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Mark Lautens

Publications and source records attributed to Mark Lautens.

At least 55 records · Page 3Linked to original sources
PubMed2003

Synthesis of novel tetracycles via an intramolecular Heck reaction with anti-hydride elimination.

[reaction: see text] The catalytic combination of Pd(2)(dba)(3)/HP(t-Bu)(3).BF(4) and DABCO gives an unusual intramolecular Heck reaction with dihydronaphthalene substrates, yielding formal anti-hydride elimination products in good to excellent yields under mild conditions. For dibromo substrates, multiple Heck reactions are possible when an external acceptor is added to afford more highly functionalized products.

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PubMed2003

Palladium(II) catalyst systems for the addition of boronic acids to bicyclic alkenes: new scope and reactivity.

[reaction: see text] The palladium-catalyzed ring-opening addition of arylboronic acids to heterobicyclic alkenes is reported. Excellent yields are obtained for the addition of a wide variety of arylboronic acids to aza- and oxabicyclic alkenes. This methodology is especially useful in the synthesis of 1-amino-2-aryldihydronaphthalene scaffolds, for which rhodium catalysts are currently unreactive or give complex mixtures. Asymmetric versions of these reactions are under development, and preliminary results are reported.

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PubMed2003

Diastereoselective palladium-catalyzed formate reduction of allylic carbonates as a new entry into propionate units.

[reaction: see text] The diastereoselective palladium-catalyzed formate reduction of allylic carbonates is described. Reduction of allylic carbonates under mild conditions (Pd(OAc)(2) (2.5-5 mol %), [n-Bu(3)PH]BF(4) (2.5-5 mol %), HCO(2)H/Et(3)N (1:2) (3 equiv), CH(3)CN (0.05M), 40 degrees C) affords the terminal olefin as the syn isomer in good yields and modest to excellent diastereoselectivity. These compounds, which are useful building blocks for the synthesis of polypropionate units, are the synthetic equivalent of the products obtained from an aldol reaction of an alpha-methyl-beta,gamma-unsaturated aldehyde.

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PubMed2003

Mild procedure for the catalytic bis(stannylation) of alkynes with hexaalkylditins.

[reaction: see text] Bis(stannylation) of terminal alkynes is achieved through the use of a palladium-isonitrile catalyst complex using a hexaalkylditin as a stannyl group transfer reagent in an atom-efficient and mild catalytic process. Functional group tolerance is good, allowing the presence of amine, carbamate, silyl, ester, and ether moieties. An activated internal alkyne also underwent bis(stannylation) in moderate yield, allowing access to symmetrical bis(alkenyl)stannanes.

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PubMed2003

MgI(2)-mediated ring expansions of secondary methylenecyclopropyl amides.

Ring expansion of secondary methylenecyclopropyl amides in the presence of MgI2 was investigated. Various isomeric five-membered unsaturated lactams were obtained, depending on the character of the substituent Q. The amide group served as a nucleophile in ring closing as well as an activator for ring opening. In the presence of a variety of aryl aldimines or aldehydes, alkylative ring expansion occurred in a single step under mild and neutral conditions leading to gamma'-amino- or -hydroxy-alkylated pyrrol-2-ones. Also, it was shown that a 4-methylpyrrol-2-one could be transformed to a gamma-hydroxy-alkylated product by the use of a direct vinylogous aldol reaction.

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PubMed2003

Rhodium-catalyzed addition of arylboronic acids to alkynyl aza-heteroaromatic compounds in water.

Alkynyl heteroaromatic compounds reacted with arylboronic acids to give addition products in the presence of a rhodium catalyst. The best results were obtained when a novel pyridine-substituted water-soluble phosphine ligand was used. The reactions proceed to give trisubstituted alkenes from various arylboronic acids and alkynyl heteroaromatic compounds with high regioselectivity. Only alkynes with a nitrogen atom in proximity to the triple bond were converted to the corresponding alkenes, as expected for a chelation-controlled addition.

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PubMed2003

Transition metal-catalyzed enantioselective ring-opening reactions of oxabicyclic alkenes.

Over the past five years, several metal-catalyzed asymmetric ring-cleaving reactions have been developed that generate ring-opened products in high yield and enantiomeric excess. These reactions can be carried out with a range of nucleophiles including hydride, stabilized and nonstabilized carbanions, alcohols, amines, and carboxylates. To achieve these results, three different transition metals have been employed, namely nickel, palladium, and rhodium, leading not only to synthetically useful transformations but also to a greater understanding of the reaction manifolds possible with these metals. This Account covers the work by our group and by others toward the development of new metal-catalyzed asymmetric ring-opening reactions of oxabicyclic alkenes.

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PubMed2002

Remote electronic effects in the rhodium-catalyzed nucleophilic ring opening of oxabenzonorbornadienes.

We report the application of our rhodium-catalyzed nucleophilic ring-opening methodology to unsymmetrically arene-substituted oxabenzonorbornadienes. The regioselectivity of the ring opening was investigated using a variety of nucleophiles that led to a broad selection of dihydronaphthalene products. It was found that good to excellent regioselectivities are obtained using strongly pi-donating substituents, whereas sigma-donating and electron-withdrawing functionalities have a minimal effect. Post ring-opening manipulations of functional groups in the dihydronaphthalene products were shown to give efficient access to mono- and diamine tetrahydronaphthalene building blocks.

