Organomanganese (II) reagents XII: An efficient one-pot preparation of unsymmetrical secondary or tertiary alcohols

Various unsymmetrical secondary or tertiary alcohols have been prepared in high yields by an efficient one-pot procedure involving the acylation of an organomanganese reagent by an acyl chloride and addition to the ketone formed of various organometallic compounds (RLi, RmgX, LiAlH₄, NaBH₄. The complexation of the intermediate ketone by the metallic salts present in the reaction mixture allows to perform the 1–2 addition step under exceptionally mild conditions (0 to 20°C).     

Solvent-controlled diastereoselective synthesis of cyclopentane derivatives by a [3 + 2] cyclization reaction of alpha,beta-disubstituted (alkenyl)(methoxy)carbene complexes with methyl ketone lithium enolates

Reaction of alpha,beta-unsaturated methoxycarbene complexes 1 and 11 with methyl ketone lithium enolates 2 leads to the corresponding five-membered carbocyclic compounds 4 or diast-4 and 12. The influence of the solvent and/or cosolvent (PMDTA), which turned out to be crucial to direct the reaction to 4 or diast-4, is studied, and a tentative mechanism according to these facts is proposed. In addition, the reaction of carbene complex 1a with alkynyl methyl ketone lithium enolates can be directed to the formal [3 + 2] or [4 + 1] cyclization products by a slight variation of the reaction conditions. Finally, consecutive three-component coupling reactions with carbene complex 1a, lithium enolates 2, and aldehydes 18 to give, in a diastereoselective way, hydroxy carbonyl compounds 19 and tricyclic polyethers 20 are presented.     

Assembly of Fluorinated Quaternary Stereogenic Centers through Catalytic Enantioselective Detrifluoroacetylative Aldol Reactions

A Cu‐catalyzed asymmetric detrifluoroacetylative aldol addition reaction of 2‐fluoro‐1,3‐diketones/hydrates to aldehydes in the presence of base and chiral bidentate ligand was developed. The reaction was carried out under convenient conditions and tolerated a wide range of substrates, resulting in fluorinated quaternary stereogenic α‐fluoro‐β‐hydroxy ketone products with good chemical yields, diastereo‐ and enantioselectivities. This catalytic asymmetric detrifluoroacetylative aldol addition reaction provides a new approach for the preparation of biologically relevant products containing C? F quaternary stereogenic centers.     

Stereoselective aldol coupling of α,β-acetylenic ketones promoted by MgI2

A highly stereoselective synthesis of (Z)-β-iodovinyl ketone has been achieved with the tandem formation of CC and CI bonds in a three-component reaction. This new catalysis utilizes MgI₂ as a Lewis acid as well as an iodine source for a Michael-type addition. α,β-Acetylenic ketone is initially converted to an active β-iodo allenolate intermediate and then can be attacked by a variety of aldehydes to afford Z-selective Baylis-Hillman adducts in excellent yields.     

Synthesis of isoxazolidine derivatives from N-substituted hydroxylamines and α,Β-unsaturated ketones

The reaction of methyl vinyl ketone with N-Phenyl-hydroxylamine leads to a tautomeric mixture of 5-hydroxy-2-phenyl-5-methylisoxazolidine and its linear form, while the reaction with benzohydroxamic acid leads to linear products of addition to the oxygen or nitrogen atoms, depending on the reaction conditions. The first representatives of 5-hydroxyisoxazolidines with the residue of an aliphatic carboxylic acid attached to the nitrogen atom were obtained by acylation of 5-hydroxy-3,3,5-trimethylisoxazolidine.Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 6, pp. 823–826, June, 1989.     

Multicomponent, solvent-free synthesis of β-aryl-β-mercapto ketones using zirconium chloride as a catalyst

Zirconium chloride efficiently catalyzes the one-pot, three-component reaction of an aryl aldehyde, cyclic or acyclic enolizable ketones, and thiols under solvent-free conditions at room temperature to afford the corresponding β-aryl-β-mercaptoketones via aldol-Michael addition reactions. This methodology affords a large number of β-aryl-β-mercapto ketone derivatives in high yields and in short reaction times.     

Synthesis of the A,B,C-ring system of hexacyclinic acid

[structure: see text] The synthesis of the A,B,C-ring system (2) of hexacyclinic acid (1) is achieved starting from a selective Diels-Alder reaction followed by vinyl cuprate addition. The diastereoselective reduction of the ketone carbonyl at C16 could be achieved with LiAlH(4). An intramolecular Michael addition established the ring system stereoselectively, providing access to the selective generation of 9 out of the 14 stereocenters of hexacyclinic acid.     

