Schiff bases, lithiated

The morpholin-4-yl substituent in 7-position behaves similarly to the ethoxy group. Compound 481 is easily prepared by double addition of benzotriazole to acrolein followed by elimination of one of the benzotriazolyl moieties induced by treatment with NaH. Lithiation of derivative 481 followed by addition to a Schiff base results in formation of diarylpyrrole 476. Lithiated product 481 is alkylated exclusively at the carbon a, in relation to the benzotriazolyl substituent, giving intermediate 482. Subsequent treatment with a Grignard reagent leads to enamine 483 (Scheme 79) <1995TL343>. 

For further investigations f-BuNC, which is isolobal to CO, was used. With PhLi and t-BuLi, the characteristic vibrational mode of the lithium isonitrile adduct (2135 cm ) was observed at a lower wavenumber than that of the free isonitrile (2179 cm ). Unfortunately, n-BuLi did not undergo complexation. As indicated by the C=N stretching vibrational mode at 1510 cm, only f-BuLi—CN—R reacted further to afford the lithiated Schiff base up to —20°C (equation 2) . ... 

Only the most reactive organolithium compound, e.g. f-BuLi, is able to attack the carbon-nitrogen triple bond at temperatures below —20°C. For the other less reactive species, namely PhLi and n-BuLi, higher temperatures in ordinary solvents like pentane would be more appropriate to synthesize their lithiated Schiff bases. Flowever, for their detection IR spectroscopy seems to be unsuitable, since the relevant C=N stretching mode will be hidden by strong CH deformation modes of the solvent. 

The stereochemical course in addition of lithiated benzyl cyanide and propioni-trile to aromatic Schiff bases has been investigated and the origin of the stereochemical results has been discussed.44 A carbanionic intermediate with an adjacent (g stereogenic centre, formed as a result of fast isomerization of the initially formed azanions, has been proved to be involved in the formation of the stereochemical ratios. 

Katritzky and coworkers have developed two new methods of pyrrole synthesis involving condensation of C3-C4-C5 synthons with Schiff bases to obtain 1,2-diaryl pyrroles. The synthon 2a is obtained by condensation of acrolein, morpholine and benzotriazole, followed by a base-catalyzed elimination. Lithiation gives an anion which adds to the imine. Cyclization occurs on acid treatment. <95TL343> An alternative synthon is obtained by lithiation of 2b. <95S1315>... 

Phosphorylglycines are easily prepared, but in limited yield, by alkoxycarbonylation of the a-lithiated Schiff base of diethyl aminomethylphosphonate in THF at low temperature. The acylated Schiff base is converted in high yield (80%) to the corresponding p-lactam by photochemical reaction with the [(methoxy)(methyl)carbene]chromium complexes in CHjCF. ... 

Stork overcame the dialkylation problem at the a-carbons in aldehydes by using imines. The obvious disadvantages of this method are the unstable starting materials (Schiff bases). Meyers and coworkers found that the stable commercial starting material 2,4,4,6-tetramethyl-5,6-dihydro-l,3-4A/-oxazine 43 can be used as a precursor for formation of various aldehydes. After lithiation of the methyl group in the 2 position it acts as an excellent nucleophile in reaction with various electrophiles E, and after reducing the double bond and hydrolysis the aldehyde group is formed (equation 15). 

A versatile starting material for the preparation of compounds belonging to the second class of polymers is (19) (R = Br) via a lithiation step numerous compounds have been prepared (19) (R = PPh2) readily forms complexes with transition metal compounds. Reduction of (19) (R = NO2) gives (19) (R = NH2), that can be used in diazotization and subsequent diazo coupling reactions. Another application of (19) (R = NH2) involves Schiff base... 

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