D H Ripin& D A. Evans Elimination reactions of selenoxides Chem 115 The selenoxide elimination reaction The first example: Jones, Chem. Commun 1970, 86. General Selenium References elenium in Natural Products Synthesis, K C Nicolaou, N. A Petasis Organoselenium Chemistry, D. Liotta, 1987 Wiley-Interscience Selenium Reagents and Intermediates in Organic Synthesis, C. Paulmier @1986 Pergamon Press Functionalization of olefins 20°C→40°C PhSe-X -PhSeoH By comparison X=OAC OH. CN. CL Br 80c→130°c Sharpless, J. Org. Chem. 1974, 39, 429 州H| PhSOH The selenoxide elimination is usually two ste A. Selinide formation Nucleophilic Selenium Reagents RSeCN or RSe SeR and NaBH4, RSeM, RSeH (with Lewis Acid) Chapter 4, Organoselenium Chemistry, D. Liotta, 1987 Wiley-Interscience Electrophilic Selenium Reagents Tomoda. Chem. Commun 1982, 871; Tet. Lett 1982, 23, 1361 RSeCl, RSeBr, RSe(O)Cl, RSeSeR, alkyl selenium succinimide, RSeSO2Ar Chapter 1, Organoselenium Chemistry, D. Liotta, 1987 Wiley-Interscience Epoxide Ring Opening-Refunctionalization a Some useful oxidizing agents H202, MCPBA, RCOOOH, NaIO4, O3,(t-BuO)2, Th" Nitrate, NCS or NBS/H20 PhSe-SePh Chapter 5, Selenium Reagents and Intermediates in Organic Synthesis, C Paulmier, 1986 Pergamon Press 27A-05-Selenoxide elim-1 12/6/93 11: 00 AM Both of the above reactions have been heavily exploited in synthesis
Tomoda, Chem. Commun 1982, 871; Tet. Lett 1982, 23, 1361 PhSeCN ∆ [Ox] ■ Functionalization of Olefins: Sharpless, J. Org. Chem. 1974, 39, 429. 3 <1 2 49 97 99 98 51 OAc OH OMe Cl Chapter 5, Selenium Reagents and Intermediates in Organic Synthesis, C. Paulmier,1986 Pergamon Press. Chapter 4, Organoselenium Chemistry, D. Liotta, 1987 Wiley-Interscience. RSeCN or RSeSeR and NaBH4, RSe-M+, RSeH (with Lewis Acid) Chapter 1, Organoselenium Chemistry, D. Liotta, 1987 Wiley-Interscience. RSeCl, RSeBr, RSe(O)Cl, RSeSeR, alkyl selenium succinimide, RSeSO2Ar, ... H2O2, MCPBA, RCOOOH, NaIO4,, O3, (t-BuO)2, ThIIINitrate, NCS or NBS/H2O ■ Some useful oxidizing agents: ■ Electrophilic Selenium Reagents: ■ Nucleophilic Selenium Reagents: The selenoxide elimination is usually two steps: A. Selinide formation B. Oxidation & elimination. Selenium in Natural Products Synthesis, K. C. Nicolaou, N. A. Petasis Organoselenium Chemistry, D. Liotta, 1987 Wiley-Interscience. Selenium Reagents and Intermediates in Organic Synthesis, C. Paulmier, © 1986 Pergamon Press. General Selenium References: -20˚C → 40˚C D. H. Ripin & D. A. Evans Elimination Reactions of Selenoxides Chem 115 + The Selenoxide Elimination Reaction + ‡ By comparison: ‡ + + 80 ˚C → 130˚C -PhSeOH -PhSOH 20˚C The first example: Jones, Chem. Commun 1970, 86. O3 + PhSe–X [Ox] ∆ X Ratio X = OAc, OH, CN, Cl, Br, + X– ■ Epoxide Ring Opening-Refunctionalization: PhSe–SePh NaBH4 [Ox] Both of the above reactions have been heavily exploited in synthesis SePh CN Me Se H H Se Me Se–Ph Me H Ph–Se H R R H H O– R H H R X X Ph H H Ph OXSePh O SePh OH OH Se O H H R R H Ph S Ph H O R R H H R H H R Ph–S O– H H R R H CN 27A-05-Selenoxide elim-1 12/6/93 11:00 AM
D H Ripin& D A. Evans Elimination reactions of selenoxides Chem 115 Synthetic Applications Functionalization of olefins. Ph PhSecl 0°C OTBS i Phse cf(omer Raucher Tet. Lett. 1979. 3057 Me Seph cI H202 OTBS This is kinetic product at BF3oEt2 Aco PhseOH NaHco CoH13 SePh [Ox Raucher. Tet Lett 1977. 3909 PhSe-sO2Ph SOpH Rollin Synthesis 1984, 134 SePh These ns are quite valuable in setting up Claisen rearrangements Mooch OTBDPS 25℃c DBU, xylene,↑↓ EtO2C OTBDP Metz. Tet Lett 1982. 23. 4067 (+)-Laurencin Holmes j Am. chem. soc. 1993. 115 10400 27A-06-Selenoxide elim-2 127/93 12: 02 PM
free radical addn Rollin Synthesis 1984, 134. ∆ NaIO4 NaHCO3 83% 85% BF3OEt2 55% [Ox] Raucher Tet. Lett. 1979, 3057. H+ steps 25 °C DBU, xylene, ↑↓ Holmes J. Am. Chem. Soc. 1993, 115, 10400. NaIO4 NaHCO3 73% (+)-Laurencin Metz, Tet. Lett 1982, 23, 4067 [Ox] ∆ PhSeBr CH2=CHOEt hν PhSe-SO2Ph ∆ [Ox] Kice, Tet. Lett 1980, 21, 4155 Raucher, Tet. Lett 1977, 3909 [Ox] ∆ PhSeBr MeCN This is kinetic product at lower temperatures Beau, JACS, 1983, 105, 621 pyr H2O2 Cl– 0 °C PhSeCl ■ Functionalization of Olefins: + Synthetic Applications D. H. Ripin & D. A. Evans Elimination Reactions of Selenoxides Chem 115 These rxns are quite valuable in setting up Claisen rearrangements O O OTBDPS SePh O O OTBDPS H OAc O Et Br H OTBDPS O O OH Me CO2Me Me PhSe C(OMe)3 SePh Me Me Me OTBS OTBS Me CO2Me O OAc AcO AcO PhSe OH AcO AcO O O SePh O O AcO AcO AcO AcO O Me SePh Cl SePh Me OTBS Me Me OTBS Me Br Cl SePh C6H13 C6H13 C6H13 SePh Br SO2Ph Ph Ph Ph SO2Ph OH H MeOCH2 Br OEt PhSe MeOCH2 H O OEt SePh EtO2C CHO H MeOCH2 27A-06-Selenoxide elim-2 12/7/93 12:02 PM