Diastereoselective addition achiral carbon nucleophiles

DIASTEREOSELECTIVE ADDITIONS OF ACHIRAL CARBON NUCLEOPHILES TO CHIRAL SUBSTRATES... 

DIASTEREOSELECTIVE ADDITIONS OF CHIRAL CARBON NUCLEOPHILES TO ACHIRAL SUBSTRATES... 

The chiral auxiliary mediated aza-Claisen rearrangement of /V-allylketcnc. V.O-acetals also allows the diastereoselective construction of quaternary carbon centers642. Butyllithium proved to be an unsuitable base for the neutralization step in this case because the increased steric hindrance at C-l causes C-2 nucleophilic addition to become competitive with C-l deprotonation. However, this problem can be overcome by the use of lithium tov-butoxide or lithium isopropoxide. This is shown for the achiral. V-allylketene A. O-aceta] precursor 8. 

Similarly, the two faces at a trigonal carbon in a molecule containing a chiral center are diastereotopic. Both chiral and achiral reactants can distinguish between these diastereotopic faces. Many examples of diastereoselective transformations of such compounds are known. One of the cases which has been examined closely is addition reactions at a trigonal center adjacent to a chiral carbon. Particular attention has been given to the case of nucleophilic addition to carbonyl centers. 

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