, 304 (1979). The dilithiuin derivatives of the ditertiary 1,2-diols, cis-and rrar~s-1,2-dirnethyl-l,2-~yclo-hexanediol, fail to undergo base-induced stereochemical equilibration under conditions that lead to such equilibration uith the dilithiurn derivatives of the disecondary 1,2-diols, cis-and rrnns-l,2-cyclohexanediol. This casts doubt on the proposal that the latter equilibration proceeds by c a r b o n~a r b o n bond cleavage of the dialkoxide to give a diketyl intermediate. It is highly probable that it involves oxidation-reduction as established by Doering in the case of monohydric alcohols. Examination of steroidal secondary-tertiary 1,'-diols under similar conditions shows that such systems can epimerize at both carbinol centres; this is interpreted in terms of sequential oxidation, rr-ketol rearrangement, and reduction. CLARKE E. SLE\IOI\' et PETER YATES. Can. J. Chem. 57, 304 (1979) Les derives dilithies des diols-1,2 ditertiaires, cis-et trans-dimethyl-1, cyclohexanediols-1,2 ne subissent pas d'equilibrations stereochimiques induites par les bases dans des conditions qui permettent de telles equilibrations avec les derives dilithies des diols-1,' disecondaires, cis-et truns-cyclohexanediols-1,2. Ces resultats jettent un doute sur la proposition a l'effet que la del-niere equilibration se produit par I'intermediaire de la rupture de la liaison carbonecarbone du dialcoolate conduisant a un intermediaire dicetyle. II est tres probable que cette reaction implique une oxqdo-reduction du type propose par Doering dans le cas des monoalcools. Un examen de diols-1,2 steroidaux secondaire-tertiaire dans des conditions semblables n~ontre que de tels systemes s'epirnerisent au niveau des deux centres carbinoliques; on interprete ces resultats en termes d'une oxydation sequentielle, d'une transposition u-cetolique et d'une reduction.[Traduit par le journal]
Intoductionshows a variable induction period depending upon ~h~ mechallism by ,.,,hich secondary alkali metal the extent of exclusion of oxidizing impurities. alkoxides epimerire has been thorounhly examined Moreover, it has been observed that heating alkox-(1, 2). ~h~ results are accounted-for by a reac-ides racemizes asymmetric centres u to the carbinol tion sequence (Scheme 1) wherein the substrate is carboll if bear a h~drogell Such data conform with the proposed lnechailisms in which the arrested. Alternatively, by the addition of a mixture of fluorenone and fluorenol, one a facile hydride slowly oxidized by solvellt illlpurities or atmos-acceptor and the other a facile hydride donor, such pheric oxygen to form a quantity of the stereocl~einically hindered substrates as u-and Pcorresponding carbonyl compoulld, slnall alnounts fenchol, which were inert under other conditions, of this hydride acceptor are sufficient to prime a could be e~imerized. chain of hydride transfers between substrate moleIn 1970 Schlosser Weis (3) reported the Gules that eventually in complete stereo-stereochemical equilibration of the dilithium derivachemical equilibration.tive...
