Oxidation of Aromatic Lithium Thiolates
SCHEME 1. Sulfones via Lithium Sulfinates (*C ) 12C,
11C)
sodium benzenesulfinate (70% radiochemical yield after the
reaction in DMF at room temperature for 3 days).10 This strategy
obviously reduces the number of radioactive steps. However,
the limited availability and low nucleophilicity of the sulfinates11
made this reaction uncommon toward more sophisticated targets
and restrained any development in 11C chemistry.
In the course of our work concerning the reactivity of thiolates
with N-sulfonyloxaziridines,12 we have previously reported an
original synthesis of lithium arenesulfinates and identified the
benzaldehyde derivative 5 as the appropriate oxidizing agent
(Scheme 1).12b The main features of this new reaction are a
high efficiency, a remarkable chemoselectivity, a compatibility
with a wide range of substrates, and the use of mild conditions.
FIGURE 1. 11C-Sulfones as PET tracers (*, labeled position).
In addition, strong oxidizing reagents (H2O2, m-CPBA, or
oxone), required for a rapid reaction and used in large excess
as compared to the 11C-methyl sulfide, are not selective of the
sulfone function and might not be appropriate in the case of
polyfunctional molecules with sensitive groups.9
The main alternative route to sulfones involves the S
alkylation of sulfinate salts.9 This reaction has been used, for
example, for the labeling with 14C (â- emitter, t1/2 ) 5730 years)
of methylsulfonylbenzene, starting from commercially available
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This paper describes also the labeling of the COX-2 inhibitors Etoricoxib
and Rofecoxib.
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