Abstract
AbstractThe direct dimetallation of vinylacetylene (1‐buten‐3‐yne) at the 2‐ and 4‐positions can be achieved by the butyllithium‐potassium tert‐butoxide reagent, but not when butyllithium is used alone or in the presence of TMEDA. Supporting experimental and calculational (ab initio and MNDO) results suggest that the potassium acetylide, KC≡C‐CH = CH2, is formed first. Further metallation occurs at the activated C‐2 vinyl position. Preferential substitution at the C‐2 position in t‐BuC≡CCH = CHt‐Bu also was demonstrated. Neither dianion nor dilithium models account for the dimetallation results; in both cases, 1,4‐arrangements are indicated to be better than 2,4. The 2,4‐dimetallated vinylacetylene is a useful intermediate allowing the synthesis of derivatives inaccessible otherwise.
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