  The order of the thermal phase transition in the chiral limit of Quantum
Chromodynamics (QCD) with two dynamical flavors of quarks is a long-standing
issue and still not known in the continuum limit. Whether the transition is
first or second order has important implications for the QCD phase diagram and
the existence of a critical endpoint at finite densities. We follow a recently
proposed approach to explicitly determine the region of first order chiral
transitions at imaginary chemical potential, where it is large enough to be
simulated, and extrapolate it to zero chemical potential with known critical
exponents. Using unimproved Wilson fermions on coarse $N_t=4$ lattices, the
first order region turns out to be so large that no extrapolation is necessary.
The critical pion mass $m_\pi^c\approx 560$ MeV is by nearly a factor 10 larger
than the corresponding one using staggered fermions. Our results are in line
with investigations of three-flavour QCD using improved Wilson fermions and
indicate that the systematic error on the two-flavour chiral transition is
still of order 100\%.
