  We present the calculation of the next-to-leading corrections to the tree
amplitudes which appear in the description of non-leptonic B-decays in the
factorization approach. These corrections, together with radiative corrections
to the jet functions, represent the full next-to-leading contributions to the
dominant hard spectator scattering term generated by operators $O_{1,2}$ in the
decay amplitudes. Using obtained analytical results we estimate $B\to\pi\pi$
branchings fractions in the physical (or BBNS) factorization scheme. We have
also found that the imaginary part generated in the hard spectator scattering
term is rather large compared to the imaginary part of the vertex contribution.
