D. A. Evans Carbonyl Addition Reactions:(4)-Enolate Nucleophiles Chem 206 (Z) Enolates Exhibit Anti-Felkin Aldehyde Diastereoface Selection O OTBS Disfavored R Felkin anti-Felkin(Cram-Chelate) Me h OLi Felkin:anti-Felkin Me D W. Brooks Co-workers TMSO Me27:73 Tetrahedron Lett. 1982, 23, 4991-4994 Me me 9BBN Anti-Felkin The illustrated syn-pentane interaction disfavors the Felkin pathway I The bulky oTBS group disfavors chelation. (see Keck, JACS 1986, 108, 3847) Evans, Nelson, Taber, Topics in Stereochemistry 1982, 13, 1-115 I The boron and lithium enolates display nearly equal levels of anti-Felkin selectivity WR.Rush,og.chem.1991,56,4151-4157 An Early study rationalized results through chelated transition states Titanium enolates exhibit the same trend CH2OBn o H OCH2OBn OPMB OCH2OBn Felkin Anti-Felkin( Cram Chelate) anti-Felkin: Felkin 77: 23(78% 0 H OPMB OPMB Felkin: Anti-Felkin OCH,OBn 17:83 anti-Felkin: Felkin 56: 44(84%) 10:90 am1:87 Evans etal. JACS 1995. 117. 9073 Masamune Acs1982104,5526O iPr Me OH iPr Me OPMB Me iPr O TiCln O iPr Me OH iPr Me OPMB Me iPr O TiCln R Me O MLn H RL O Me Li O R Me OCH2OBn Me O H R" H Et O Me OCH2OBn OCH2OBn Me O H CHMe2 C6H11 Et Et C6H11 (R) C H O LnM O H Me Me H R L R R C H R L H H Me Me O MLn O Me O OCH2OBn Me OH R R" R R" OH Me O OCH2OBn Me R L O Me OH Me R R Me OH Me O R L H R" O Me O Li CH2OBn H O Me OTBS Me R Me OM OPMB Me O H iPr OPMB Me O H iPr O Me OH Me R Me OTBS TMSO Me OLi Me Me O 9BBN Me PhS Me OH Me O R Me OTBS Favored Disfavored Anti-Felkin + + ++ Felkin (Z) Enolates Exhibit Anti-Felkin Aldehyde Diastereoface Selection The illustrated syn-pentane interaction disfavors the Felkin pathway. Evans, Nelson, Taber, Topics in Stereochemistry 1982, 13, 1-115. W. R. Roush, J. Org. Chem. 1991, 56, 4151-4157. D. W. Brooks & Co-workers Tetrahedron Lett. 1982, 23, 4991-4994. Felkin anti-Felkin (Cram-Chelate) Felkin : anti-Felkin 27 : 73 29 : 71 ■ The bulky OTBS group disfavors chelation. (see Keck, JACS 1986, 108, 3847.) ■ The boron and lithium enolates display nearly equal levels of anti-Felkin selectivity. Titanium enolates exhibit the same trend D. A. Evans Carbonyl Addition Reactions: (Z)-Enolate Nucleophiles Chem 206 Si-face An Early study rationalized results through chelated transition states: Masamune JACS 1982, 104, 5526 Nu: Anti-Felkin (Cram Chelate) 13 : 87 8 : 92 10 : 90 17 : 83 (R") Felkin : Anti-Felkin Felkin anti-Felkin : Felkin 77 : 23 (78%) Evans etal. JACS 1995, 117, 9073 anti-Felkin : Felkin 56 : 44 (84%)