Asymmetric synthesis of β-amino-γ-substituted-γ-butyrolactones: double diastereoselective conjugate addition of homochiral lithium amides to homochiral α,β-unsaturated esters

Abstract

Chiral α,β-unsaturated esters, containing a single, γ-stereogenic centre, show modest levels of substrate control upon conjugate addition of lithium dibenzylamide. Double diastereoselective conjugate additions of homochiral lithium N-benzyl-N-(α-methylbenzyl)amide to the homochiral α,β-unsaturated esters display “matching” and “mismatching” effects. In each case, however, these additions proceed under the dominant stereocontrol of the lithium amide to give the corresponding β-amino esters in high de. A remarkable reversal in stereoselectivity is noted by changing the ester functionality to an oxazolidinone. Subsequent O-deprotection and cyclisation of the resultant β-amino adducts gives access to the corresponding β-amino-γ-substituted-γ-butyrolactones in good yield and high de.