7,10-Anhydro Bafilomycin A1 - Synthesis and X-Ray Crystal Structure

Treatment of bafilomycin A1 with mercuric chloride resulted in a regioselective intramolecular oxymercuration. Reduction with triphenyltin hydride gave 7,10-anhydro bafilomycin A1 characterized by a single crystal X-ray analysis.     

Total synthesis of zincophorin and its methyl ester

A total synthesis of the naturally occurring ionophore zincophorin has been realized. The route features an intramolecular oxymercuration of a cyclopropanemethanol and a Carroll-Claisen rearrangement for the respective elaboration of the C1-C12 and C13-C25 subunits, which have been assembled by using a highly diastereoselective titanium-mediated aldol condensation.     

Development and applications of fluorogenic probes for mercury(II) based on vinyl ether oxymercuration

Mercury is a major threat to the environment and to human health. It is highly desirable to develop a user-friendly kit for on-site mercury detection. Such a method must be able to detect mercury below the threshold levels for drinking water, 1-2 ppb. We developed a fluorescence method based on the oxymercuration of vinyl ethers to detect mercury in dental and environmental samples. Chloride ions interfered with the oxymercuration reaction, but the addition of AgNO(3) solved this problem. Fine electronic and structural tuning led to the development of a more responsive probe that was less sensitive to chloride ion interference. This second-generation probe could detect 1 ppb mercury ions in water.     

The question of the reversibility in the aminomercuration of olefins. Synthesis of N-aryl-9-azabicyclo[4.2.1]and [3.3.1] nonanes by aminomercuration of cis-cis- 1.5-cyclooctadiene

The aminomercuration of olefins is found to be a reversible or irreversible process depending on the nature of the mercury(II) salt employed. This is in clear contrast with the mechanism of oxymercuration reactions. A selective synthesis of the title compounds is described by kinetically or thermodinamically controlled aminomercuration of cis-cis-1,5-cycloctadiene.     

Additions to bicyclic olefins—X: Stereochemistry of the oxymercuration-demercuration of cis-bicyclo[3.3.0]oct-2-ene,endo-trimethylene-norborn-8-ene and related olefins

The stereochemistry of the oxymercuration-demercurarion (OM-DM) of olefins related to the cis-bicyclo(3.3.0]octane and endo-2,3-trimethylenenorboniane structures was determined. In the case of cis-bicyclo(3.3.0]oct-2-ene, hydration occurs preferentially at the less hindered 3-position, with little preference shown for exo vs endo. The more hindered 2-product shows a 11:1 preference for the exo-product. The presence of Me groups at positions 2- or 3-, results in the formation of the tertiary alcohols with approximately a 4:1 favoring of the exo-isomer. (The oxymercuration intermediate exhibits a rapid equilibration with time. Consequently, the 4:1 ratios may not represent the true limit for the isomer distribution in the initial kinetic product.) Similarly, 2-methylenebicyclo[3.3.0]octane reveals an 8:1 preferential formation of the exo-alcohol. In the case of endo-trimethylene-norborn-8-ene, the oxymercuration stage is extraordinarily slow and the results do not fit this pattern. Possibly the very slow oxymercuration stage permits equilibration of the initial reaction product. On the other hand, the reaction is fast with 8-methylene-endo-trimethylenenorbornane and the product is 100% of the tertiary exo-alcohol. The same behavior is observed for 2-methylenenorbornane. Surprisingly, 2-methylene-endo-trimethy-lenenorbornane fails to undergo oxymercuration. Consequently, both endo-trimethylenenorborn-8-ene and 2-methylene-endo-trimethylenenorbornane exhibit an exceptional inertness toward oxymercuration, presumably related to the highly rigid U-shaped structure of the parent system.     

Double intramolecular oxymercuration: the first stereoselective synthesis of the C10-C34 fragment of asimitrin

The first stereoselective synthesis of the C10-C34 fragment of asimitrin, a nonclassical acetogenin, has been achieved. A key feature of our approach is the application of stereoselective double intramolecular oxymercuration for the efficient preparation of a mono-hydroxylated unsymmetrical bis-THF ring with two flanking hydroxyl groups. A chelation-controlled Grignard reaction plays a pivotal role in the elaboration of a commercially available carbohydrate.     

Stereo- and regioselective oxymercuration - demercuration of bicyclo[3.2.1]Oct-2-ene skeleton

The oxymercuration - demercuration of ethylene ketal of bicyclo-[3.2.1]oct-2-en-8-one is reported. This reaction proceeds with high regio- and stereoselectivity.     

Stereoselective synthesis of the macrolactone core of (+)-neopeltolide

A stereoselective synthesis of the macrolactone core of the potent anticancer agent neopeltolide is disclosed. The key steps of the synthesis include asymmetric allylation using Krische' protocol, conjugate reduction using MacMillan's methodology, and an asymmetric hetero-Diels-Alder reaction using Jacobsen's catalyst. Substrate controlled diastereoselective 1,3-anti reduction of a keto alcohol, Luche reduction followed by Ireland-Claisen rearrangement, oxymercuration, and reductive lithiation are other key steps.     

