Rhodium-catalyzed propargylic substitution: A divergent approach to propargylic and allenyl sulfonamides

Angewandte Chemie - International Edition

Volumn 45, Issue 30, 2006, Pages 4970-4972

  Evans, P Andrew ^a   Lawler, Michael J ^a  

^a INDIANA UNIVERSITY   (United States)

Author keywords

Allenes; Carbocyclization; Isomerization; Rhodium; Sulfonamides

Indexed keywords

AMINATION; AMINES; CATALYSIS; ISOMERIZATION; RHODIUM; SUBSTITUTION REACTIONS; SYNTHESIS (CHEMICAL);

ALLENES; CARBOCYCLIZATION; SULFONAMIDES; SYNTHETIC UTILITY;

SULFUR COMPOUNDS;

EID: 33746718799     PISSN: 14337851     EISSN: None     Source Type: Journal    
DOI: 10.1002/anie.200600615     Document Type: Article

References (27)

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5. b) Ru: Y. Nishibayashi, Y. Inada, M. Hidai, S. Uemura, J. Am. Chem. Soc. 2003, 125, 6060-6061;
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19. 4), filtered, and concentrated in vacuo to afford a crude oil. Purification by flash chromatography (ethyl acetate/hexanes 5:95) furnished the propargylic sulfonamide 2a (86.4 mg, 82 %) as a colorless oil.
20. Interestingly, this transformation does not allow the chirality transfer observed with the analogous allylic substitution; for example, treatment of the enantiomerically enriched propargylic carbonate (S)-1a (85 % ee) under the optimized reaction conditions, furnished propargylic sulfonamide 2a in 75 % yield as the racemate (0 % ee).
21. Treatment of the propargylic sulfonamide 2m with the lithium anion of the N-benzyl p-toluenesulfonamide furnished the 1,1-disubstituted allene 3m in 99 % yield, thus clearly demonstrating that the rhodium catalyst is not involved in the isomerization. For a similar process that involves a mixed catalyst, see: M. D. Milton, Y. Inada, Y. Nishibayashi, S. Uemura, Chem. Commun. 2004, 2712-2713.
22. For a recent review on single-pot catalysis with the same metal-complex, see: A. Ajamian, J. L. Gleason, Angew. Chem. 2004, 116, 3842-3848;
23. Angew. Chem. Int. Ed. 2004, 43, 3754-3760.
24. For recent examples of sequential rhodium-catalyzed allylic substitution/carbocyclization, see: a) P. A. Evans, J. E. Robinson, J. Am. Chem. Soc. 2001, 123, 4609-4610;
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26. The excellent selectivity for the rhodium-catalyzed [4+2] cyclo-addition with the allene versus the alkyne moiety to afford 5 rather than 6, respectively, is feasible as the alkyne carbocyclization requires higher temperature (60°C).
27. For an example of a metal-catalyzed [4+2] carbocyclization reaction with an unactivated allene, see: P. A. Wender, T. E. Jenkins, J. Am. Chem. Soc. 1989, 111, 6432-6434.