STATE IN SOLUTION, STRUCTURE, AND REGIOSELECTIVITY OF REACTIONS OF THE LITHIUM 1-(2-METHOXYPHENYL)-3,3-DIPHENYLPROPYNE DERIVATIVE

According to the spectrophotometric data, the lithium 1-(2-methoxyphen yl)-3,3-diphenylpropyne derivative in diethyl ether exists as contact ion pairs, while in THF, according to the spectrophotometric and C-13 NMR data, solvent-separated ion pairs are predominantly formed. Accord ing to the C-13 NMR data, the carbanion in the solvent-separated ion p airs has a structure close to the propargylic type. The regioselectivi ty of reactions of the lithium derivative with ethyl halides in diethy l ether, THF, and hexamethyphosphoramide, with benzyl chloride in the first two solvents, and with methanol in THF were studied. The protona tion with methanol proceeds exclusively at the allenylic center (C-l) while the ethylation and especially benzylation proceed predominantly at the propargylic center (C-3). The selectivity of ethylation of the propargylic center of both solvent-separated ion pairs in THF and cont act ion pairs in diethyl ether increases as the hardness of the ethyla ting agent increases, and in the case of the same ethyl halide, the se lectivity increases from the solvent-separated ion pairs to the contac t ion pairs. The spectral data obtained and the data on changes in the regioselectivity do not allow one to believe that the contact ion pai rs of the lithium derivative in ether exhibit the intramolecular coord ination of the lithium cation to the methoxy group, which might lead t o the allenylic structure of contact ion pairs of this derivative.