Photochemical syntheses. IV.The formation of 1-Alkoxynaphthalene-diphenylacetylene photo-adducts and their acid-catalysed hydrolysis. A new route to 2a, 8b-Dihydrocyclobuta[α]naphthalenes
1-Methoxy-, 1-ethoxy-, and 1-isopropoxy-naphthalene react with diphenyl- acetylene (dpa) to give the photo-adducts (2), (3), and (4) in 90-95% yield. The adducts (5), (6), and (7) each account for less than 1%. Each 1-alkoxynaphthalene gives also less than 5% of ketone (10) which is formed also by hydrolysis of two 4-alkoxy-1,2-diphenyl- 2a,8b-dihydrocyclobuta[a]naphthalenes. Several 2-substituted naphthalene-dpa photo-adducts rearrange in the presence of acid quantitatively into 4-substituted 1,2-diphenyl-2a,8b-dihydrocyclobuta[a]naphthalenes Likely intermediates in these rearrangements are discussed. 2-Methoxy-, 2-ethoxy-, and 2-isopropoxy- naphthalene do not add dpa. The first two compounds form photodimers but 2-isopropoxynaphthalene does not do so, and photo-dimerization is not the cause of the failure of 2-alkoxynaphthalenes to add dpa.