Benzyl cleavage

WILKINSON Cartxinylalion decarbonylation catalyst Rh catalyst lor cartxinylation, decarbonylation, oxygenation, benzyl cleavage... 

Note that in this example the ester was not reduced. When R = Ac, the benzyl cleavage reaction failed. ... 

Mass spectra of OPEOs, their acidic metabolites, OPEC and halogenated derivatives in El and Cl modes have been reported [80-82]. The most prominent ions formed under Cl resulted from alkyl ion displacement and olefin displacement, and those formed under El resulted from benzylic cleavage [82]. 

Example The ratio [M-CH3]V[M-CD3] from isopropylbenzene molecular ions decomposing by benzylic cleavage (Chap. 6.4) varied from 1.02 for ion source fragmentations (70eVEI) over 1.28 for metastable ions in the FFR to 1.56 in the 2 FFR, thus clearly demonstrating the dependence of the secondary kinetic isotope effect on internal energy. [77]... 

Example In the mass spectrum of /er/-butylbenzene, C10H14, M = 134, the [CvHv]" ion is formed by C2H4 loss from the product of benzylic cleavage, m/z 119, despite such a rearrangement would not be expected at first sight (Fig. 6.15). 

Fig. 6.28. El mass spectrum of (3-methylpentyl)-benzene. McLafferty rearrangement and benzylic cleavage are clearly dominating. In the low-mass range carbenium ions and the aromatic fragments are present. Spectmm used by permission of NIST. NIST 2002.

As previously described, thermolysis of aziridines is one of the standard methods for the generation of azomethine ylides. A diastereomeric mixture of the aziridines 199 possessing an enantiomerically pure N-substituent underwent ylide formation at 280 °C and subsequent cycloaddition to vinylidine carbonate to form a mixture of four separable compounds (d-200, l-201, d-202, l-203) in a 3 3 1 1 ratio (55). Subsequent LiAlH4 reduction and hydrogenolytic N-benzyl cleavage led to all... 

The mass spectral features of hydroporphyrins are dominated by the benzylic cleavage of / substituents on the saturated carbons.2,14... 

Table 17), but cyclization of -substituted carbamates is highly selective (entries 2,4 and 5), presumably by insuring reversible formation of the intermediate prior to benzyl cleavage and steric interactions between the -substituent and the alkyl substituent favoring the axial orientation (equation 61). Cycliza-tions of this type, where R = H and Y = a-phenethyl, result in little asymmetric induction. However, the diastereomeric products can be separated and used for the synthesis of chiral nonracemic amino alcohol derivatives.164... 

Thalictrum sultanabadense Stapf was the source of the amorphous base thalbadenzine (295), MS m/e 594 (M+) and 381 (doubly benzylic cleavage). 

The presence of an imine function in coclobine and 12-0-demethylcoclobine was deduced from the very low mass spectral relative abundance of the bisiso-quinoline fragment that normally results from double benzylic cleavage of bis-benzylisoquinolines (55), as well as from the acid-induced bathochromic shift in... 

WILKINSON Carbonylalion decarbonylatnn catalyst Rh catalyst tor carbonylatnn, decartonylation, oxygenatwn. benzyl cleavage... 

Oxazoles with 5-alkyl substituents can undergo benzylic cleavage (Equation 1) and for 2-alkyl-substituted oxazoles, McLafferty rearrangement often takes place (Equation 2). 

In one additional example, illustrating the applicability of the Ferrier cyclization to amine-based substrates, the same strategy allowed the synthesis of carba-glucosamine (Scheme 8.33). Starting from Cbz protected methyl a-D-glucosaminide 123, 4,6-benzylidene formation, di-benzylation, cleavage of the acetal, regioselective iodination and simultaneous elimination... 

---