The preparation of 1,4-dicarbonyl, 4-oxo nitrile,furan, and pyrrole monomers

Treatment of cyclopentadiene-blocked acrolein with α,β-unsaturated ketones, esters, and nitriles in the presence of a thiazoliurn salt under basic conditions led to a simple method for the preparation of acetonylmethyl Vinyl ketone, 2-carboxymethylethyl vinyl ketone, and 2-cyanoethyl vinyl ketone. In addition, the cyclopentadiene-blocked acetonylmethyl vinyl Ketone was converted to heterocyclic furan and pyrrole monomers.     

Cu-catalyzed enantioselective conjugate addition of alkylzincs to cyclic nitroalkenes: catalytic asymmetric synthesis of cyclic alpha-substituted ketones

An efficient and highly enantioselective (>/=92% ee) catalytic method for conjugate addition of alkylzinc reagents to cyclic nitroalkenes is reported. Reactions are promoted in the presence of 0.5-5 mol % (CuOTf)2.C6H6 and 1-10 mol % of chiral amino acid-based phosphine ligands at 0 degrees C in toluene. The Cu-catalyzed reactions can be effectively carried out with small-, medium-, and large-ring nitroalkenes. Depending on the reaction conditions used, either the nitro or the corresponding alpha-substituted ketone product can be readily accessed by the present protocol.     

Total synthesis of rhizoxin D,a potent antimitotic agent from the fungus Rhizopus chinensis

Rhizoxin D (2) was synthesized from four subunits, A, B, C, and D representing C3-C9, C10-C13, C14-C19, and C20-C27, respectively. Subunit A was prepared by cyclization of iodo acetal 21, which set the configuration at C5 of 2 through a stereoselective addition of the radical derived from dehalogenation of 21 at the beta carbon of the (Z)-alpha,beta-unsaturated ester. Aldehyde 29 was obtained from phenylthioacetal 24 and condensed with phosphorane 30, representing subunit B, in a Wittig reaction that gave the (E,E)-dienoate 31. This ester was converted to aldehyde 33 in preparation for coupling with subunit C. The latter in the form of methyl ketone 55 was obtained in six steps from propargyl alcohol. An aldol reaction of 33 with the enolate of 55 prepared with (+)-DIPCl gave the desired beta-hydroxy ketone 56 bearing a (13S)-configuration in a 17-20:1 ratio with its (13R)-diastereomer. After reduction to anti diol 57 and selective protection as TIPS ether 58, the C15 hydroxyl was esterified to give phosphonate 59. An intramolecular Wadsworth-Emmons reaction of aldehyde 62, derived from delta-lactone 60, furnished macrolactone 63, which was coupled in a Stille reaction with stannane 68 to give 2 after cleavage of the TIPS ether.     

The role of hydrogen bonds in Baeyer-Villiger reactions

Various Baeyer-Villiger (B-V) oxidation reactions were examined by density functional theory calculations. Proton movements in transition states (TSs) of the two key steps, the nucleophilic addition of a peroxyacid molecule to a ketone (TS1) and the migration-cleavage of O-O (TS3), were discussed. A new TS of a hydrogen-bond rearrangement in the Criegee intermediate (TS2) was found. The hydrogen-bond directionality requires a trimer of the peroxyacid molecules at the nucleophilic addition of a peroxyacid molecule to a ketone TS (TS1). At the migration-cleavage of O-O TS (TS3), also three peroxyacid molecules are needed. Elementary processes of the B-V reaction were determined by the use of the (acetone and (H-CO-OOH)n, n=3) system. The geometries of the nucleophilic addition of a peroxyacid molecule to a ketone TS (TS1) and the migration-cleavage of O-O TS (TS3) in the trimer (n=3) participating are nearly insensitive to the substituent on the peroxyacid. The directionality is satisfied in those geometries. The migration-cleavage of O-O TS (TS3) was found to be rate-determining in reactions, [Me2C=O+(H-CO-OOH)3], [Me2C=O+(F3C-CO-OOH)3], and [Me2C=O+(MCPBA)3]. In contrast, the nucleophilic addition of a peroxyacid molecule to a ketone (TS1) is rate-determining in the reaction, [Ph(Me)C=O+(H-CO-OOH)3].     

