Abstract:
A transition-metal-free hydrothiolation of 1,3-
dienes for the synthesis of secondary and tertiary allylic sulfides
is reported. The boron Lewis acids tris(pentafluorophenyl)-
borane, B(C6F5)3, and BF3·Et2O are shown to catalyze the
regioselective hydrothiolation of a wide range of terminal 1-aryl1,3-dienes. In the case of internal 1,3-dienes, B(C6F5)3 is by far
the better catalyst than BF3·Et2O. The process features mild
reaction conditions, broad scope, and low catalyst loading, and it
can be scaled up quickly over a short reaction time. The
reactions are rate-limited by the 1-aryl-directed protonation of
1,3-dienes with thiol-boron Lewis acid complexes, followed by
sulfide anion transfer to the resultant allyl cations, as revealed by
high-level DFT calculations.
