REACTIVITY OF UNSATURATED SUBSTRATES UNDER REDUCTIVE ELECTRON-TRANSFER CONDITIONS .1. REDUCTION OF 1,2,3-TRIPHENYL-1H-INDENE WITH SODIUMMETAL IN VARIOUS SOLVENTS
S. Gotta et al., REACTIVITY OF UNSATURATED SUBSTRATES UNDER REDUCTIVE ELECTRON-TRANSFER CONDITIONS .1. REDUCTION OF 1,2,3-TRIPHENYL-1H-INDENE WITH SODIUMMETAL IN VARIOUS SOLVENTS, Perkin transactions. 2, (1), 1994, pp. 151-155
The reduction of 1,2,3-triphenyl-1H-indene 1 with sodium metal in vari
ous solvents was carried out in order to compare the results with thos
e previously obtained in the electrochemical reduction of 1 (Hg cathod
e, dimethylformamide, Bu4N+ClO4- as supporting electrolyte). The most
general reaction observed was reduction of the double bond of the pent
atomic cycle to afford the corresponding indanes of different configur
ations. In two cases (1,2-dimethoxyethane, dioxane) this reaction was
accompanied by reduction of the C(1)-H bond of 1 with formation of the
corresponding anion and hydrogen. No rearrangement or cleavage of gro
ups was observed. In a protic solvent (pentan-1-ol) the results are co
nsistent with a reduction process occurring via protonation of the rad
ical anion of 1, affording quantitatively the isomeric indanes with a
slight preference for those of cis-configuration around the C(2)-C(3)
bond. In liquid ammonia, in contrast, the results are indicative of a
reduction process occurring via protonation of dianionic species, lead
ing to the almost exclusive formation of indanes of trans-configuratio
n around the C(2)-C(3) bond. The self-protonation reaction, which is t
he characteristic process of reduction of 1 under electrochemical cond
itions in the absence of specific proton donors, was found to be follo
wed only in the case of tetrahydrofuran, where a pseudo-unimolecular d
ecay of a paramagnetic species, likely the radical anion of 1, could b
e followed in an EPR cavity.