J. Takagi et al. / Tetrahedron Letters 43 (2002) 5649–5651
5651
complexes are known to activate a C–H bond at the
2-position of 2.16 Therefore, C–H activation at the
2-position of 2 by tris(boryl)iridium(III) intermediates,
followed by C–B bond formation, is a reasonable mech-
anism for borylation of 2. However, the regioselectivity
of the borylation of pyridine and quinoline to give
3-borylated products is perplexing. One possibility is that
an iridium complex or a boron compound binds reversibly
to the basic nitrogen and both activates the substrate for
reaction and blocks borylation at the 2-position.
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[IrCl(COD)]2 (0.015 mmol), dtbpy (0.03 mmol), and
pin2B2 1 (1.0 mmol) was flushed with nitrogen, and then
charged with octane (6 ml) and thiophene (10 mmol). The
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cally pure sample: H NMR (400 MHz, CDCl3, TMS) l
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