[4 + 2] Cycloaddition reactions catalyzed by a chiral oxazaborolidinium cation. Reaction rates and diastereo-, regio-, and enantioselectivity depend on whether both bonds are formed simultaneously

Organic Letters

Volumn 12, Issue 5, 2010, Pages 1024-1027

  Mukherjee, Santanu ^a   Corey, E J ^a  

^a HARVARD UNIVERSITY   (United States)

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EID: 77749298284     PISSN: 15237060     EISSN: 15237052     Source Type: Journal    
DOI: 10.1021/ol100032u     Document Type: Article

References (17)

1. Corey, E. J. Angew. Chem., Int. Ed. 2009, 48, 2100-2117.
2. The very potent Lewis acid 1 can be generated in situ from the corresponding oxazaborolidine (available from. Sigma-Aldrich Co.) simply by addition of triflimide.
3. Ryu, D. H.; Zhou, G.; Corey, E. Org. Lett. 2005, 7, 1633-1636.
4. Also see: Ryu, D. H.; Zhou, G.; Corey, E. J. J. Am. Chem. Soc. 2004, 126, 4800-4802.
5. For a report on chiral auxiliary-controlled diastereoselective Diels-Alder reactions of unsymmetrical maleates, see: Maruoka, K.; Akakura, M.; Ooi, T.; Yamamoto, H.J. Am. Chem. Soc. 1994, 116, 61536158.
6. °C and found to be complete within 15 h. For the determination of ee and absolute configuration see Supporting Information.
7. Ryu, D. H.; Corey, E. J. J. Am. Chem. Soc. 2003, 125, 6388-6390.
8. Two diastereomers were formed at a ratio of >20:1 with or without the catalyst 1. For further details see Supporting Information.
9. Under the same reaction conditions using (E)-cyano trifluoroethyl ester as the substrate, two diastereomeric products were obtained in. 3.5:1 ratio with 42% and 15% ee, respectively. Product derived from (Z)-cyano trifluoroethyl ester was obtained in 6:1 endo/exo ratio with. 62% ee for the endo diastereomer.
10. Vinyl boronate 23 was prepared by Cu-catalyzed addition of is(pinacolato)diboron to ethyl propiolate. Lee, J.-E.; Kwon, J.; Yun, J. Chem. Commun. 2008, 733-734.
11. For a catalytic enantioselective Diels-Alder reaction of vinyl boronate and it application in total synthesis of (+)-paniculide A, see: Yamamoto, I.; Narasaka, K. Bull. Chem. Soc. Jpn. 1994, 67, 3327-3333.
12. Miyaura, Y.; Yamamoto, Y. In Comprehensive Organometallic Chemistty III; Mingos, D. M. P., Crabtree. R. H., Eds.; Elsevier: London, 2007; Vol. 9, pp 145-244.
13. For other approaches to this type of chiral norbornadiene, see: (a) Brown, M. K.; Corey, E. J. Org. Lett. 2010, 12, 172-175.
14. (b) Payette, J. N.; Yamamoto, H. Angew. Chem., Int. Ed. 2009, 48, 8060-8062.
15. For a recent report on asymmetric Diels-Alder reactions of substituted cyclopentadiene, see: Payette, J. N.; Yamamoto, H. J. Am. Chem. Soc. 2007, 129, 9536-9537.
16. In this regard ethyl acrylate, 1, and cyclopentadiene do not react at -78 °C in contrast to diethylfumarate, 1, and cyclopentadiene.
17. For a recent application of chiral cationic oxazaborolidines, see: Mukherjee, S.; Corey, E. Org. Lett. 2010, 12, 632-635.