Lactones, by carbonylation

Y-lMCtones Annulation of o-allyl aryl ketones to provide fused lactones by carbonylation under CO is observed in the presence of Cp2Ti(CO>2. 

Scheme 2.11 Bicyclic lactones by carbonylation of C-Hg bonds terminated by OH [23].

A catalytic asymmetric synthesis of a-methylene lactones by carbonylation of a meso substrate (Scheme 10) was developed by Shibasaki and co-workersJ The combination of Pd(OAc)2, (1 )-BINAP, and Ag20 gave 44% yield of lactone with a modest ee. No asymmetric induction occurred in the absence of Ag20. Presumably the role of Ag20 is to promote formation of an intermediate cationic palladium species, which could retain bidet tate coordination of the chiral ligand throughout the catalytic process. 

---