Cascade carbopalladation oxygen nucleophiles

Since hydroxy groups do not interfere with palladium catalysts, the termination of carbopalladation cascades by oxygen nucleophiles has been employed in various cases. As... 

As hydroxy groups do not interfere with palladium catalysts, the termination of carbopalladation cascades by oxygen nucleophiles has been employed in various cases. As discussed earlier, the palladium-catalyzed couphngs of alkenyl halides with alkenes can give rise to the formation of it-allylpaUadium complexes, which can then be attacked by internal nucleophiles including hydroxy groups to yield various oxacychc systems (Scheme 8.38) [343]. 

Scheme 8.38 Intramolecular termination of carbopalladation cascades by oxygen nucleophiles [343].

Oxygen nucleophiles have not frequently been used as terminators in cascade car-bometallation reactions. The intramolecular carbopalladation starting with an iodo- or trifluoromethylsulfonyloxyalkenyl-substituted derivative in the presence of tetrabutylam-monium acetate led to a suitable precursor of the sesquiterpene (-)-A (i )-capneUene. In this case, desymmetrization of the prochiral precursor was achieved using (5)-BINAP as the ligand on the palladium catalyst (Scheme 32). ... 

There are hardly any examples for the use of sulfur nucleophiles in terminating cascade carbopalladation sequences, in contrast to oxygen and especially nitrogen nucleophiles. One reason for this might be found in the problems associated with the high degree of coordination of the palladium with the less oxidized sulfur nucleophiles such as thiols. However, arylsulfinates are excellent nucleophiles for cascade termination reactions, as has been shown by Grigg et al. (Scheme 34). ... 

Hong and Overman reported the intramolecular termination of cascade reactions by oxygen nucleophiles in their studies on a novel synthesis of morphine (Scheme Starting from an iodophenol derivative tethered with an iodophenol silyl ether, intramolecular carbopalladation provided a bicycUc Tr-allylpalladium intermediate, which in turn was attacked by the oxygen functionality (Scheme 37). 

---

See also in sourсe #XX -- [ , , , , ]

---