Hydrogenolysis, aromatic molecular

Reductive animation of aromatic aldehydes to give benzylamines is accomplished by heating the aldehyde and tritylamine with molecular sieves, followed by the addition of sodium cyanoborohydride. Catalytic hydrogenolysis of the products with palladium on charcoal yields the benzylamines (equation 56)167. 

The first compound, in approximately 4% yield, was regarded as demethoxydihydroschelhammeridine (44) which is presumably formed by hydrogenolysis of the allylic methoxy group at C-3 of 38 followed by 1,4 addition of hydrogen to the dienone system. The second product was obtained in 30% yield and has been shown to be l,2,6ce,7-tetra-hydroschelhammerine (45). The stereochemistry shown at C-6 of 45 cannot be deduced from spectral data but inspection of molecular models indicates that the attack from the side of the molecule is hindered by the bulky aromatic ring. The third compound, obtained in 30% yield, was postulated to be dihydroschelhammeridine (35), which was identical with schelhammericine, a natural product. The formation of 35 can be readily explained by 1,4 addition to the diene system. Further attempts to reduce it under the same conditions have been unsuccessful. The fourth minor product has been shown to be the... 

Compound 193 (Fig. 82) with molecular formula C20H28O4 6-(3-methyl-2-butenyl)-5-hydroxy-2,2-dimethyl-8-(2-methylpropanoyl)-1,4-benzo(3H)pyran. It has also been isolated by preparative thin layer chromatography. The red shift by 40 nm of the UV absorption maximum in alkaline conditions is typical for a para-acylphenol derivative (11). The H NMR spectrum shows the presence of the 2-methylpropanoyl side chain next to a dihydropyran ring and a 3-methyl 2-butenyl group. Hydrogenolysis of compound 194 (Fig. 82) (see 13.2.1.3.) leads to compound 196 (Fig. 82), which is identical to that obtained upon hydrogenation of 193. The formation of the aromatic derivatives 189, 190, 192 and 193 requires the loss of an isopentenyl side chain. Aromatization of colupulone occurs in strong acid (see 4.1.) or by catalytic... 

The fragment found at m/z 59 in the mass spectrum proves the presence of a dimethyicarbinol group. This is possible only when the cyclization leads to a dihydrofuran derivative. Distinction between the positional isomers 223 and 224 (Fig. 93) is based on the results of the hydrogenolysis with palladium on carbon as catalyst. The crystalline aromatic compound 225 (Fig. 93) with a melting point of 150.5-151.5°C shows a molecular ion at m/z 350 and UV absorption maxima at 292 nm in acidic ethanol and at 330 nm in alkaline ethanol, in the H NMR spectrum the... 

Many physical properties of hyperbranched aromatic polyesters, such as high solubility and low viscosity, resemble those of dendrimers. However, in contrast to dendrimers, hyperbranched polymers do exhibit a linear dependence of intrinsic viscosity on molecular weight with very low Mark-Houwink constants (0.3-0.4) [13]. In addition, their lack of reactivity toward catalytic hydrogenolysis greatly differs fi om that of the corresponding dendrimers, which are cleanly deprotected under mild conditions rather their reactivity more resembles that of the corresponding linear polymers [59]. As shown in... 

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