Bridged Bicyclo Compounds, Heterocyclic↗
PubMed2002

An expedient enantioselective route to diaminotetralins: application in the preparation of analgesic compounds.

Advances to the rhodium-catalyzed asymmetric ring-opening protocol have allowed this methodology to be extended to azabicyclic alkenes, the first time that rhodium has been used in allylic functionalizations with nitrogen leaving groups. The product diaminotetralins are important medicinal compounds. The synthetic utility of this methodology has been demonstrated in the total synthesis of an analgesic compound where the tetralin core, the regiochemistry, and the relative and absolute stereochemistry are all established in the ring-opening step. [reaction: see text]

Analgesics↗
PubMed2002

Diastereoselective formation of indanes from arylboronate esters catalyzed by rhodium(I) in aqueous media.

[reaction: see text] Arylboronate esters bearing a pendant Michael-acceptor alkene can add to norbornene and cyclize to give indane systems in yields ranging from 62% to 95% with high diastereomeric excess (>20:1). The reaction is performed in an organic/aqueous emulsion and catalyzed using [Rh(COD)Cl]2 with t-Bu-amphos chloride, a sterically bulky, electron-rich, water-soluble phosphine ligand.

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PubMed2002

Divergent selectivity in MgI(2)-mediated ring expansions of methylenecyclopropyl amides and imides.

We report a novel approach to prepare five- and six-membered heterocyclic compounds via a ring expansion of monoactivated methylenecyclopropanes (MCPs) with aldimines and aldehydes in the presence of MgI(2). Monoactivated MCPs behave as homo-Michael acceptors to afford bifunctional vinylogous enolates in the presence of MgI(2). The carbonyl moiety of the monoactivated MCP dramatically influences the reaction site in the dienolate with aryl aldimines and aldehydes as well as the size of the ring. Excellent divergent selectivity to five- vs. six-membered heterocycles is observed: alpha-alkylation/5-exo-tet cyclization (Z = NPh(2)) vs. gamma-alkylation/6-exo-trig cyclization (Z = 2-oxazolidone). Analogously, the reaction of the MCP imide with alkyl aldimines demonstrates the same selectivity by varying the size of electrophile or the reaction temperature. In addition, we observe the first example of the formation of the gamma-alkylation adduct in the reaction of a vinylogous imide enolate with a carbonyl compound.

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PubMed2002

Palladium-catalyzed sequential alkylation-alkenylation reactions. Application to the synthesis of 2-substituted-4-benzoxepines and 2,5-disubstituted-4-benzoxepines.

The synthesis of 2-substituted-4-benzoxepines and 2,5-disubstituted-4-benzoxepines from aryl iodides and bromoenoates is described. This methodology is based on a palladium-catalyzed aromatic substitution followed by an intramolecular Heck sequence. Under the reaction conditions (Pd(OAc)(2) (10 mol %), tri-2-furylphosphine (20 mol %), norbornene (2 equiv), Cs(2)CO(3) (2 equiv), CH(3)CN, 85 degrees C), moderate to excellent yields of benzoxepines bearing numerous substituents (Me, F, Cl, etc.) are obtained.

Journal Article↗
PubMed2002

Total synthesis of ionomycin using ring-opening strategies.

[structure: see text] The total synthesis of the polyether antibiotic ionomycin, a calcium ionophore, is described. The synthesis demonstrates the utility of ring-opening methodologies as applied to the synthesis of polypropionate and deoxypolypropionate subunits, which are found in two of the four fragments in the synthesis.

Aldehydes↗
PubMed2002

Enantioselective allylation of beta,gamma-unsaturated aldehydes generated via Lewis acid induced rearrangement of 2-vinyloxiranes.

[reaction: see text] 2-Vinyloxiranes have been found to be excellent surrogates to beta,gamma-unsaturated aldehydes. These valuable electrophiles, generated in situ by treatment of a 2-vinyloxirane with a catalytic amount of Sc(OTf)(3), are effectively trapped by the chiral allylating agents based on alpha-pinene, affording bishomoallylic alcohols in high yield and excellent selectivity.

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PubMed2002

Halide effects in transition metal catalysis.

Among the most common ligands found on transition metal catalysts are halide ions. Of the commercially available catalysts or pre-catalysts, most are halo-metal complexes. In recent years, manipulation of this metal-halide functionality has revealed that this can be used as a highly valuable method of tuning the reactivity of the complex. Variation of the halide ligand will usually not alter the nature of the system to the extent that it becomes unreactive but will impart sufficiently large changes that differences in reactivity or selectivity occur. These differences are a product of the steric and electronic properties of the halide ligand which has the ability to donate electron density to the metal occurs in a predictable manner. Despite the common perception in asymmetric catalysis that halide ligands are of secondary importance compared to chiral ligands, halide ligands have been found to exert dramatic effects on the enantioselectivity of asymmetric transformations. While the mechanism of action is known for relatively few of the cases, many intriguing and potentially synthetically useful trends are apparent. This review discusses the physical properties of the halides and their effects on stoichiometric and catalytic transition metal processes. The metal-halide moiety thus emerges as a tunable functionality on the transition metal catalyst that can be used in the development of new catalytic systems.

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