Aldimines aldehydes

N-Benzenesulfonyl aldimines. Aldehydes are readily converted to a-tosyl sulfonamides by reaction with PhS02NH2, elimination of TsH is accomplished with NaHCOj. 

From nitriles by treatment with anhydrous Stannous chloride dissolved in ether saturated with hydrogen chloride the resulting crystaUine aldimine stannichloride, [(RCH=NHj)2] SnCl, or (RCH=NH,HCl)2SnCl4, is hydrolysed by warm water, and the aldehyde is isolated by distillation with steam or by extraction with a solvent (Stephen reaction), for example, for R = CH3(CH2)4, i.e., n-amyl ... 

Decant the ethereal solution from the yellow aldimine stannichloride which has separated, rinse the solid with two 50 ml. portions of ether, and transfer the solid to a 2-5 litre flask fitted for steam distillation and immersed in an oil bath at 110-120°. Pass steam through a trap (compare Fig. 11,40, 1,6) to remove condensed water, then through a superheater heated to 260° (Fig. I, 7, 2), and finally into the mixture (2). Continue the passage of y steam until the aldehyde is completely removed (4-5 litres 8-10 hours). Filter the white soUd at the pump, and dry in the air. The resulting p-naphthaldehyde, m.p. 53-54°, weighs 12 g. It may be further purified by distillation under diminished pressure (Fig. II, 19, ) -, pour the colourless distillate, b.p. 156-158°/15 mm., while hot into a mortar and powder it when cold. The m.p. is 57- 58°, and the recovery is over 90 per cent. 

Aldehydes, general procedure (3). A solution of nilnie 1 (1 mol) in EtOAc saturated with HO gas al 0°C is added to a solution ol SnCl2 (1.1 mol) in EtOAc previously saturated wlh HCI at 0°C. After several hours at 0°C the aldimine complex (R.CHNH2 3 SnCle separated as pale yellow prisms. The complex was filtered, washed with EtjO and dried over KOH under vacuum to afford a pure sample of 2. Steam distillation of 2 gave aldehyde 3 in the distlRate if the aldehyde was volatile. Alternatively, the aldehyde was extracted from the residue of the steam distillate... 

Several blocked diamines or amino-alcohols are commercially available. The aldimine is an aldehyde-blocked diamine. The ketimine is a ketone-blocked diamine. The oxazolidine is a five-membered ring containing oxygen and nitrogen. The oxazolidine ring shown below is an aldehyde-blocked amino alcohol. The basic synthetic concepts of an aldimine, a ketimine, and an oxazolidine are shown below ... 

Petrow described the formation of 3-iminoketones from 3-keto-aldehydes and aniline. Cyclization in the presence of aniline hydrochloride and ZnCh smoothly provides the desired quinoline 26. Bis-imine 24 is the proposed intermediate that undergoes cyclization. The aldimine is more reactive than the ketimine toward cyclization thus, cyclization on the aldimine occurs. When the bis-imine is not formed, partial aniline migration can occur which results in mixtures of cyclized products. 

We have previously discussed that keto-aldehydes react with anilines first at the aldehyde carbon to form the aldimine. Subsequent condensation with another aniline formed a bis-imine or enamino-imine. The aniline of the ketimine normally cyclizes on the aldimine (24 —> 26). Conversely, cyclization of the aldimine could be forced with minimal aniline migration to the ketimine using PPA (30 —> 31). The use of unsymmetrical ketones has not been thoroughly explored a few examples are cited below. One-pot enamine formation and cyclization occurred when aniline 48 was reacted with dione 49 in the presence of catalytic p-TsOH and heat. Imine formation occurred at the less-hindered ketone, and cyclization with attack on the reactive carbonyl was preferred. ... 

In general the reaction of an aldehyde with a ketone is synthetically useful. Even if both reactants can form an enol, the a-carbon of the ketone usually adds to the carbonyl group of the aldehyde. The opposite case—the addition of the a-carbon of an aldehyde to the carbonyl group of a ketone—can be achieved by the directed aldol reaction The general procedure is to convert one reactant into a preformed enol derivative or a related species, prior to the intended aldol reaction. For instance, an aldehyde may be converted into an aldimine 7, which can be deprotonated by lithium diisopropylamide (EDA) and then add to the carbonyl group of a ketone ... 

