Ch_322b_19.03

Ch_322b_19.03 - H and exploiting the greater acidity of...

Info iconThis preview shows pages 1–5. Sign up to view the full content.

View Full Document Right Arrow Icon
Variations of the Claisen Condensation Reaction The Dieckmann Condensation (1894): An Intramolecular Claisen Condensation Walter Dieckmann (1869-1925), Hamburg, Germany, developed a useful intramolecular variation of the Claisen condensation in the 1890s. CH 2 CH 2 CH CO 2 C 2 H 5 CH 2 C OC 2 H 5 O - Na + CH 2 CH 2 CH 2 CO 2 C 2 H 5 CH 2 CO 2 C 2 H 5 diethyl adipate + NaOEt CH 2 CH 2 CHCO 2 C 2 H 5 CH 2 CO 2 C 2 H 5 : - Na + + EtOH CH 2 CH 2 CHCO 2 C 2 H 5 CH 2 C-OC 2 H 5 - Na + intramolecular acyl addition O =
Background image of page 1

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

View Full Document Right Arrow Icon
CH 2 CH 2 CH CO 2 C 2 H 5 CH 2 C OC 2 H 5 O - Na + cleavage CH 2 CH 2 CH CO 2 C 2 H 5 CH 2 C=O + NaOEt fast deprotonation CH 2 CH 2 C: - CO 2 C 2 H 5 CH 2 C=O Na + + EtOH workup CH 2 CH 2 C: - CO 2 C 2 H 5 CH 2 C=O Na + H + CH 2 CH 2 CH CO 2 C 2 H 5 CH 2 C=O ethyl 2-oxocyclopentanecarboxylate
Background image of page 2
The Crossed Claisen Condensation The condensation reaction of one ester with a second ester, or with an aldehyde or ketone is called a crossed Claisen . As with the crossed aldol condensation, it is a synthetically useful reaction only when it is directed towards one product. The reaction may be directed by: using two different esters where only one has enolizable H. reacting an an ester with aldehydes or ketones with enolizable
Background image of page 3

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

View Full Document Right Arrow Icon
Background image of page 4
Background image of page 5
This is the end of the preview. Sign up to access the rest of the document.

Unformatted text preview: H and exploiting the greater acidity of these compounds. Examples of Crossed Claisen Reactions COC 2 H 5 O = + CH 3 CO 2 C 2 H 5 ethyl benzoate (no enolizable H) (i) NaOEt/EtOH (ii) H + C-CH 2 CO 2 C 2 H 5 O ethyl 3-oxo-3-phenylpropanoate H-COC 2 H 5 O = ethyl formate (no enolizable H) + CH 3 CO 2 C 2 H 5 (i) NaOEt/EtOH (ii) H + C-CH 2 CO 2 C 2 H 5 O H ethyl 3-oxopropanoate CCH 3 O acetophenone (pK a 22) ~ ~ + CH 3 CO 2 C 2 H 5 (i) NaOEt/benzene (ii) H + (pK a = 25) CCH 2 CCH 3 O O 1-phenyl-1,3-butanedione via preferentially formed enolate anion of acetophenone: CCH 2-O + CH 3 C-OC 2 H 5 O Quiz 19.03 Provide two ways to prepare the diketone below by a crossed-Claisen reaction. C 6 H 5 CCH 2 CCH 3 O = O C 6 H 5 COEt O + CH 3 CCH 3 O NaOEt C 6 H 5 CCH 3 O EtOCCH 3 O + NaOEt...
View Full Document

{[ snackBarMessage ]}

Page1 / 5

Ch_322b_19.03 - H and exploiting the greater acidity of...

This preview shows document pages 1 - 5. Sign up to view the full document.

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