La(OTf) 3 -Catalyzed [3+2] Cycloaddition Reactions for the Synthesis of Benzo[ d ]oxazoles/Benzofurans.

The La(OTf) 3 -catalyzed [3+2] cycloaddition reactions for the synthesis of benzo[ d ]oxazoles/benzofurans via quinones and 1,2-di- tert -butyl-3-(cyanimino)diaziridine (1,3-di- tert -butyl-2-cyanoguanidine)/vinyl azides have been explored. A series of 5-hydroxybenzofuran-4-carboxylic acid derivatives and 5-hydroxybenzo[ d ]oxazole-4-carboxylic acid derivatives were conveniently obtained with high yields and good stereoselectivities, which could be used for further transformations to valuable compounds.