Side reactions alkene carbopalladation

A detailed investigation with 10 summarized in Table 2 indicates that premature esterification and cyclopropanation (Type HI C— Pd process in Scheme 2) can occur as dominant side reactions but that, under the optimized conditions (entry 7), both can be suppressed to insignificant levels (<3%). It is also important to note that, in marked contrast with the cyclic acylpalladation (Type n Ac—Pd) discussed in Sect. VI.4.1.1, monosubstituted alkenes that can readily participate in dehydropalladation (e.g., 11) cannot undergo the cyclic carbopalladation-carbonylative esterification tandem process (Type II C-Pd) since they merely undergo the cyclic Heck reaction (Type I C— Pd process in Scheme 14). The contrasting behavior mentioned above may be attributable to a chelation effect exerted by the carbonyl group in the acylpalladation (Scheme 15), which is lacking in the carbopalladation shown in Scheme 14. 

An analogous carbopalladation-cyclizaton process has been applied to the synthesis of various substituted tetrahydrofurans using three components. This one-pot procedure involves an intermolecnlar addition of allylic alkoxides to Michael acceptors. The resulting enolate nndergoes cyclization via nucleophilic attack on the alkene-Pd complex. So as to avoid nndesired side reactions snch as the premature trapping of the alkoxide by the organopalladinm species, the alkoxide shonld be added via a syringe pump. ... 

Side chain introduction by carbopalladation has been utilized in a total synthesis of an-thramycin methyl ether (32) (Scheme Heck reaction of the alkenyl triflate 30 with acrylamide installs the necessary three-carbon chain in moderate yield. The desired alkene geometry and oxidation state are observed in the dienamide 31 with no need for protection of the primary amide. The organopalladium precursor can also be part of the side chain being introduced as illustrated in a synthesis of prostaglandin E2 33. ... 

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