Benzylidene-aniline, preparation

Hydroxy-8,9-methylenedioxyphenanthridine, [10]. The method developed by Kessar et al. [11] for phenanthridines and related compounds was applied to the synthesis [10] of 3-hydroxy-8,9-methylenedioxyphenanthridine (22) (Scheme 5). Thus, the benzylidene aniline 23, prepared from 6-chloropiperonal and 3-benzyloxyaniline, was reduced to the secondary amine 24. Treatment of 24 with excess lithium diisopropylamide furnished, on work-up, the benzyl ethers 25 (22%) and 26 (6%) respectively. Catalytic debenzylation of the former generated 22. 

With the bidentate o-(diphenylphosphino)benzaldehyde (PO) and o-[(diphenylphosphino)benzylidene]aniline (PN) ligands the complexes [ReX(CO)3(PO)] (X is halide, 94) and [ReX(CO)3(PN)] (X is halide, 95) have been synthesized and characterized, starting from [ReX(CO)5] (X is Br, Cl) [92]. Using the same starting material, complexes of the type/ac-[Re(CO)3(K 3-L) (96) were also prepared, where L is a phosphorus-containing heterotridentate ligand, obtained by condensation of 2-(diphenylphosphino)aniline with several salicylaldehyde derivatives (Scheme 24) [93]. 

Amino acids may also be prepared from azomethine compounds by reducing them in the presence of carbon dioxide [34—38]. Thus reduction of benzylidene aniline (IV) in molten tetraethylammonium -toluenesulfonate saturated with carbon dioxide at 140°C gave V-phenyl-phenylglycine (60% yield) [34], [Eq. (9)]. In DMF a similar yield was obtained together with small amounts of a dimer and some phenylbenzylamine [38]. 

In the 1980s, Gallardo and Muller [51] andBennuret al. [52] described the reaction of 4,4 -dialkyloxybenzoines with 4-substi-tuted anilines, which they claimed yielded liquid crystalline benzoinylidene anilines 17. However, there were indications, e.g. from the experimental details given, that the dialkyloxybenzoines were not isolated in the pure state. Therefore, by reaction of the raw intermediates with anilines simple 4,4 -disubstituted benzylidene anilines 18 were prepared (Table 6). 

More recently, so-called photoresponsive crown ethers have also been prepared and, in these too, the light-sensitive behavior is based on Z,E-isomerization. The study of azo-groups in polymers has been undertaken recently. Switching processes have been an intensively studied domain in recent years as show in some recent papers. > Z,E-isomerization also plays an important role in simpler compounds such as benzylidene anilines and azomethines. The latter are of importance in biological systems such as rhodopsin in the human eye. ... 

When 2-amino-5-chloro-3-methoxycarbonylpyrazine was refluxed with aniline and concentrated hydrochloric acid in acetone for 16 hours, the anil, 5-anilino-2-isopropylideneamino-3-methoxycarbonylpyrazine (22) was formed (432, 778, 780), and 2-amino-5-chloro-3-methoxycarbonyl-6-(l -methylhydrazino)pyrazine with benzaldehyde in ethanol gave 2-amino-6-(2 -benzylidene-r-methylhydrazino)-5-chloro-3-methylcarbonylpyrazine (23) (809). A series of hydrazones has been prepared by refluxing equimolar quantities of 2-hydrazinopyrazine and carbonyl compounds in the presence of catalytic quantities of p-toluenesulfonic acid in benzene (1195). Other preparations of similar hydrazones have been described (1196). 

In the previous section, lanthanide triflates were shown to be excellent catalysts for achiral aza Diels-Alder reactions. While stoichiometric amounts of Lewis acids are required in many cases, a small amount of the triflate effectively catalyzes the reactions. On the other hand, chiral lanthanide Lewis acids have been developed to realize highly enantioselective Diels-Alder reactions of 2-ox-azolidin-l-one with dienes [89]. The reaction of N-benzylideneaniline with cyclop entadiene was first performed under the influence of 20 mol% of a chiral ytterbium Lewis acid prepared from ytterbium triflate (Yb(OTf)3), fR)-(+)-l,l -bi-naphthol (BINOL), and trimethylpiperidine (TMP). The reaction proceeded smoothly at room temperature to afford the desired tetrahydroquinoline derivative in a 53% yield, although no chiral induction was observed. At this stage, it was indicated that bidentate coordination between a substrate and a chiral Lewis acid would be necessary for reasonable chiral induction. N-Benzylidene-2-hydroxy aniline (31a) was then prepared, and the reaction with cyclopentadiene (32a) was examined. It was found that the reaction proceeded smoothly to afford the corresponding 8-hydroxyquinoline derivative (33a) [90] in a high yield. The enantiomeric excess of the cis adduct in the first trial was only 6% however, the selectivity increased when diazabicyclo-[5,4,0]-undec-7-ene (DBU) was used in-... 

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