This paper aims at introducing an extension of M-nets, a fully compositional class of high-level Petri nets, and of its low-level counter part, Petri Boxes Calculus (PBC). We introduce a new operator with nice algebraic properties which allows to express asynchronous communications in a simple and flexible way. With this extension, asynchronous communications become at least as simple to express as (existing) synchronous ones. Finally, we show how this extension can be used in order to specify systems with timing constraints.