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1.7.7.8.2 Metal Removal To Generate an Ester

DOI: 10.1055/sos-SD-001-00654

Stephenson (Product Subclasses 17), G. R.; Perseghini, M.; Togni (Product Subclass 8), A.Science of Synthesis, (20011861.

A typical decomplexation procedure to detach the dicarbonyl(cyclopentadienyl)iron group is employed with a cycloaddition product,[‌883‌,‌1006‌,‌1007‌] and at the end of an iron-mediated route to hydroazulenes,[‌885‌‌887‌] to form methyl esters. Ammonium cerium(IV) nitrate is used in methanol in both cases. Oxidation with chlorine in methanol was used to form a methyl ester in a synthesis of ()-(S)-methyl tropinate.[‌985‌] Lactones can be made by an intramolecular version of this procedure, which induces cyclization to an alcohol substituent in the ligand.[‌1008‌] Strained-ring β-lactones are also formed in this way,[‌976‌] with bromine in dichloromethane used as the oxidant. When the dicarbonyl(cyclopentadienyl)iron group is a substituent on an α,β-unsaturated aldehyde, metal removal with lactone formation can be performed simply by addition of a Grignard or organolithium reagent, which effects CC bond formation at the aldehyde to generate an alkoxide that displaces the metal by attacking a carbonyl group. Metal and formyl substituents are placed on the same side of the alkene in this procedure.[‌1009‌] An intramolecular version of this procedure, but with zinc chloride used as the Lewis acid, produces a tricyclic ether (Scheme 113).[‌1010‌] This is a sequence of reactions (see Sections 1.7.7.3 and 1.7.7.4.4) that proceeds by the formation of a η1-complex from a η2-complex, and ends with oxidative decomplexation to generate the ester in the target 286.[‌1010‌]

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