Cycloadditions in syntheses. XXVI 1,2-Dihydrocyclobuta(b)naphthalene-3,8-diones : Synthesis by photochemical means and their reactions via 2,3-dimethylene-1,4-dioxo-1,2,3,4-tetrahydronaphthalenes.

Abstract

2-Chloro-1, 4-naphthoquinone undergoes photochemical 2+2 addition to alkenes. Elimination of hydrogen chloride from the adducts provides a facile and general synthetic method for 1, 2-dihydrocyclobuta[b]naphthalene-3, 8-diones. Heating of the latter compounds affords 2, 3-dimethylene-1, 2, 3, 4-tetrahydronaphthalene-1, 4-diones, which react in situ with alkenes to give the 4+2 adducts. 1-Formyl-1, 2-dihydrocyclobuta[b]naphthalene-3, 8-dione obtained by the use of the above two-step procedure using acrolein dimethylacetal as the alkene in the first step affords upon heating 1H-naphtho[2, 3-c]pyran-2, 10-dione via electrocyclization of the corresponding dimethylenecompound. If an enone is used as the alkene in the first step, the addition occurs in a 4+2 manner to give directly 4H-naphtho[2, 3-b]pyra-5, 10-diones.