Typically, asynchronous Media Access Control (MAC) protocols are used to monitor a significant facility for rare events or to detect an intrusion in Wireless Sensor Networks (WSN). Moreover, asynchronous MAC protocols can achieve high energy efficiency due to the fact that there is no periodic control frame. However, asynchronous MAC protocols have the problem of long end-to-end delay time caused by the absence of precedent time synchronization per link. A new MAC protocol, WTE-MAC, is proposed by devising a new scheme, called Virtual Tunnel (VT), which can reduce the delivery delay of asynchronous MAC protocols in multi-hop environment. The Virtual Tunnel scheme can achieve approximated duty cycle synchronization with on-demand approach. In this scheme, through the estimation of next wakeup time of peer node, without exceptional process, each node on the transmission path can improve end-to-end delay in multi-hop topologies. And it becomes low power consumption by reducing unnecessary retransmissions. In our simulation results, end-to-end delay according to hop counts and traffic amount is compared with the X-MAC that is an asynchronous protocol recently developed. Furthermore, it is shown that the Virtual Tunnel scheme decreases energy consumption due to the lower end-to-end delay than the X-MAC in multi-hop topologies.