Silicon disulphide and boron sulphide in the preparation of thiones and pyranthiones

Silicon disulphide and boron sulphide can be used with advantage instead of phosphorus pentasulphide for converting non-enolisable ketones, 2-pyrones and 4-pyrones into the corresponding thiones. Of the three reagents, boron sulphide is the most active and is often effective at ordinary temperatures. A convenient synthesis of 3,4-benzocoumarin is noted.