In contrast, aqueous ethanolic ammonia effects initial nucleophilic displacement of bromide, which is followed by ring closure of the benzylamine so-formed at the aldehyde group to give 5//-dibenz[f, f]azepines 48.85 The (1-bromoethyl) aldehyde 47 undergoes ring closure with benzylamine to give 6-benzyl-5-methyl-5//-dibenz[c t>]azepinium bromide (49, R = Me), whereas the (bromomethyl) aldehyde 45 yields a mixture of the quaternary salt 50 and the aldimine 51, which cyclizes in situ to the aziridinophenanthrene 52 in low yield (9%). 

With Aromatic Aldehydes. To a solution of 10.3 g (20 mmol) of 2,3,4,6-tetra O-pivaloyl-/ -i>galactopyra-nosylaminc in 50 rnL of /-PrOI 1 or heptane are added 30 mmol of the corresponding aromatic aldehyde and 30 drops of acetic acid. After 30 min to 2 h, the Schiff base precipitates from the /-PrOH solution. When the reaction is carried out in heptane, 2 g of Na2S04 or 3 g of 3 A molecular sieves are added after 15 min, and the mixture is filtered. On cooling to 0 °C the Schiff base crystallizes from the heptane solution. The aldimines are collected by filtration and rapidly washed with ice-cold /-PrOH or pentane, respectively. Generally, they are pure enough for further transformations. 

The Schiff reaction between chitosan and aldehydes or ketones yields the corresponding aldimines and ketimines, which are converted to N-alkyl derivatives upon hydrogenation with borohydride. Chitosan acetate salt can be converted into chitin upon heating [130]. The following are important examples of modified chitosans that currently have niche markets or prominent places in advanced research. 

The fluoboric acid-catalyzed aza-Diels-Alder reaction of aldimine and Danishefsky s diene proceeds smoothly to afford dihydro-4-pyridones in high yields [90] (Equation 4.16). Unstable aldimines generated from aliphatic aldehydes can be prepared in situ and allowed to react under one-pot reaction conditions. This one-pot Bronsted acid-catalyzed three-component aza-Diels-Alder reaction affords the adducts in good to high yields. 

Reaction of metalated aldimines with aldehydes or epoxides... 

Reductive coupling of aldimines obtained from aromatic aldehydes and aromatic amines to generate vicinal diamines mediated by indium was carried out in aqueous ethanol (Eq. 11.59)." Small indium rods were used in this study. No side-product was observed due to unimolecular reduction. The presence of NH4CI was found to accelerate the reaction. The reaction fails completely in CH3CN, DMF, or wet DMF. The use of nonaromatic substrates also resulted in the failure of the reaction. 

The montmorillonite KlO-catalyzed aza-Diels-Alder reaction of Danishefsky s diene with aldimines, generated in situ from aliphatic aldehydes and p-anisidine, proceeded smoothly in H20 or in aqueous CH3CN to afford 2-substituted 2,3-dihydro-4-pyridones in excellent yields (Eq. 12.47).115 Also, complex [(PPh3)Ag(CBiiH6Br6)] was shown to be an effective and selective catalyst (0.1 mol% loading) for a hetero-Diels-Alder reaction with Danishefsky s diene and the reaction showed a striking dependence on the presence of trace amounts of... 

In general, an aldimine is among the least reactive carbonyl compounds and is by far less reactive than an aldehyde [31-33]. Nevertheless, the Et2Zn-Ni catalytic system is successfully extended to the homoallylation of aldimine. Aldimine prepared in situ from an aldehyde and a primary aromatic amine undergoes the homoallylation smoothly under the essentially identical con-... 

The reaction can be performed in one flask with great operational ease a mixture of an aldehyde and p-anisidine is stirred in THF for 5-10 h at 50 °C. Then, without removing the water produced, Ni(acac)2, isoprene, and Et2Zn are added in this order at room temperature. The mixture is stirred at the same temperature for the period of time indicated (Table 8). The products 57 and 58 are isolated as a mixture by column chromatograph after the usual work-up. Table 8 demonstrates the scope regarding the kind of aldehyde that encompasses not only aromatic aldehydes but also aliphatic aldehydes and even the parent formaldehyde. Despite the diminished electrophilic reactivity of aldimines, the reaction is complete at room temperature within a reasonable reaction time. The reaction of aldimines proceeds in an opposite sense of stereoselectivity to that of aldehydes and selectively provides 1,3-syn isomers 57. 

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