C stereoselectivity

Seebach and coworkers examined the deprotonation/electrophile trapping of phe-nylthioaziridine carboxylates 236 (Scheme 5.58). These thioesters were found to be more stable than their oxy-ester congeners when lithiated treatment of 236 with LDA at -78 °C, followed by trapping with Mel at -100 °C, stereoselectively afforded aziridine 237 [83]. 

Stereoselective Synthesis (Part A) Structure Elucidation (Part A) Stereoselective Synthesis (Part B) Stereoselective Synthesis (Part C) Structure Elucidaton (Part B) Stereoselective Synthesis (Part D) Structure and Chemistry (Part A) Stereoselective Synthesis (Part E) Structure and Chemistry (Part B) Stereoselective Synthesis (Part F) Stereoselective Synthesis (Part G) Stereoselective Synthesis (Part H) Bioactive Natural Products (Part A) Stereoselective Synthesis (Part I) Structure and Chemistry (Part C) Stereoselective Synthesis (Part J) Structure and Chemistry (Part D) Stereoselective Synthesis (Part K) Structure and Chemistry (Part E) Structure and Chemistry (Part F) Bioactive Natural Products (Part B) Bioactive Natural Products (Part C) Bioactive Natural Products (Part D) Bioactive Natural Products (Part E) Bioactive Natural Products (Part F) Bioactive Natural Products (Part G) Bioactive Natural Products (Part H) Bioactive Natural Products (Part I)... 

The /L5-phosphanes with R2 other than H are more stable and undergo decomposition at 20 to 55 C stereoselectively. 

Whereas an allylsilane can serve as an allyl anion synthon, the reaction of 1,3-bis(silyl)propene with electrophiles can afford the 1,3-disubstituted propene. Thus, treatment of a mixture of (If)- and (Z)-2-aryl-l,3-bis(trimethylsilyl)propenes 5 with 2 equivalents of NBS at —78 °C stereoselectively yields the corresponding (Z)-2-aryl-l,3-dibromopropene 6. When 1 equivalent of NBS is employed, the monobromo product 7 is obtained (equation 5). The reactions apparently proceed via the pattern of sequential displacement of allylsilane moieties40,41. 

Scheme 110 c -Stereoselective synthesis of [S-lactams by catalytic systems... 

Avery, M. A. Chong, W. K. M. Jennings-White, C. Stereoselective total synthesis of (+)-artemisinin, the antimalarial constituent of Artemisia annua L. /. Am. Chem. Soc. 1992,... 

Banfi, L, Cardani, S, Potenza, D, Scholastico, C, Stereoselective synthesis of t-butyl 2-amino-2,5-dideoxy-L-/yxo-pentanoate formal synthesis of L-daunosamine, Tetrahedron, 43, 2317-2322, 1987. 

Nasaraka, K, Pai, F-C, Stereoselective reduction of (3-hydroxyketones to 1,3-diols. Highly selective 1,3-asymmetric induction via boron chelates. Tetrahedron, 40, 2233-2238, 1984. 

Xu, Y.-C., Kohiman, D. T., Liang, S. X., Erikkson, C. Stereoselective, Oxidative C-C Bond Coupling of Naphthopyran Induced by DDQ Stereocontrolled Total Synthesis of Deoxyfrenolicin. Org. Lett. 1999,1,1599-1602. 

A useful and practical version of the above protocol involves a catalytic process in which the enone, a bromoallyl silane, cesium carbonate and diisobutyl telluride react in a one-pot procedure to give the desired cyclopropanes with a high c -stereoselectivity. 

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