Aromatic dehalogenations

Deprotection of N-Cbz and N-Bn derivatives Deuterium-labeled Aromatic Dehalogenation... 

It is interesting to remark that classical hydrogenation is a method used to prepare deuterium-labeled compounds by aromatic dehalogenation, but the usual reaction conditions suffer from several limitations. A microwave-enhanced catalytic dehalogenation procedure for rapid and specific deuterium labeling of N-4-picolyl-4-halogenobenzamide 68, by use of deuterated formate, [41] was recently reported (Scheme 8.25). 

Aromatic dehalogenation suffers from the disadvantage that only 50% of the tritium is incorporated, the rest appearing as waste. This situation is even more marked for borotritide reductions but the problem can be overcome by using some of the new tritide reagents that have recently become available as a result of the synthesis of carrier-free lithium tritide (Scheme 13.1) [22], Their reactivity can be fine-tuned through the elements (e. g. B, Al, Sn) to which the tritium is attached and by the electronic and steric nature of the substituents at the central atom. 

Jones, J.R., Lockley, W.J.S., Lu, S.Y. and Thompson, S.P, Microwave-enhanced aromatic dehalogenation studies a rapid deuterium-labelling procedure,Tetrahedron Lett., 2001, 42, 331-332. 

The work of Jones and Lu has embraced a wide range of reactions including hydrogenations, borohydride reductions, aromatic dehalogenations, decarboxylations and hydrogen isotope exchange processes, (Scheme 9.3, Eqs. 1-3). In addition to the accelerated rates of reaction, new environmentally friendly routes have been developed, particularly solventless reactions that minimise waste production and facilitate containment107-110. 

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