Synthesis of benzocyclo-octene-5,6-dione, benzocyclo-octene-5,10-dione, and 2,3-benzobishomotropone derivatives by dichlorocarbene ring enlargement, and of 7,8,9,10, tetrahydrobenzocyclo-octene-5,6-dione
Abstract
Addition of dichlorocarbene by the use of a phase transfer catalyst to 1,4,5,8-tetramethoxynaphthalene (5) and to 2,3,4,6-tetramethoxybenzocyclohepten-5-one (9) afforded benzocyclo-octene-5,10-dione (2) and benzocyclo-octene-5,6-dione (4) together with 1,2:3,4-dimethylenenaphthalene (6) and 2,3-benzobishomotropone (10), respectively. Compounds (2) and (4) had no 8C-6π character. 7,8,9,10-Tetrahydrobenzocyclo-octene-5,6-dione (14) was synthesized by three different methods from 7,8,9,10-tetrahydrobenzocyclo-octen-5(6H)-one (12). This compound had an unusually rigid conformation and could not be converted into the benzocyclo-octene-5,6-dione (3).