Lactone synthesis carbopalladation

Carbopalladation and ajkoxypalladation are the key steps in a new synthesis of the Corey lactone diol (10) in about 35% overall yield from cyclopentadiene. The... 

Ali and Alper later developed a method for y-lactone formation under neutral conditions from allylic alcohols according to Scheme 23, involving Pd(0) and dppb. The same protocol was also applied to synthesis of a,/3-butenolides from propargylic alcohols. Other bidentate or monodentate ligands give inferior results, and this correlates well with bite angle effects on the rate of the CO insertion reaction. Also, the allylic alcohol needs to be a-alkyl substituted to facilitate ring closure, in accordance with other studies.t t This process was postulated by the authors to be of the carbopalladative type. 

The synthesis of a-methylene- y-lactones from 3-butyn-l-ols, reported by Norton and co-workers is clearly a carbopalladative process, as demonstrated by careful mechanistic and kinetic studies. Nevertheless, from a synthetic standpoint, the process is closely related to the lactonization reactions that form the topic of this section, and for this reason it is briefly mentioned here. The catalyst system that was developed for this reaction comprises PdCySnCyPRs and was successfully applied to a number of different alkynols to prepare fused ring lactones (Scheme 27) in fair to excellent yields. 

---