Pyridylmethyl groups

The diphenyl-4-pyridylmethyl group is cleaved by Zn/AcOH, 1.5 h, 91% yield H2/Pd-C, 91% yield or by electrolytic reduction, 2.5 h, 0°, 87% yield. The Dppm group is stable to trifluoroacetic acid. " ... 

The combination of pyridine and aliphatic nitrogen donors creates an intermediate ligand field which has yielded a long list of spin crossover systems [2]. Recently, Kahn et al. obtained two new tetradentate ligands in which two 2-pyridylmethyl groups replace two hydrogen atoms on the same amine function in 1,2-diaminoethane and 1,3-diaminopropane (4, 5) [5-6]. 

A potentially octadentate N8 ligand, derived from b -bisCaminomethyl)-2,2/-bipyridine by attaching four 2-pyridylmethyl groups, has been prepared by Toftlund et al. (29). 

A number of other groups can be used for the protection of thiols benzyl thioethers of amino acids and peptides have been cleaved electrochemically at a platinum cathode in liquid ammonia [121], at mercury in MeOH-TMACl [122], and in DMF [123,124], and the trityl group has been used to protect cysteine cysteine was recovered in 90% yield after reduction in DMF [124]. The 4-pyridylmethyl [125,126] and diphenyl-4-pyridylmethyl groups can be cleaved in acid solution [124] at a mercury cathode. 

Maruszewska-Wieezorkowska, E., and Michalski. J., Alkyl and alkenyl pyridines. Part 9. Phosphonates and tertiary phosphine oxide containing 2- and 4-pyridylmethyl groups at the phosphorus atom, and some of their reactions, Rocz. Chem.. 38. 625. 1964. 

Scheme 11.8 A tentative mechanism for 2-pyridylmethyl group transfer.

The carboxyl group is esterified in the process and has to be deblocked by saponification with alkali to allow its activation for subsequent incorporation. Deprotection of the imidazole can be achieved by catalytic hydrogenation although sometimes difficulties are encountered in this step. An alternative method of debenzylation, treatment with acetic acid, must be carried out at fairly high temperature. More acid sensitivity is shown by the im-trityl derivative while the diphenyl-4-pyridylmethyl group is acid resistant ... 

The properties of calixarene-based host molecules are strongly influenced by the conformation of the calixarene moiety. Pyridinocalix[4]arenes are conforma-tionally inflexible molecules (the introduction of just one pyridylmethyl group at the lower rim suffices to suppress conformational changes), while the larger calix[6]arene homologues show fluxional properties. 

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