Afterward, we extended the scope of the 1,2-functionalization
with respect to the aryne (Table 2). Gratefully, electron-rich,
inductively electron-withdrawing arynes and those with
expanded π-systems could be converted to the corresponding
1,2-difunctionalized products in 42−78% yield (Table 2, entries
1−3). Unfortunately, when using 2e bearing two fluorine
substituents, the desired thiobenzonitrile 3ae was only observed
by GC-MS in less than 5% yield (Table 2, entry 4), although 2e
was entirely consumed concomitant with mostly untouched
phenyl thiocyanate. In addition, when unsymmetrical aryne
precursors were employed, regioisomeric mixtures were
obtained in 45% up to 79% yield (Table 2, entries 5−7).
Noteworthy, in the cases of 2g and 2h the major isomers
contain the small nitrile residue next to the sterically
encumbered position as unequivocally shown by 2D-NMR
spectroscopic investigations.
To elucidate the mechanistic scenario we tried to capture
reaction intermediates. Therefore, phenylacetylene or styrene,
respectively, were added to trap the reactive species after the
first bond forming step has occurred through either carbo- or
thiopalladation. Unfortunately, exclusively thiobenzonitrile 3aa