Electroreductions and Oxidative Dimerizations

It proved possible to modify retinoids by electrolytic reductions. However, the few examples disclosed hitherto do not show any advantages over the conventional methods of preparative organic chemistry. Retinyl acetate (9) was reduced to axerophthene (568) in very good yield at a potential of —2.0 V in dimethylfor- 

The electroreduction of A -retinylidene-n-butylamine (91) in a mixture of acetonitrile, dimethylformamide, and water has been investigated. In a two-electron process, (91) was converted to the dihydroenamine (92) (Stutts et al.y 1981). 

When (91) was employed in dry dimethylformamide, it was possible to detect the radical-anion (615 nm) and the dianion (550 nm). 

Methyl retinoate (43) was hydrogenated at the double bond in a cathodic reduction reaction under kinetic control to give (93) (Terem and Utley, 1979). 

Protonated (91) was reduced in a one-electron process in acetonitrile, the radicals formed undergoing rapid dimerization. The reductive electrodimerization of retinaldehyde (2) in the presence of carbon acids such as diethyl malo-nate, led, in a one-electron process, to the 40 pinacol (94), which is of course of interest as an intermediate for the synthesis of p-carotene (Sioda et al., 1976 Powell and Wightman, 1979). With phosphorus triiodide, (94) gave p-carotene. 

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