Ynolates are carbanions having a triple bond in place of the double bond in enolate anions. Ynolates are ketene anion equivalents, thus ynolates introduce a ketene unit into substrates and the resulting products possess high reactivity. This allows ynolates to undergo unique reaction sequences. For the past 20 years, several methods for the generation of ynolates and their reactions have been developed. Recently, we have developed a novel efficient method for their generation via cleavage of ester dianions. Starting from this success, we have found new reactions of ynolate anions. Ynolate anions react with carbonyl compounds to give β-lactone enolates, which are converted into olefins with high E-selectivity. It is noteworthy that high E-selectivity was achieved in the synthesis of tetrasubstituted olefins. Utilizing the strong nucleophilicity of the β-lactone enolates, we have succeeded in the first tandem [2+2] cycloaddition-Dieckmann condensation to lead synthetically useful 2,3-disubstituted-2-cycloalkenones in good yields. Ynolate anions were found to react with N-sulfonyl aldimines to give β-lactams. N-2-methoxyphenyl aldimines efficiently activate their cycloaddition of lithium ynolates via chelation to give β-lactams and α,β-unsaturated amides. We have demonstrated the high functionality of ynolate anions. Ynolate chemistry has begun and much remains to be discovered.
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