The role of Acid catalysis in the baeyer-villiger reaction. A theoretical study

Quantum mechanical calculations at the B3LYP/6-311+G(d,p) level have examined the overall mechanism of the Baeyer-Villiger (BV) reaction with peroxyacetic acid. A series of reactions that include both the addition step and the subsequent alkyl group migration step included ketones, acetone, t-butyl methyl ketone, acetophenone, cyclohexyl methyl ketone, and cyclohexyl phenyl ketone. The combined data suggested that the first step for addition of the peroxyacetic acid oxidation catalyst to the ketone carbonyl to produce the Criegee or tetrahedral intermediate is rate-limiting and has activation barriers that range from 38 to 41 kcal/mol without the aid of a catalyst. The rate of addition is markedly reduced by the catalytic action of a COOH functionality acting as a donor-acceptor group affecting both its proton transfer to the ketone C═O oxygen in concert with transfer of the OOH proton to the carboxylic acid carbonyl. The second or alkyl group migration step has a much reduced activation barrier, and its rate is not markedly influenced by acid catalysis. The rate of both steps in the BV reaction is greatly influenced by the catalytic action of very strong acids.     

Diastereoselective cyclopropanation of ketone enols with Fischer carbene complexes

Treatment of aryl/heteroaryl methoxycarbene complexes of chromium with -substituted ketone lithium enolates between -78 degrees C and room temperature resulted in the diastereoselective synthesis of 1,2,2,3-tetrasubstituted cyclopropanols. An exception has been observed in the reaction with cyclohexanone lithium enolate that yielded a bicyclic 2-buten-4-olide. 1,2-Dimethoxycyclopropanes and 1-methoxy-2-trimethylsilyloxycyclopropanes were isolated by quenching the reactions with MeOTf or Me3SiCl, respectively. This novel cyclopropanation process involves formation of lithium (3-oxoalkyl)pentacarbonylchromate intermediates which on warming undergo intramolecular addition to the carbonyl group. This cyclization is equivalent to the cyclopropanation in smooth conditions of electron-rich alkenes with Fischer carbene complexes.     

Copper(I)-catalyzed reaction of acylzirconocene chloride: cross-coupling and conjugate addition

For the purpose of exploring a new reaction of acylzirconocene chloride as an acyl anion donor, Cu(I)-catalyzed cross-coupling and conjugate addition reactions of acylzirconocene chloride were studied. The coupling reaction with allylic or propargylic halides efficiently proceeded to yield β,γ-unsaturated ketone or allenyl ketone derivatives, respectively. The conjugated addition reaction to ,β-enones was carried out in the presence of 2 equiv. of BF₃·OEt₂ giving 1,4-diketone compounds.     

Diastereoselective intramolecular Ritter reaction: generation of a cis-fused hexahydro-4aH-indeno[1,2-b]pyridine ring system with 4a,9b-diangular substituents

Indanol intermediates 5, prepared via Michael addition of 1-indanone beta-ketoester and acrylonitrile followed by reduction or Grignard reaction of the ketone group, were submitted to intramolecular Ritter reaction using various acid reaction conditions to produce tricyclic lactams 4. This cis-fused hexahydro-4aH-indeno[1,2-b]pyridine ring system, substituted at both angular positions 4a and 9b, provides access to constrained analogues of non-peptide NK(1)-antagonists with monocyclic piperidine structure.     

Direct enantioselective Michael addition of aldehydes to vinyl ketones catalyzed by chiral amines

Chiral amines such as (S)-2-[bis(3,5-dimethylphenyl)methyl]pyrrolidine and the C(2)-symmetric (2S,5S)-2,5-diphenylpyrrolidine can catalyze the direct enantioselective Michael addition of simple aldehydes to vinyl ketones. The conditions for this organocatalytic reaction have been optimized and it has been found that the chiral amines catalyze the formation of optically active substituted 5-keto aldehydes in good yields and enantioselectivities, using aldehydes and, e.g., methyl vinyl ketone as starting compounds. Taking into account that the chiral amine can activate the aldehyde and/or the enone, the mechanism for the reaction has been investigated. On the basis of intermediate synthesis, nonlinear effect, and theoretical investigations, the mechanism for the catalytic direct enantioselective Michael addition of aldehydes to vinyl ketones is discussed.     

