References and Notes
- Paust , J. 1991 . Pure & Appl. Chem. , 63 : 45
- Isler , O. 1971 . Carotenoids , pp. 431 – 436 . Birkhauser-Verlag .
- Zeller , P. , Bader , F. , Lindlar , H. , Montavon , M. , Müller , P. , Ruegg , R. , Ryser , G. , Saucy , G. , Schaeren , S. F. , Schwieter , U. , Stricker , K. , Tamm , R. , Zürcher , P. and Isler , O. 1959 . Helv. Chim. Acta , 42 : 841 British patent 866, 691 (April 26, 1961)
- Vinylogous ester 4a is now available as an expensive specialty chemical from Aldrich Chemical Co.
- 1963 . Examples of this type of crossed-Claisen condensation can be found in Organic Syntheses, Coll. , Vol. IV , pp 210 and 536 New York : Wiley .
- Powers , J. . , Seidner , R. , Parsons , T. G. and Berwin , H. J. 1966 . J. Org. Chem. , 31 : 2623 This type of decomposition ceases when the alcohol concentration is increased. See:
- To obtain enolate 6 in high yield, it was essential to keep the instantaneous concentration of propionaldehyde low—preferably about 0.001 M. Since enolate 6 is formed irreversibly, at the conclusion of the reaction its concentration can approach 1.0 M
- Villagomez-Ibarra , R. and Joseph-Nathan , P. 1994 . Tetrahedron Lett. , 35 : 4771
- Prior to the alkylation of stabilized enolate 6, excess methyl formate and methyl alcohol were removed by simple distillation. Removal of methanol, while not essential, enabled the alkylation step to proceed more rapidly. The best solvents for this alkylation proved to be polar, aprotic solvents such as acetonitrile, N,N-dimethylformamide, and 1-methyl-2-pyrrolidinone.
- Alkylation of 6 with the less reactive primary alkyl chloride required a longer reaction time (30–40 hours) and a higher temperature (65–70°C).
- Johnson , W. S. and Schneider , W. P. 1950 . Org. Synth. , 30 : 18
- This solution was prepared by addition of small pieces of metallic sodium to methyl alcohol (HPLC-grade). Once hydrogen evolution had ceased, the mixture was allowed to cool to room temperature before adding the methyl formate. An efficient reflux condenser was connected to the reaction flask to minimize loss of the latter volatile reagent.
- This addition was conducted using either a syringe pump or, alternatively, a 10 μL syringe (one 10 μL addition every minute).
- Klimko , V. T. , Protopopova , T. V. , Smirnova , N. V. and Skoldinov , A. P. 1962 . Zh. Obshch. Khim. , 32 : 2961
- The moderate yield in this experiment may arise from the difficulty in separating vinylogous ester 4a from DMF during the reaction workup and/or incomplete alkylation of stabilized enolate 6 at 40°C. In a similar experiment that involved alkylation of enolate 6 with 1-bromopropane at 62°C for 18 hours, an 82% yield of 3-propoxy-2-methylpropenal (4b) was obtained.