Methoxymercuration-demercuration

The technique of methoxymercuration-demercuration was utilized to determine the position of double bonds in the side chains. Since this method is not successful with the free alkaloids (272), the secondary amino groups must be protected as the A -heptafluorobutyramide. These amides are treated with mercuric acetate and methanol followed by reduction with sodium borohydride to yield the methoxylated compounds (273). The mass spectra of these compounds show a fragment ion (274) at m/z 59 indicating terminal double bonds in every case (Scheme 22) 16,25,410,411). 

D. R. (1980). Application of methoxymercuration-demercuration followed by mass spectrometry as a convenient microanalytical technique for double-bond location in insect-derived alkenes. J. Chem. Ecol., 6, 257-269. 

New 2,6-dialkylated piperidines (207-210) have been isolated as cis/trans mixtures from the ant venom of Monomorium delagoense [487], Their structures were determined using MS, catalytic hydrogenation to the hydrocarbons, and methoxymercuration-demercuration followed by MS analysis. The structures of 207-209 were confirmed by synthesis of the cis/trans mixtures from the corresponding dialkyl pyridines. The major venom component, cis/trans 207, displayed potent insecticial activity against Reticulitermes worker termites (LD50 = 150 pg/g termite). In addition, 207 was a potent repellent for the ants Pheidole and Iridomyrmex [487],... 

By an analogy to the radical syntheses above, the carbon chain elongation reaction was achieved by Barton et al. [109] in the reaction with ethyl a-trifluoroacetoxy acrylate 165. Under radical conditions 165 was coupled with the ester 164 prepared from pentaacetyl gluconic acid and /V-hydroxy-2-thiopiridone (Scheme 35) to afford an unstable intermediate 166, readily convertible to the unsaturated a,p-keto acid 167. The methoxymercuration-demercuration of 167 gave a low selectivity, providing the mixture of 3-deoxy-4-methoxy-D-man/jo and D-g/wco-octulosonic acids (4 3) in a moderate yield [110]. 

Catalytic hydrogenation of the olefmic linkage of the arabino isomer 181 led to 2-deoxy-DAH (182), whereas fully regioselective methoxymercuration-demercuration reaction, followed by phosphorylation of 7-OH group afforded DAHP derivative 187 (Scheme 39) [120b],... 

The lyxo isomer of 181 submitted to methoxymercuration-demercuration reaction provided the epimeric compound 188 with full regio- and stereoselectivity [120a]. Its transformation to the corresponding heptulosaric acid derivative 189 (Scheme 40) was easily accomplished applying KBr/TEMPO/NaOCl assisted oxidation. 

Steric effects may play a role in the regiochemistry of the reaction as well. While the oxymercuration-demercuration reaction is generally considered to give only Markovnikov hydration, as shown by predominant formation of 43, this regioselectivity is not absolute. For example, methoxymercuration of 3,3-dimethyl-l-butene produced 2% of 3,3-dimethylbutyl methyl ether (44, equation 9.42). ... 

The methoxymercuration of 4,6-0-benzylidene-D-allal yielded isomeric acetoxy-mercurial adducts having the -D-allo (439) and a-D-altro (440) configurations. Demercuration of (439) with sodium borohydride gave methyl 4,6-0-benzylidene-2-deoxy-P-D-ri6o-hexopyranoside (72%), the ot,p-unsaturated aldehyde (441) (8.3 %), and a trace of the original glycal, while demercuration of (440) gave methyl 4,6-0-benzylidene-2-deoxy-a-D-r/6o-hexopyranoside (40%), (442) (23.5%), and traces of other products. 

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