Improved catalysts for the palladium-catalyzed synthesis of oxindoles by amide alpha-arylation. Rate acceleration, use of aryl chloride substrates, and a new carbene ligand for asymmetric transformations

Catalysts comprised Pd(OAc)(2) and either PCy(3) or sterically hindered N-heterocyclic carbene ligands provide fast rates for a palladium-catalyzed synthesis of oxindoles by amide alpha-arylation. This catalyst system allowed for room-temperature reactions in some cases and reactions of aryl chlorides at 70 degrees C. Most important, reactions occurred in high yields under mild conditions to form the quaternary carbon in alpha,alpha-disubstituted oxindoles. The combined inter- and intramolecular reaction afforded an efficient synthetic method for formation of alpha-aryloxindole derivatives. Surprisingly, catalysts containing tert-butylphosphine ligands, which have been most reactive for ketone arylations, were less active than those containing PCy(3). Use of new, optically active heterocyclic carbene ligands gave substantial enantioselectivity in formation of an alpha,alpha-disubstituted oxindole. In contrast, a variety of optically active phosphine ligands that were tested gave poor enantioselectivity. Mechanistic studies showed that the reaction involves rate-limiting oxidative addition of aryl halide. Base-induced formation of and reductive elimination from an arylpalladium enolate intermediate were both faster than oxidative addition. Deprotonation of the tethered amide appeared to be faster than reductive elimination of the resulting palladium enolate to form the oxindole product.     

Total synthesis of natural (+)-(2's,3'r)-zoapatanol

[reaction: see text] (+)-Zoapatanol was synthesized by using four key-steps: a Suzuki cross-coupling to prepare a (Z)-alpha,beta-unsaturated ester followed by an enantioselective dihydroxylation to control the C2' and C3' stereocenters, an intramolecular Horner-Wadsworth-Emmons olefination to construct the oxepane ring, and a chemoselective nucleophilic addition/Birch reduction process of a Weinreb amide to introduce simultaneously the beta,gamma-unsaturated ketone on the side-chain and regenerate alcohols from benzyl ethers.     

NiCl2(dppp)]-catalyzed cross-coupling of aryl halides with dialkyl phosphite, diphenylphosphine oxide, and diphenylphosphine

We present a general approach to C-P bond formation through the cross-coupling of aryl halides with a dialkyl phosphite, diphenylphosphine oxide, and diphenylphosphane by using [NiCl(2) (dppp)] as catalyst (dppp=1,3-bis(diphenylphosphino)propane). This catalyst system displays a broad applicability that is capable of catalyzing the cross-coupling of aryl bromides, particularly a range of unreactive aryl chlorides, with various types of phosphorus substrates, such as a dialkyl phosphite, diphenylphosphine oxide, and diphenylphosphane. Consequently, the synthesis of valuable phosphonates, phosphine oxides, and phosphanes can be achieved with one catalyst system. Moreover, the reaction proceeds not only at a much lower temperature (100-120?°C) relative to the classic Arbuzov reaction (ca.?160-220?°C), but also without the need of external reductants and supporting ligands. In addition, owing to the relatively mild reaction conditions, a range of labile groups, such as ether, ester, ketone, and cyano groups, are tolerated. Finally, a brief mechanistic study revealed that by using [NiCl(2) (dppp)] as a catalyst, the Ni(II) center could be readily reduced in situ to Ni(0) by the phosphorus substrates due to the influence of the dppp ligand, thereby facilitating the oxidative addition of aryl halides to a Ni(0) center. This step is the key to bringing the reaction into the catalytic cycle.     

Synthesis of allenes via palladium-catalyzed hydrogen-transfer reactions: propargylic amines as an allenyl anion equivalent

Synthesis of allenes has been achieved by using palladium-catalyzed hydrogen-transfer reactions. Various propargylic amines, which were readily prepapred from iodobenzenes and propargylic amines by Sonogashira coupling reaction, underwent the hydrogen-transfer reaction in the presence of Pd2dba3.CHCl3/(C6F5)3P catalyst at 100 degrees C in dioxane for 24 h, giving the corresponding allenes in 43-99% yields. Various propargylic alcohols containing a propargylic aminomethyl group, synthesized by the addition of lithium acetylides of N,N-diisopropylprop-2-ynylamine to aldehydes and a ketone, also underwent the hydrogen-transfer reaction in the presence of Pd2dba3.CHCl3 catalyst and (C6F5)3P at 80 degrees C in dioxane, giving the corresponding allenes in 56-92% yields. In the current transformation, propargylic amines can be handled as an allenyl anion equivalent and introduced into various electrophiles to be transformed into allenes under palladium-catalyzed conditions.