Transcription of Ch. 7 - Enolates - Purdue University
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Ch. 7 - Enolates - Purdue University
209 Enolates Enolates are the conjugate anions of carbonyl compounds. Although they have been known and used since the turn of the 20th Century, it was the development of specific Enolates (see below) by H. O. House of MIT in the 1960-1970s that made carbanion chemistry one of the most important tools for stereo- and regio-controlled carbon-carbon bond formation in organic synthesis. That importance continues to this day. Generation of Enolates by deprotonation of carbonyls: OYHB:baseOYOYY=H, alkyl, OR, NR2, SR Relevant acidity data: Compound pKa aldehyde ~20 ketone ~20 cyclic ketone ~17 -dicarbonyl 11-13 ester ~25 nitrile ~25 Compare these pKa s to the basicity values (as conjugate acid pKa s) of common bases: R2N- pKaconj = 35 RO- pKaconj = 16 (R = Me) - 18 R = t-Bu) R3N pKaconj = 9-11 Conclusion: MeOOOMeOpKa = 13 NaOMeMeOH(pKa = 16)MeOOOMeONapKeq = 16-13 = 3 Keq = 103 ONaOMeMeOH(pKa = 16)pKa = 17 ONapKeq = 16-17 = -1 Keq = 10-1 OpKa = 17 OLipKeq = 35-17 = 18 Keq = 1018Li+ -N(i-Pr)2+ HN(i-Pr)2pKa = 35 210 Structure of Enolates A
651.06 209 Enolates Enolates are the conjugate anions of carbonyl compounds. Although they have been known and used since the turn of the 20th Century, it was the development of “specific enolates” (see below) by H. O. House of MIT in the 1960-1970s that made carbanion
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