Cyclohexylidene enol carboxylates

Variation of the electronic and steric nature of the ruthenium catalysts allow the complementary carboxylative cyclization of 1,6-diynes (Scheme 36) [150]. Lee and coworkers described how a variety of carboxylic acids condense with 1,6-terminal diynes in the presence of catalytic amounts of [Ru(p-cymene)Cl2l2. P(4-F-C6H5)3 and 4-dimethylaminopyridine to give cyclohexylidene enol carboxylates with exclusive ( )-selectivity. The proposed mechanism involves the initial formation of a ruthenium vinylidene species I followed by intramolecular cyclization induced by the nucleophilic attack of the carboxylate anion to afford a vinylmthenium species II. Final protonolysis furnished the product and turns the catalyst over. 

Scheme 36 Ru-catalyzed carboxylative cyclization of 1,6-diynes to cyclohexylidene enol carboxylates...

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See also in sourсe #XX -- [ ]

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