Soft carbon nucleophiles termination

D.ii.a. Termination by Soft Carbon Nucleophiles. Termination by stabilized enolates as carbon nucleophiles has mostly been achieved using dialkyl malonate enolates, which in general cause no problans in connection with palladium catalysts and have a high enough nucleophihcity. 

The TT-allylpalladiLim complexes formed as intermediates in the reaction of 1,3-dienes are trapped by soft carbon nucleophiles such as malonate, cyanoacctate, and malononitrile[ 177-179). The reaction of (o-iodophenyl-methyl) malonate (261) with 1,4-cyclohexadiene is terminated by the capture of malonate via Pd migration to form 262. The intramolecular reaction of 263 generates Tr-allylpalladium, which is trapped by malononitrile to give 264. o-[odophenylmalonate (265) adds to 1,4-cyciohexadiene to form a Tr-allylpalladium intermediate via elimination of H—Pd—X and its readdition, which is trapped intramolecularly with malonate to form 266)176]. 

The allylic esters 189 and 191 conjugated with cyclopropane undergo regio-selective reactions without opening the cyclopropane ring. The soft carbon nucleophiles are introduced at the terminal carbon to give 190, and phenylation with phenylzinc chloride takes place on the cyclopropane ring to form 192[120]. 

Intennolecular termination processes by carbon nucleophiles will be considered separately for reactions with soft nucleophiles (i.e., mostly stabilized enolates) and with organometal-lic compounds such as stannanes, boranes, and zincates. 

Cp carbon atom of the ynamine at the electrophilic terminal pentatetraenylidene atom, followed by cycloreversion. These observations seem to indicate a marked preference of soft nucleophiles for the Ce carbon atom and hard nucleophiles for the central carbon of the unsaturated chain. 

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