Inter- and intramolecularhetero diels-alder reactions, XXI. Intramolecularhetero diels-alder reaction of alkylidene-1,3-dicarbonyl compounds. Experimental evidence for an asymmetric transition state
✍ Scribed by Tietze, Lutz F. ;Brumby, Thomas ;Brand, Siegbert ;Bratz, Matthias
- Publisher
- Wiley (John Wiley & Sons)
- Year
- 1988
- Tongue
- English
- Weight
- 784 KB
- Volume
- 121
- Category
- Article
- ISSN
- 0009-2940
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✦ Synopsis
The intramolecular hetero Diels-Alder reaction of heterodienes 13 is described. The heterodienes, which are obtained in situ by Knoevenagel condensation of aldehydes 129 -e with dimethylbarbituric acid (2), yield the cycloadducts 14a-e/15a-e and the ene adducts 169, c-e/17a, c-e. The ratio of 14/15 was determined by HPLC. The resulting data are interpreted as experimental evidence of an asymmetrical transition state of the Diels-Alder reaction.
For this reason we investigated the tandem Knoevenagelhetero-Diels-Alder reaction of aldehydes 12 and dimethylbarbituric acid (2).
Results
The synthesis of the aldehydes 12a-e was accomplished through Wittig reaction"' of forrnylester 8 with the phosphoniurn salts 9a-e to give the unsaturated esters 1Oa-e,