The design of medium access control (MAC) in wireless sensor networks (WSNs) poses several key factors such as energy conservation, bandwidth utilization, throughput, etc. This paper proposes a new MAC protocol referred to as DEE-MAC which reduces energy consumption by making the idle nodes sleep to reduce idle listening using synchronization at cluster heads. Each cluster is dynamically formed as all nodes contend for the position of cluster-head and join and leave process is freely done. Simulation result shows that the proposed MAC protocol outperforms other existing MAC protocol.