C.A. Morales Olefin Addition RXns in Polyether Synthesis-1 Chem 206 One plausible biosynthetic proposal for polyether An alternate biosynthetic proposal natural products (Z, 4, Z)-premonensin triene [2+2] reductive elimination HO2C MeQ HO, C- Me Me Monensin B from lecture 7 cane,D.E.JAcs,1983,105,3394 cane,D.E.JACs,1982,104,7274 Monensin Townsend, C.A.: Basak.A. Tetrahedron 1991. 47 2591
Me O Me Me Et Me O Me HO2C Me OH Me OH H O LnM O R O Me Me Me O Me Me OH [O] Me O Me Et Me Me O Me HO2C Me OH Me OH O H M O R O Me Me Me O Me Me OH O O O Me O Me Me Et Me O Me HO2C Me OH Me OH H O O LnM O O O O O Me MeO Me HO2C HO Me Me Me Me H Me H H H OH Me OH H O O O O O Me MeO Me HO2C HO Me Me Me Me H Et H H H OH Me OH H C. A. Morales Olefin Addition Rxns in Polyether Synthesis-1 Chem 206 One plausible biosynthetic proposal for polyether natural products: Monensin B Cane, D. E. JACS, 1983, 105, 3394. Cane, D. E. JACS, 1982, 104, 7274. An alternate biosynthetic proposal: Townsend, C. A.; Basak, A. Tetrahedron, 1991, 47, 2591. from lecture 7 (Z,Z,Z)-premonensin triene [2+2] Monensin reductive elimination
C.A. Morales Olefin Addition Rxns in Polyether Synthesis-2 Chem 206 A biomimetic model for syn-oxidative polycyclization: But for secondary alcohols -Pr PCC HOAC PCC HOAC 9%combined, 11: 1(trans cis Conformational model for syn-oxidative cyclization HR 38%,99:1 RE OH O OH Rz Does this explain the lower degree of trans-cross-ring" selectivity observed for(Er-olefins? HOAC R 19%combined, 3.7: 1( trans cis reductive RE OH trans-substituted 24%.17:1 tetrahydrofuran High syn-stereospecificity for tertiary alcohols McDonald. F E. JACS. 1994. 116.7921
Me OH Me Me Me Me PCC HOAc Me OH Me Me Me Me PCC HOAc O O H Me Me Me O O O H Me Me Me O OH O O H Me H Me Me Me Me OH O O H Me H Me Me Me Me OH O O H Me H Me Me Me Me OH O O H Me H Me Me Me Me O RS RL H RZ RE OH O Cr H RZ RE RL RS H H O O OH i-Pr OH Me Me Me PCC HOAc O Cr RL RS H H O O OH H RE RZ O Cr RL RS H H O OH H RE RZ O O H i-Pr Me O Me C. A. Morales Olefin Addition Rxns in Polyether Synthesis-2 Chem 206 A biomimetic model for syn-oxidative polycyclization: McDonald, F. E. JACS, 1994, 116, 7921. 9% combined, 11:1 (trans:cis) 38%, 9.9:1 19% combined, 3.7:1 (trans:cis) 24%, 17:1 High syn-stereospecificity for tertiary alcohols But for secondary alcohols... ...simple oxidation occurs more rapidly than oxidative cyclization. Conformational model for syn-oxidative cyclization: [2+2] reductive elimination trans-substituted tetrahydrofuran Does this explain the lower degree of "trans-cross-ring" selectivity observed for (E)-olefins?
C.A. Morales Olefin Addition Rxns in Polyether Synthesis-3 Chem 206 Application of the model for syn-oxidative Application of the model for syn-oxidative polycyclization using an all(2)-polyolefin polycyclization on an all (E)-polyolefin OH (E,E, Er-pregoniocin triene (ZZZ)premonensin triene Et2Zn, Ti(o-+Pr)4 ADmxβ OH Et C12H25 CrO3(py)2 Me 1)AC20, EtaN cat. DMAP HO A Et o 2)NaBH4, CeCl3 n-C12H25(Cl2CHCO)20 Me (Cl2CHCO2)Reo (Cl2CHCO)20 One stereocenter(★ controls the induction n-c,Hos of six additional centers Ho C D n-C12H25 Meo niacin HO2C Monensin McDonald, F. E. Pure App. Chem., 1998, 70, 35
Me Me Et Me O Me Me Me HO H Et O Me O Me Me Et Me O Me HO2C Me OH Me OH H O LnM O Me Et Me Me HO OH O Me Me Me AcO H Et OH (Cl2CHCO2)ReO3 (Cl2CHCO)2O O Me Me AcO H Et O Me H H OH C D O O O O O Me MeO Me HO2C HO Me Me Me Me H Et H H H OH Me OH H C D HO O O Me O Et H H O H H O H H OH n-C12H25 n-C12H25 O H n-C12H25 OH Et O H H O H H O H H OH n-C12H25 HO O O Me n-C12H25 OH (Cl2CHCO2)ReO3 (Cl2CHCO)2O NHSO2CF3 NHSO2CF3 Application of the model for syn-oxidative polycyclization using an all (Z)-polyolefin: McDonald, F. E. Pure App. Chem., 1998, 70, 355. (Z,Z,Z)-premonensin triene Monensin C. A. Morales Olefin Addition Rxns in Polyether Synthesis-3 Chem 206 AD-mix b CrO3(py)2 1) Ac2O, Et3N cat. DMAP 2) NaBH4, CeCl3 5 Goniocin 5 (E,E,E)-pregoniocin triene Et2Zn, Ti(O-i-Pr)4 * * One stereocenter ( ) controls the induction of six additional centers. * Application of the model for syn-oxidative polycyclization on an all (E)-polyolefin:
