Most existing tools for the synthesisof asynchronouscircuits from Signal Transition Graphs (STGs) derive the reachability graph for the calculation of logic equations. This paper presents novel methods exclusively based on the structural analysis of the underlying Petri net. This methodology can be applied to any STG that can be covered by State Machines and, in particular, to all live and safe free-choice STGs. Significant improvements with regard to existing structural methods are provided. The new techniques have been implemented in an experimentaltool that has been able to synthesizespecificationswith over1027 markings,some of them being non-free choice.