Highly efficient and diastereoselective synthesis of (+)-lineatin

[reaction: see text] A linear sequence was used to synthesize (+)-lineatin in 14 steps and 14% overall yield from a homochiral 2(5H)-furanone. Key steps of this synthetic approach feature the diastereoselective construction of a cyclobutene through a photochemical [2 + 2] cycloaddition and a regiocontrolled oxymercuration reaction.     

A new nucleophilic addition/ring-closure sequence. Enantioselective synthesis of 3-deoxy-8-oxatropanes

[reaction: see text] A study of new nucleophilic addition/ring-closure (NARC) sequences has resulted in the development of a stereoselective synthetic route to 3-deoxy-8-oxatropanes. The new sequences consisted of either a syn or anti aldol addition, employing an omega-alkenoyl sultam, followed by two-step bicyclic ring construction involving, consecutively, ring-closing metathesis and intramolecular oxymercuration.     

Hydroboration and Oxymercuration of Some 1-Substituted Norborn-2-enes

The 1-substituted norborn-2-enes 11–13 and 18 react with electrophiles under kinetic control preferentially in 2-position. The regioselectivity in oxymercuration is higher than in hydroboration and reaction with aqueous palladium chloride.     

Biyclo[2.2.1]heptane as cyclopentane precursor. Part 4 Stereocontrolled syhthesis of a potential intermediate to chromophycane dolastane and clavularane

The regio– and stereoselective synthesis of the keto-esters 20 and 22 are described, the latter being a potential intermediate to several diterpenes. The key steps involve the Diels-Alder cycloaddition between the benzocycloheptenone 5 and cyclopentadiene followed by a regioselective functionalisation of the adduct 6. A remarkable reversal of regioselectivity was observed during oxymercuration of the unsymmetric double bond in 6 and its reduced product 11 leading to 8 and 12 which were subsequently transformed to 20 and 22 respectively.     

Stereoselective demercuration of α-mercuriocarboxylates

Organomercurials, obtained by oxymercuration of α,β-dialkyl-α,β-unsaturated esters, undergo demercuration with a stoichiometric amount of sodium borohydride to give products arising predominantly (70–86%) from a net inversion of stereochemistry; conversely, demercuration with 1,3-propanedithiol occurs predominantly (80–95%) with net retention of stereochemistry.     

Cyclization of dienols, polyenes, and dienyne mediated by mercuric salts: course of cyclizations controlled by stability of cationic intermediates

Course of cyclization of dienols, polyenes, and dienyne mediated by mercuric salts were controlled by stability of cationic intermediates and source of mercuric salts. Reaction of (E)-5,9-dimethyl-4,8-decadiene-1-ol with mercuric acetate gave the intramolecular oxymercuration product, whereas one with mercuric triflate produced the olefin cyclization products.     

One-step synthesis of 4-aminodihydrobenzofurans and 4-hydroxyindoles via dehydrogenation-heteromercuration of 2-alyl-3-aminocyclohexenones using mercury(II) acetate

On treatment of the 2-allyl-3-aminocyclohexenones with mercury(II) acetate, either sequence, dehydrogenation—oxymercuration or dehydrogenation—aminomercuration, occurred depending on the nature of the amino group in the substrate to yield the dihydrobenzofurans or indoles, respectively.     

Yb(OTf)(3)-Catalyzed oxymercuration of homoallylic alcohol-derived hemiacetals and hemiketals

1,3-Diol synthons, protected as acetonides or benzylidene acetals, may be synthesized efficiently from homoallylic alcohols and acetone or benzaldehyde by oxymercuration of the derived hemiketals and hemiacetals with HgClOAc. The use of catalytic amounts of Yb(OTf)(3) is crucial to the success of the reaction, which was determined to be reversible.     

ω-Hydroxy and ω-Amino-carboxylic Acid Derivatives for the Preparation of Ester and Amide Crown Ethers

An oxymercuration reaction between methyl acrylate and the monobenzyl ethers (3) of mono-, di-, and triethylene glycol, followed by reduction with sodium borohydride, gives the expected polyether esters (4). These are converted by standard procedures into various derivatives of the ω-hydroxy and ω-amino acids (1) and (2) respectively.     

Hétérocyclisations intramoléculaires par réaction d'oxymercuration. I — synthèse et configurations des hétérocycles

We have accomplished the intramolecular oxymercuration of γ-δ ethylenic alcohols, with different mercuric salts under different conditions. By “in situ” reduction, or by direct reduction of isolated mercuric compounds, we obtain, in some cases, diastereoisomers with different relative yields.     

Expeditious total syntheses of natural allenic products via aromatic ring umpolung

Concise diastereoselective syntheses of the marine (+/-)-panacene and terrestrial (+/-)-desbromopanacene have been achieved in a few steps based on a concept of "aromatic ring umpolung". The synthetic avenue to the (+/-)-panacene involved a novel oxymercuration strategy to produce the correct configuration of the bromoallene moiety.     

Double intramolecular oxymercuration: stereoselective synthesis of highly substituted bis-tetrahydrofuran

Stereoselective intramolecular oxymercuration has been demonstrated as the key reaction for the efficient preparation of mono- and dihydroxylated unsymmetrical bis-tetrahydrofuran skeletons present in naturally occurring biologically active acetogenins using carbohydrates. These trans- and syn-selective intramolecular oxymercurations were explored in an enantioselective synthesis of the bis-tetrahydrofuran skeleton of mucoxin.