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The dian ionic species, lithium 2-li thio benzofuran -3-carboxylate (5) and lit hi um 3 -lit hiobenzof uran -2carboxylate (11 b) can be readily generated from the parent acids by reaction with lithium diisopropylamide in tetrahydrofuran at low temperatures. While compound ( 5) is a useful synthetic intermediate, which reacts efficiently with a number of electrophiles, (11 b) instead undergoes rapid opening of the furan ring to give (2-hydroxyphenyl)propynoic acid (10a). By contrast, 5and 7methoxybenzofuran-2-carboxylic acids (1 3a) and (13c) give rise to the dianions (14a) and (14c) which are sufficiently stable at < -90 "C to be trapped by aldehydes. The dianion (14b) derived from 6-methoxybenzofuran-2-carboxylic acid (1 3b), however, suffers rapid ring opening before it can be trapped, even at very low temperatures. A plausible explanation of these observations is given. Metallation of 3-methylbenzofuran-2-carboxylic acid (1 8) affords the dianion (20), which cannot

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