D. A. Evans The Aldol Reaction: Anti Aldol Rxns of Chiral Ethyl Ketones Chem 206 Examples or:∑ others General Reaction R-CHO.R TBS ( Chx)2BCI TBSQ Syn Aldols syn-anti diastereomer General Reaction R-CHO TBS O CI TBSo 0 OH Anti Aldols 964(75%) Me MeMeMe Me The Transition States However, the preceding precedent does not extend to these systems RCHO 00 PrCHO Me me diastereoselection 84: 16 D.A. Evans, H. P Ng, J.S. Clark, D. L. Rieger Tetrahedron, 1992, 48, 2127-2142. disfavored An analogous case o OH Evans,JAcs1991,113,1047 (Chx)2BCl Bno Bno r Bno RCHO (E)Enolate Facial Bias MeMe Me Me Meme RCHO RIS diastereoselection 95: 5 disfavored I Patterson, J M. Goodman. M. Isaka Tetrahedron Lett. 1989. 30. 7121-7124 anti-anti diastereomer RCHO favored syn-anti diastereomer These enolates do not comply with steric analysis: electronic effects? Tetrahedron,1992,48,2127-2142H RL RM C H R Me H O O M L L O M O C H H Me R RL RM H L L ‡ ‡ O M RL RM Me O RM Me RL M O M RL RM Me R-CHO R-CHO O RM R L R OH Me Me OH R R L RM O O OH RM Me R RL Me Me O Me TBSO Me Me Me O Me TBSO Me O N Me O O O Me Bn RL R RM Me O O OH RM Me RL M C C C H RL Me Me O H M OH R RL O Me Me Me Me O RL R OH RL O Me Me BnO O Me Me Bn Me O O O Me O N RCHO RCHO RCHO BnO O Me Me R OH Me Me O BnO Me Me O Me TBSO Me Me OH Me Me Me O Me TBSO Me Me OH Me Xq R O O Me Me OH BnO O Me Me R OH Xq R O O Me OH Me D. A. Evans The Aldol Reaction: Anti Aldol Rxns of Chiral Ethyl Ketones Chem 206 General Reaction for Syn Aldols: Examples: 96:4 (75%) 94:6 (90%) Diastereoselection major : S others (Chx)2BCl Et3N iPrCHO iPrCHO (Chx)2BCl Et3N General Reaction for Anti Aldols: Evans, JACS 1991, 113, 1047. RCHO disfavored favored RCHO The Transition States: syn-anti diastereomer anti-anti diastereomer favored ? (E) Enolate Facial Bias disfavored ? syn-anti diastereomer D. A. Evans, H. P. Ng, J. S. Clark, D. L. Rieger Tetrahedron, 1992, 48, 2127-2142. (Chx)2BCl Et3N iPrCHO diastereoselection 84:16 However, the preceding precedent does not extend to these systems: I. Patterson, J. M. Goodman, M. Isaka Tetrahedron Lett. 1989, 30, 7121-7124. (Chx)2BCl Et3N diastereoselection 95:5 An analogous case: These enolates do not comply with steric analysis: ® electronic effects? Tetrahedron, 1992, 48, 2127-2142