“Tert‐amino effect” in heterocyclic synthesis. Synthesis of thieno[3,2‐e]indolizines and thieno[2,3‐c]quinolizines
- 1 January 1990
- journal article
- research article
- Published by Wiley in Recueil des Travaux Chimiques des Pays-Bas
- Vol. 109 (9) , 481-484
- https://doi.org/10.1002/recl.19901090907
Abstract
A new and convenient route for the synthesis of the thieno[3,2‐e]indolizines 4a,b,d, the thieno[2,3‐c]quinolizine 4e and their [1]benzothieno analogues 9a,b is presented. Reaction of the (dialkylamino)thiophenes 1, 5 and 7 with (methoxymethylene)malononitrile (2) gives the Michael adducts 3, 6 and 8. Heating of 3 and 8 in refluxing 1‐butanol gives the cyclized products 4 and 9. This cyclization proceeds via a 1,5 hydrogen shift, followed by an intramolecular addition of the carbanion to the iminium double bond in the intermediate 10 formed. The scope and limitations of this approach are discussed.Keywords
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