MNDO and PM3 Study and Regioselectivity of Alkylation of Lithium Derivatives of 1,3,3-Trisubstituted Propynes

P.I. Dem'yanov, G. Boche

Abstracts of the Second International Conference on the Chemistry of the Alkali and Alkaline Earth Metals. Erlangen, Germany. September 17-20, 1997

ABSTRACT. Allenyl and propargyl type structures, respectively, of the unsolvated lithium derivatives 1,3,3-triphenylpropyne (1-Li), 1-(2-methoxyphenyl)-3,3-diphenylpropyne (2-Li) and 9-[2-(2-methoxyphenyl)ethynyl]fluorene (3-Li), their bis-solvated derivatives 1(2,3)-Li—2Et2O and 1(2,3)-Li—2H2O, as well as the structures of the anions 1(2,3) were calculated by MNDO and PM3. The calculated structures of 1-Li—2Et2O and 2-Li—2Et2O are compared with earlier determined X-ray structures.
Spectroscopic investigations (UV-Vis and 13C nmr) reveal contact ion character of 1(2,3)-Li in diethyl ether, while solvent separated ion pairs are formed in THF. Furthermore, the regioselectivities observed in the alkylation reactions of the different ion pairs of 1-Li and 2-Li were determined and correlated with calculated electron density distributions.

Laboratory of Physical Organic Chemistry