 600 mL of... 

Complexes 132 and 133 reacted with a range of unsaturated substrates to afford [2 + 2] cycloaddition products. Addition of carbon dioxide to 133 gave complex 145 as adjudged by FTIR spectroscopy, mass spectrometry, and combustion analysis. Complexes 133 and 132 afforded complexes 146 and 147, respectively, after addition of adamantyl isocyanate. The formation of 146 and 147 is noteworthy from a regioselective point of view in that 1,2-addition gives the carbonyl-amide product. However, the alkoxide-imine product might have been expected given that the Lewis acidity of... 

---