Diastereospecific carbonylation of π-allylpalladium complexes to give 3,6-disubstituted 3,6-dihydro-1H-pyridin-2-ones

Abstract (Ph 3 P) 2 PdCl 2 was found to be the most effective of a range of catalysts for decarboxylative carbonylation of (4 S ,5 RS )-5-ethenyl-4-(2-propyl)oxazolidin-2-one to give the δ-lactam, (6 S )-3,6-dihydro-6-(2-propyl)-1 H -pyridin-2-one. In a similar way, diastereoisomerically pure (4 S ,5 S )-4-benzyl-5-(( Z )alk-1-enyl)oxazolidin-2-ones undergo stereospecific carbonylation to give (3 R ,6 S )-6-benzyl-3-alkyl-3,6-dihydro-1 H -pyridin-2-ones. The diastereoisomeric (4 S ,5 R )-4-benzyl-5-(( Z )alk-1-enyl)oxazolidin-2-ones give rise to a separable mixture of the corresponding (3 S ,6 S )-6-benzyl-3-alkyl-3,6-dihydro-1 H -pyridin-2-one and (4 S ,5 S )-4-benzyl-5-(( E )alk-1-enyl)oxazolidin-2-one. Under more forcing conditions, the latter oxazolidinone is carbonylated to the 3,6- anti -pyridinone. The stereochemical course of the reactions can be rationalized by formation of a π-allyl palladium cation with inversion of configuration followed by carbonylation with retention. The stereospecificity observed in our system precludes metal–metal exchange of the π-allyl complexes by a Pd(0) displacement process.