Tritium tritiodehalogenations

There is a much wider variety of indirect replacement approaches. In most cases these approaches introduce the labels at structurally predefined positions generated by (formally) oxidative processes, which are then followed in a second step by reductive operations. Examples of such approaches preferentially designed for the introduction of tritium include halogenation followed by tritiodehalogenation, the introduction of carbon-carbon multiple bonds followed by catalytic tritiation, the oxidation of carbon-heteroatom bonds followed by reduction using tritide reagents, etc. These approaches, which do not alter the skeleton of the target in the process, are discussed in Chapter 4, Sections 1-3 and Chapter 10, Sections 10.1.1.2. ... 

In contrast to tritiations (reductions in which tritium is added to unsaturated substrates) tritiolyses are reductive reactions in which tritium replaces another atom or group. The most common class of tritiolyses is replacement of halogen (tritiodehalogenations), but some use... 

As with tritiations of carbon-carbon multiple bonds, catalytic tritiodehalogenations are favored by polar and protic solvents, such as methanol, ethanol, and water. On the other hand, catalyst-mediated /H exchange between solvent and tritium gas may give rise to a... 

Ci/mmol), [8- H]adenosine (20-30 Ci/mmol), [5- H]cytidine (10-30 Ci/mmol), 2 -deoxy [5- H]cytidine (10-30Ci/mmol), 2 -deoxy[5- H]uridine, (5-15 Ci/mol), [8- H]guanosine (10-30 Ci/mmol), [methyl- HJthymidine (25-30 Ci/mmol), and [5- H]uridme " . In some cases simultaneous incorporation of tritium into remote positions by H/H exchange processes has been reported. For example, incorporation exclusively into adenine-C2 has recently been accomplished during the tritiodehalogenation of a bromoadenosine-5 -triphosphate in phosphate buffer pH 8.6 in the presence of PdO as a catalyst . 

The preparation of monotritiomethyl iodide by catalytic tritiodehalogenation of bis-chloromethyl ether, chloromethyl 4-phenylbenzoate or chloromethyl phenyl sulfide with tritium gas over 10% Pd/C in ethyl acetate or DMF in the presence of a tertiary amine, and subsequent cleavage of the resulting [ H]methyl ether, ester or sulfide is addressed in Section 4.2.1 Yields are usually in the range of 30-60%. 

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