5 Addition to R S M L Nu d.e.% H Me Et Ph MeMgI EtMgBr PhMgBr EtMgI PhMgI334350>60667583Cram & Elhafez, J Amer Chem Soc 1952, 74, 5828.
6 Faulty Assumptions Ground state and reactive conformation are wrong. Ground state and reactive conformation (TS) cannot be assumed to be the same.The directing influence of substituents does not only derive from their steric effects. Electronic interactions are crucial.The C=O group assumes pyramidal state early, therefore Cram model is unfavourable.
15 Auxiliary attached to nucleophile J C S Perkin I 1981, 1278
16 Organometallic: Chiral ligand Tetrah Lett 1986, 27, 5711
17 Allylic nucleophiles Alternative route to aldol-type products Two new chiral centres introducedComplication: reaction at C-1Achiral reactants: syn and anti racematesChiral reactants: in principle one major stereoisomer
27 Addition to aldehydes R e.e. % Yield % Me 93 74 Et 86 71 iPr 90 86 nButBuPh
28 Other allylic boranes High diastereoselectivity and enantioselectivity Reagent enantioselectivity overrides intrinsic chiral aldehyde facial selectivityConsistent and predictableAlso with -chiral aldehydesDiamine-based ligands
29 Allylsilanes and Allylstannanes Promoted by Lewis acidsHigh diastereoselectivity‘Cram controlled’“Chelation controlled’
31 Chiral ligand as catalyst Organometallic reagent must be relatively unreactive towards C=O unless combined with the catalyst – ligand acceleration.Catalyst must have suitable 3D structure to provide high e.e.
32 Dialkylzinc addition to aldehydes R Nu e.e., %Ph MePh EtPh Bup-Cl-Ph Etp-MeO-Ph Et2-Furyl C5H >95(E)-C6H5-CH=CH Et(E)-Bu3SnCH=CH C5HPhCH2CH2 EtJ Amer Chem Soc 1986, 108, 6071