Diels-Alder reactions of N-tosyl-3-nitroindole and dienamides: Synthesis of intermediates of Aspidospermine alkaloids

Tetrahedron Letters

Volumn 40, Issue 17, 1999, Pages 3343-3346

  Biolatto, Betina ^a   Kneeteman, María ^a   Mancini, Pedro ^a  

^a UNIVERSIDAD NACIONAL DEL LITORAL   (Argentina)

Author keywords

[No Author keywords available]

Indexed keywords

1,3 BUTADIENE DERIVATIVE; ASPIDOSPERMINE; INDOLE DERIVATIVE; N TOSYL 3 NITROINDOLE; UNCLASSIFIED DRUG;

ARTICLE; CHEMICAL STRUCTURE; REACTION ANALYSIS; RELIABILITY; STEREOCHEMISTRY; SYNTHESIS; TEMPERATURE SENSITIVITY;

EID: 0033597277     PISSN: 00404039     EISSN: None     Source Type: Journal    
DOI: 10.1016/S0040-4039(99)00511-0     Document Type: Article

References (13)

1. 1 O. Diels, K. Alder, Liebigs Ann. Chem. 1928, 460, 98.
2. 2 Wenkert showed for the first time that indoles can act as dienophiles in D-A reactions with simple nucleophilic dienes, when 3-substituted with electron-withdrawing groups and N-substituted with a powerful electron-withdrawing function. In order to attain good yields, these cycloaddition reactions have to be performed under high temperatures (over 150°C), showing poor regioselectivity. E. Wenkert, P. Moeller, S. Piettre, J. Am. Chem. Soc. 1988, 110, 7188-7194.
3. 3 W. Oppolzer, L. Bieber, E. Francotte, Tetrahedron Lett. 1979, 4537-4540.
4. 4 W. Oppolzer, W. Frostl, Helv. Chim. Acta 1975, 58, 587-589.
5. 2).
6. 2C=CH-CH=); 7.3 (d, 1H, CH=CH-N-, J= 8 Hz). The diene 2b was obtained following the same procedure.
7. 7 General procedure for thermal D-A reactions: an ampoule containing 0.5 mmol of the dienophile, 1.5 mmol of diene in 0.5 ml of benzene was cooled in liquid nitrogen, sealed and then heated in a silicon bath at the required temperature and time. It was then cooled once more in liquid nitrogen, opened, evaporated and the residue chromatographed (silica gel, hexane/ethyl acetate).
8. H 7.23-7.41).
9. ipso-Me).
10. tosyl), 171,6 (C=O).
11. 11 Despite the expenditure of much effort on the isolation of a 4-unsubstituted N-tosyl-dihydrocarbazole or the 4-(N-acyl-N-alkylamino)-substituted carbazole from these reactions, none was observed in any case.
12. 12 Attempts to obtain the D-A adduct from the reaction of 1-(N,N-diethylamino)-1,3-butadiene and N-tosyl-3-nitroindole at 50°C in a close ampoule led to the complete decomposition of the diene and 50% detosylation of the dienophile, obtaining N,N-diethyl-4-toluensulfonamide (unpublished results).
13. 13 In contrast, the higher temperature requirements for the cycloaddition of N-tosyl-3-acetylindole (comparatively less reactive than 3-nitroderivative) and the thermal instability of both 1-(N-acyl-N-alkylamino)-1,3-butadienes, makes this combination unsuitable for the pursued objective (unpublished results).