  We study the phase diagram of the 2D $J_1$-$J_1'$-$J_2$ spin-1/2 Heisenberg
model by means of the coupled cluster method. The effect of the coupling $J_1'$
on the Neel and stripe states is investigated. We find that the quantum
critical points for the Neel and stripe phases increase as the coupling
strength $J_1'$ is increased, and an intermediate phase emerges above the
region at $J_1' \approx 0.6$ when $J_1=1$. We find indications for a quantum
triple point at $J_1' \approx 0.60 \pm 0.03$, $J_2 \approx 0.33 \pm 0.02$ for
$J_1=1$.

Strongly Correlated Electrons