Potential green fungicide: 16-oxo-1-oxa-4-azoniacyclohexadecan-4-ium tetrafluoroborate

16-Oxo-1-oxa-4-azoniacyclohexadecan-4-ium tetrafluoroborate (2a) and its sulfonyl derivatives (2b-2i) were synthesized, their structures were confirmed by 1H NMR and elemental analysis and their fungicidal activities were investigated. Among them, compound 2a was not only more effective than compounds 2b-2i against the Rhizoctonia solani Kuhn in vitro bioassay, but also better than the commercial fungicide Carbendazim both in pot culture experiments and field efficacy trial. These results once again proved the correctness of our original proposal that macrocyclic compounds with two polarizable groups (one hydrogen-bonding donor and one hydrogen-bonding acceptor) on the ring may have certain good bioactivity. Furthermore, 2a has low toxicity, is safe for human beings, and its synthesis is a green and most economical process, because the atoms of the starting materials are almost fully utilized.