ELECTROCHEMICAL CLEAVAGE OF DOUBLE-BONDS IN CONJUGATED CYCLOALKENYL-ALKENOBENZENE AND 1,2-ALKENOBENZENE

The electrochemical cleavage of olefinic bonds in conjugated C-5-C-7-c ycloalkenylbenzenes 1, indene 4a, and 1,2-dihydronaphthalene (4b) resu lts from anodic oxidation of these compounds in MeOH in an undivided c ell. The process includes the formation of (1,2-dimethoxycycloalkyl)be nzenes 2a-c, 1,2-dimethoxyindan (5a), and 1,2-dimethoxytetralin (5b) a s intermediates and leads to ega,omega-dimethoxy-omega-phenyl-n-C-5-C- 7-alkanal dimethyl acetals 3a-c, [2-(dimethoxymethyl)phenyl]ethanal di methyl acetal (6a), and 3-[2-(dimethoxymethyl)phenyl]propanal dimethyl acetal (6b) as major products, respectively. The best yields of 3a-c and 6a,b (58-76%) were obtained when the electrolysis was carried out at 60 degrees C and 6 F/mol of electricity based on 1, 4a, and 4b, was passed using C-anode and Bu(4)NBF(4) as a supporting electrolyte. Com pounds 2a-c and 5a,b as mixtures of cis and trans diastereomers were o btained as major products in 81-90% yield when the electrolysis was te rminated after 2 F/mol of electricity based on 1, 4a, and 4b had been passed. The cis/trans ratio in 2a-c was increased with the increasing the size of cycloalkane rings in 1, 4a, and 4b and the obvious stereos elective effect of the anode nature (C or Pt) being observed in the ca se of dimethoxylation of 4a.