Ch_322b_19.04

Ch_322b_19.04 - a ~ 11) are produced in stoichiometric...

Info iconThis preview shows pages 1–3. Sign up to view the full content.

View Full Document Right Arrow Icon
Alkylation of Enolate Anions The introduction of alkyl groups and formation of C-C bonds is called alkylation . This very fundamental process in organic synthesis can be carried out, in principle, by reacting a carbanion with an alkylating agent such as R'-X. Two general alkylation methodologies are: (1) Very strong bases are used to produce stoichiometric amounts of carbanions (often simple enolate anions) in aprotic solvents. These carbanions are then alkylated in a second step. LDA (lithium diisopropylamide) is a standard strong base used in this alkylation procedure. (2) The enhanced acidity of 1,3-dicarbonyls is exploited to produce stoichiometric amounts of relatively stable enolate anions in solvents such as ethanol using bases such as ethoxide. These enolate anions are then alkylated in a second step. R-H + B: - (-B-H) R: - carbanion R'-X alkylation R-R'
Background image of page 1

Info iconThis preview has intentionally blurred sections. Sign up to view the full version.

View Full DocumentRight Arrow Icon
Formation of Enolate Anions of 1,3-Dicarbonyl Compounds The enolate anions of 1,3-dicarbonyl compounds (pK
Background image of page 2
Background image of page 3
This is the end of the preview. Sign up to access the rest of the document.

Unformatted text preview: a ~ 11) are produced in stoichiometric amounts by reaction with alkoxide bases. C O = CH 2 O C pK a ~ ~ 11 + NaOEt C O CH O C :-Na + + EtO H pK a = 16 stoichiometric concentration essentially complete reaction Alkylation of the Enolate Anion After formation of one full equivalent of the enolate anion, one equivalent of an alkylating agent (RX) is added: C O CH O C-Na + + R-X S N 2 C O C O C H R + NaX alkylated product Two 1,3-dicarbonyl compounds that are classic examples of the synthetic applications of this chemistry are: Two standard syntheses developed many years ago that exploit the extraordinary stability of enolate anions derived from 1,3-dicarbonyl compounds are: C O = CH 2 O C CH 3 C 2 H 5 O ethyl acetoacetate (pK a = 10.7) C O CH 2 O C C 2 H 5 O C 2 H 5 O diethyl malonate (pK a = 12.9) (1) The acetoacetic ester synthesis of substituted acetones (2) The malonic ester synthesis of substituted acetic acids...
View Full Document

This note was uploaded on 10/20/2009 for the course CHEM 322BL at USC.

Page1 / 3

Ch_322b_19.04 - a ~ 11) are produced in stoichiometric...

This preview shows document pages 1 - 3. Sign up to view the full document.

View Full Document Right Arrow Icon
Ask a homework question - tutors are online