Potentially synthetically useful reactions of the dilithium salts of the title dianions have been investigated. Electrophilic quenching with a variety of reagents usually leads to the expected products in good yield. Quenching the diphenylacetone dianion with 1 equiv of trimethylchlorosilane, however, gives a good yield of 1,3-diphenylallene obtained by formal elimination of a trimethylsiloxy anion from an intermediate monoquenched monoanion salt. NMR studies, however, do not reveal the intermediacy of the 1,3-diphenyl-2-(trimethylsiloxy)allyl anion but rather suggest that the initial reaction site is at carbon, rather than oxygen. Oxidation of the dianions leads either to ring closure or dimerization for the tribenzylidenemethane dianion and to dimerization for the diphenylacetone dianion. The dimerization reactions are stereospecific, both with respect to the two new stereocenters produced and for the double bonds of the bis-silyl enol ether products if the dimeric bis-enolate dianion products are quenched with trimethylchlorosilane.
reactions of organo-metal compounds reactions of organo-metal compounds O 0350 -083Reactions of the Lithium Salts of the Tribenzylidenemethane Dianion, Diphenylacetone Dianion, and Related Compounds.-Various Y-conjugated dilithium salts of the title dianions, e.g. (II) and (XIII), are easily prepared by metalation of the corresponding olefin and isolated as crystalline adducts with two molecules of TMEDA. Electrophilic quenching with a variety of reagents, e.g. (III), (V), and (IX), usually leads to the expected products in good yields. The quenching reaction between dianion (XIII), derived from acetone (XII), and TmsCl are unusual. Excess of TmsCl leads to Z-configurated disilylated compound (XVI). The reaction with 1 equivalent TmsCl gives allene (XV) in good yield. Oxidation of the dianions with dibromoethane in hexane or THF leads for the tribenzylidenemethane dianions either to ring closure, e.g. (XVII), or dimerization and for the diphenylacetone dianion to dimerization. When the intermediate dimeric enolate derived from the oxidation of (XIII) is quenched with TmsCl, only (Z,Z) and (E,E) isomers (XVIII) and (XIX) are observed; the (E,Z) isomer is not formed. -(WITT, O.; MAUSER, H.; FRIEDL, T.; WILHELM, D.; CLARK, T.; J. Org. Chem. 63 (1998) 4, 959-967; Inst. Org. Chem., Friedrich-Alexander-Univ., D-91054 Erlangen, Germany; EN)
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