Organomercury couplings

The Pd-mediated coupling involving organomercury and alkenes is useful for the synthesis of C-5 substituted 2 -deoxyribonucleosides[376]. The ethylur-idine 415 is prepared by the reaction of the 5-chloromercuriuridine 414 with... 

Cacchi and Palmier (83T3373) investigated a new entry into the quinoline skeleton by palladium-catalyzed Michael-type reactions. They found that phenyl mercurial 134 was a useful intermediate for the synthesis of quinoline derivatives, and that by selecting the reaction conditions the oxidation level of the heterocyclic ring in the quinoline skeleton can be varied. On such example is shown in Scheme 16. PdCla-catalyzed coupling between organomercurial reagent 134 and enone 135 delivered adduct 136 which was subsequently cyclized to quinoline 137 under acidic conditions. 

Organomercuric compounds require nucleophilic assistance by soft iodide anions (cf. Section 9.6.3.2.2) for participation in cross-coupling reactions.158 The reaction is useful for aryl-aryl cross-coupling in those cases in which the organomercury species are obtained by direct mercuration of aromatic compounds (38).159... 

Homo-coupling of vinylic mercurials occurs readily under palladium195 or rhodium196 catalysis, but with the stoichoimetric amount of a reagent (equation 111)195. Divinylpal-ladium intermediates may be involved in this reaction. This reaction is also of limited synthetic scope since organomercurials are usually prepared via vinylboranes, which... 

Cyclization by amidomercuration has been reported (391). Reaction of N-methoxycarbonyl-6-aminohept-l-ene (211) with mercuric acetate gave the organomercurial (212). Reductive coupling of 212 with l-decen-3-one in the usual way gave the cis and trans isomers (213). Successive treatment of 213 with ethanedithiol, Raney nickel, and ethanolic hydrogen chloride afforded ( )-sole-nopsin A (Id, 2 parts) and its isomer (Ic, 3 parts), which were separable by preparative gas chromatography (GC) (Scheme 5) (391). 

Intramolecular Heck reaction of organomercurial 332 has been used to prepare unsaturated lactone 333 by a non-traditional strategy452. Sequential, regiospecific C—C and C—N bond-forming reactions via a novel Heck-type coupling have been developed453. 

Figure 4.5 Separation of two trialkyl lead and three organomercury species. Column 1.5mm i.d. x 5cm long flow rate lOOpimirT1 mobile phase 5mM ammonium pentanesulfonate in 20 80 v/v ACN-H20 (pH 3.4) injection volume 2jul, sample size, 40 pg (as Pb) for (Me)3Pb+, 80 pg (as Pb) for (Et)3Pb+ and 2 ng (as Hg) for each of the organomercury species. Taken from Speciation of mercury and lead compounds by microbore column liquid chromatography inductively coupled plasma chromatography mass spectrometry (Shum ef a/. 1992).

Krull, I.S., Bushee, D.S., Schleicher, R.G. and Smith, S.B. (1985) Determination of inorganic and organomercury compounds by high performance liquid chromatography-inductive ly coupled plasma emission spectrometry with cold vapour generation. Analyst, 111, 345-349. 

Moens, L., DeSmaele, T., Dams, R., VandenBroeck, R and Sandra, P. (1997) Sensitive, simultaneous determination of organomercury, -lead, and -tin compounds with headspace solid phase microextraction capillary gas chromatography combined with inductively coupled plasma mass spectrometry. Anal. Chem., 69, 1604—1611. 

The interface to couple HPLC columns with the atomizer can be very simple, with a direct connection from the exit of the column to the nebulizer of the AAS or plasma detector. Unfortunately, the efficiency of the nebulizer is very low (1-3%), which limits the sensitivity. A general way to circumvent this lack of sensitivity is postcolumn derivatization to form cold Hg vapor. However, the generation of a cold vapor from organomercury species requires an extra step their conversion to... 

De Smaele, T., L. Moens, R. Dams, R Sandra, J. Van de Eycken, and J. Vandyck. 1998. Sodium tetra( -propyl)borate A novel aqueous in situ derivatization reagent for the simultaneous determination of organomercury, lead- and tin-compounds with capillary gas chromatography-inductively coupled plasma mass spectrometry. J. Chromatogr. A 793 99-106. 

Over 35 years ago, Richard F. Heck found that olefins can insert into the metal-carbon bond of arylpalladium species generated from organomercury compounds [1], The carbopalladation of olefins, stoichiometric at first, was made catalytic by Tsutomu Mizoroki, who coupled aryl iodides with ethylene under high pressure, in the presence of palladium chloride and sodium carbonate to neutralize the hydroiodic acid formed (Scheme 1) [2], Shortly thereafter, Heck disclosed a more general and practical procedure for this transformation, using palladium acetate as the catalyst and tri-w-butyl amine as the base [3], After investigations on stoichiometric reactions by Fitton et al. [4], it was also Heck who introduced palladium phosphine complexes as catalysts, enabling the decisive extension of the ole-fination reaction to inexpensive aryl bromides [5],... 

J. Leenaers, W. van Mol, H. G. Infante, F. C. Adams, Gas chromatography-inductively coupled plasma-time-of-flight mass spectrometry as a tool for speciation analysis of organomercury compounds in environmental and biological samples, J. Anal. Atom. Spectrom., 17 (2002), 1492-1497. 

The mechanisms of reaction of organomercury compounds have been extensively investigated, but only a couple of basic points can be covered here. Reactions of the types shown below proceed via cyclic intermediates (or transition states), as shown. 

Cross-coupling of organomercurials has been employed the generation of solnble, well-characterized poly(3-alkylthiophene) and poly(3-alkylthienyl ketone). Facile mercuration of 3-alkylthiophenes with HgCl2 prodnces 2,5-bis(chloromercurio)-3-alkylthiophenes. The mercurated intermediates snbseqnently undergo cross-conpling reactions in the presence of Cn and PdCh to yield poly(3-alkylthiophene) and, under CO pressure, poly(3-alkylthienyl ketone) (Scheme 4). 

The organomercury compounds formed in such reactions are not of great synthetic importance, although they do undergo nitrosation reactions with nitrosyl chloride, NOCl. They can also be used as the organometallic component in certain palladium-mediated coupling processes. 

It had been known from the work of Heck and Tsuji that certain organopalla-dium(II) species convert olefins into vinylic C-C-coupling products, with the active species being generated in situ from organomercurials and common palladium(II) salts [10]. The need for stoichiometric reagents, however, did not attract much interest from organic chemists. It was only the discovery that direct oxidative addi-... 

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