  Recent work on QCD-like theories has shown that the addition of adjoint
fermions obeying periodic boundary conditions to gauge theories on $R^{3}\times
S^{1}$ can lead to a restoration of center symmetry and confinement for
sufficiently small circumference $L$ of $S^{1}$. At small $L$, perturbation
theory may be used reliably to compute the effective potential for the Polyakov
loop $P$ in the compact direction. Periodic adjoint fermions act in opposition
to the gauge fields, which by themselves would lead to a deconfined phase at
small $L$. In order for the fermionic effects to dominate gauge field effects
in the effective potential, the fermion mass must be sufficiently small. This
indicates that chiral symmetry breaking effects are potentially important. We
develop a Polyakov-Nambu-Jona Lasinio (PNJL) model which combines the known
perturbative behavior of adjoint QCD models at small $L$ with chiral symmetry
breaking effects to produce an effective potential for the Polyakov loop $P$
and the chiral order parameter $\bar{\psi}\psi$. A rich phase structure emerges
from the effective potential. Our results are consistent with the recent
lattice simulations of Cossu and D'Elia, which found no evidence for a direct
connection between the small-$L$ and large-$L$ confining regions. Nevertheless,
the two confined regions are connected indirectly if an extended field theory
model with an irrelevant four-fermion interaction is considered. Thus the
small-$L$ and large-$L$ regions are part of a single confined phase.
