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ABSTRACX Deuterium exchange labelling experiments were conducted on several series of compounds, including para-substituted benzoate esters, para-substituted N,N-dimethylbenzamides, and mono-para-substituted benzophenones, using [IrH2(MezC0)2(PPh3)2]BF4 as catalyst and deuterium gas as the source of isotope. In most cases, labelling was efficient and regioselective, with deuterium appearing in the positions ortho to the carbonyl-containing functional group. Apparent from the results of these experiments was that, in each case the para-substituted rings were labelled more rapidly or to a greater extent than the corresponding unsubstituted rings, regardless of the identity of the substituent. We have recently described132 preliminary results of studies of deuterium exchange labelling of substrates with deuterium gas, catalyzed by [IrHz(MezC0)2(PPh3)21BFq, which displayed significant efficiency and regioselectivity in a range of substrate structural classes. We have continued to explore this area of exchange catalysis, with several aims: to learn something about the nature of the exchange process catalyzed by this complex, to expand the scope of the method, and to investigate the activity of related complexes. In this communication we report the results of exchange studies conducted on several series of substituted aromatics, with the objective to investigate the stereoelectronic effects of substituents on the exchange process. A number of p-substituted benzoate esters were treated as shown in Scheme 1. The products were isolated by evaporation of the solvent and extraction of the residue with ether, then analyzed by 1H NMR and MS in order to ascertain the amount and location of incorporated deuterium. In no case was a significant amount of any side reaction (e.g., reduction) detected, and recoveries were usually >%%. The deuterium labelling results are summarized in Table 1. |
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