Enantioselective [3+2] Cycloadditions

Significance

A [3+2] cycloaddition between various enones 1 and α-allenic ester 2 yields cycloadducts of type 3a and 3b with excellent regioselectivity and high enantiomeric ratios. The authors apply nonproteinogenic, phosphine-containing α-amino acid derivative 4 as catalyst, which was previously used as ligand by the group of Grützmacher (Dalton Trans. 2006, 137). In addition, the use of chiral racemic β-substituted allenoate 5 with chalcones 6 as substrates represents a unique ‘deracemization’ reaction.