Benzylic carbonylation

The mechanism is postulated to involve the initial formation of a Schiff base 17 from the condensation of the anilinic amine 16 with the carbonyl-containing substrate. This is followed by a Claisen condensation between the benzylic carbonyl and the activated a-methylene of the imine. ... 

The main mass fragmentation of secobenzylisoquinoline alkaloids involves bond cleavage between the two benzylic carbonyls. This process is evidenced by the presence of peaks representing fragment ions at m/z 151, found in spectra of all these bases and attributed to the lower portion of the molecules, and ions at m/z 220,236, and 222, found in spectra of 159,160, and 161, respectively, formed from the upper part of the compounds. Similarly, as in the mass spectra of other secoisoquinoline alkaloids incorporating the amino-ethyl substituent, the [H2C=N(CH3)2]+ ion at mjz 58 is the base peak. 

A study of the hydration of HC=CPh in the presence of mer, trows-RuCl2(PPh3) NPr(CH2CH2PPh2)2 showed the intermediacy of vinylidene, aquo(alkynyl), acyl and benzyl(carbonyl) complexes [282]. 

C. Acid-Catalyzed Acylation of Benzyl Carbonyl Compounds and Their... 

The formation of 2-benzopyrylium cations 30 by acid-catalyzed acylation of benzyl carbonyl compounds 28 may be described by several equilibrium processes as shown in Scheme 2. 

The direct interaction of benzyl carbonyl compounds 38 and 48 with aromatic aldehydes in the presence of PPA or AC2O + HC104(86KGS125 87TH1), or with acetals or acylals of aliphatic or aromatic aldehydes in the presence of triphenylmethyl perchlorate (73KGS881 75ZOR1962), gives rise to benzo[c]pyrylium salts 62 in yields of 15-70 %. 

Upon acylation of some benzyl carbonyl compounds (25, R = H, Me 51, R = OH) dibenzo[a,tropylium salts 65 have been isolated in low yields (5-15 %) along with the major products, 2-benzopyrylium salts. Veratryl acetone 25 (R = Me) as well as homoveratric aldehyde 25 (R = H) (or carboxonium ions 31 which are formed from them) may undergo an oxidative a-cleavage, resulting in the benzyl cation 64. The formation of the same cation from homoveratric acid 51 is the result of decarbonylation of the acylium ion 63. Further interaction of the benzyl cation 64 with the substrate, followed by cyclization and oxidation, results in the polycyclic tropylium salts 65 (82ZOR589). 

Beginning with 6-methyl-2-oxo-4-phenoxy-3-[(benzyl-carbonyl)amino]-l,2-dihydropyridine-1-acetic acid, (I), a method for preparing (R)-N-borono[3-(lH-imidazol-4-yl)propyl]methyl]-3-[(benzyl-carbonyl)amino]-6-methyl-2-oxo-4-phenoxy-1,2-dihydropyridine-l-acetamide HCl, (II), as illustrated in Eq. I, is described by the author in the current invention. 

Replacement of the benzylic carbonyl oxygen of ketanserin by hydrogen or phenyl reduces affinity 5 fold [11,12], For the phenylethyl- and phenylbutyl analogues is the decrease in affinity 2 and 12 times respectively [12],... 

Reduction of the benzylic carbonyl group of desfluoro-ketanserin decreases the affinity for S-HTjy receptors 100 times [11] (Table 4). The N-ethyl substituted analogue even lost all affinity. However contrary to the expectations high affinity is maintained in the phenylethyl derivatives [12] (Table 4). 

A number of different chemical names have been applied to this reagent all are correct but the use of so many is confusing. Some of these names are carbobensozy chloride (209, 215), benzyl chloroformate (214), benzyl carbonyl chloride (213), the acid chloride of benzyl carbonic acid (212), and carbobenzyloxy chloride (216). Regardless of the merits of any particular name, the reviewer has chosen the one used most recently by workers in Beigmann s laboratory (215). 

In the same way that an aromatic ring activates a neighboring (benzylic) C H toward oxidation, it also activates a benzylic carbonyl group toward reduction. Thus, an aryl alkyl ketone prepared by Friedel-Crafts acylation of an aromatic ring can be converted into an alkylbenzene by catalytic hydrogenation over a palladium catalyst. Propiophenone, for instance, is reduced to propylbenzene by catalytic hydrogenation. Since the net effect of Friedel-Crafts acylation followed by reduction is the preparation of a primary alkylbenzene, this two-step sequence of reactions makes it possible to circumvent the carbocation... 

In a method which may only be applicable to the preparation of benzylic carbonyl compounds, Grignard reagents (stereospecifically) transform methyl-sulphinyl derivatives (7) into the anion [equation (6)]. Other than protonation, no further transformations of the arylacetaldehyde derivatives were described. 

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