Intramolecular reactions neutral manifold

The most common Mizoroki-Heck reaction mechanism is called the neutral mechanism, because its intermediates are uncharged. The catalytic cycle for the neutral manifold of the intramolecular Mizoroki-Heck reaction of alkenyl and aryl halides is shown in Scheme... 

Asymmetric intramolecular carbopalladation is an effective reaction for producing enantioenriched polycycles. Most examples are intramolecular Heck reactions. One seminal example from natural product synthesis is the 5-exo carbopalladation of eneamide 201 to oxindole 202 (after acid treatment) from a total synthesis of ( )-physostigmine 203 (Scheme 31).The reaction occurs in 84% yield with 95% ee, which is remarkably efficient for the construction of a quaternary center. Reaction conditions that favor the neutral manifold of the Heck reaction are employed. Examination of the scope of the oxindole synthesis and mechanistic analysis have appeared. " Group selective reactions are also powerful reactions in carbopalladation asymmetric synthesis.From a synthesis of (+)-vemolepin 206, alkenyl triflate 204 is... 

As in the uncatalyzed reactions with enamines (vide supra), there is potentially more than one point where stereochemical differentiation can occur (Scheme 59). Selectivity can occur if the initial addition of the enol ether to the Lewis acid complex of the a,/J-unsaturated acceptor (step A) is the product-determining step. Reversion of the initial adduct 59.1 to the neutral starting acceptor and the silyl enol ether is possible, at least in some cases. If the Michael-retro-Michael manifold is rapid, then selectivity in the product generation would be determined by the relative rates of the decomposition of the diastereomers of the dipolar intermediate (59.1). For example, preferential loss of the silyl cation (or rm-butyl cation for tert-butyl esters step B) from one of the isomers could lead to selectivity in product construction. Alternatively, intramolecular transfer of the silyl cation from the donor to the acceptor (step D) could be preferred for one of the diastereomeric intermediates. If the Michael-retro-Michael addition pathway is rapid and an alternative mechanism (silyl transfer) is product-determining, then the stereochemistry of the adducts formed should show little dependence on the configuration of the starting materials employed, as is observed. 

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