Hydroxy Enones Research Articles

Highly Enantioselective Friedel—Crafts Alkylations of Pyrroles and Indoles with α′‐Hydroxy Enones under Cu(II)‐Simple Bis(oxazoline) Catalysis.

AbstractFor Abstract see ChemInform Abstract in Full Text.

Highly Enantioselective Friedel−Crafts Alkylations of Pyrroles and Indoles with α‘-Hydroxy Enones under Cu(II)-Simple Bis(oxazoline) Catalysis

Remarkably high and regular enantioselectivities are obtained in Friedel-Crafts alkylation reactions involving alpha'-hydroxy enone templates and Cu(II)-bis(oxazoline) complexes as catalysts. The simple elaboration of adducts provides a route to enantioenriched aldehydes, carboxylic acids, and ketones containing the pyrrole and indole frameworks.

Chemoenzymatic synthesis of both enantiomers of 4-acetoxy-2-hydroxymethyl-cyclohex-2-en-1-one

A chemoenzymatic synthesis of both enantiomers of the pharmacologically interesting 4-acetoxy-2-hydroxymethyl-cyclohex-2-en-1-one starting from cyclohexane-1,3-dione is described. Cyclohexane-1,3-dione was converted into 4,6,7,8-tetrahydro-benzo[1,3]dioxin-5-one and then manganese(III) acetate-mediated acetoxylation followed by the enzyme-mediated hydrolysis of α-acetoxy enone afforded the acetoxy enone and hydroxy enone with high enantiomeric excesses and in good yields. The reduction of the acetoxy enones furnished both enantiomers of 4-acetoxy-2-hydroxymethyl-cyclohex-2-en-1-one in high enantiomeric excess.

α′‐Hydroxy Enones as Achiral Templates for Lewis Acid‐Catalyzed Enantioselective Diels—Alder Reactions.

AbstractFor Abstract see ChemInform Abstract in Full Text.

A new and efficient chemoenzymatic route to both enantiomers of α ′-acetoxy-α-methyl and γ-hydroxy-α-methyl cyclic enones

A chemoenzymatic synthesis of both enantiomers of the pharmacologically interesting α ′-acetoxy-α-methyl and γ-hydroxy-α-methyl cyclic enones starting from α-methyl-β-methoxy cyclic enones is reported. Manganese(III) acetate-mediated acetoxylation followed by the enzyme-mediated hydrolysis of α ′-acetoxy enone provides acetoxy enones 1a and 2a and hydroxy enones 1b and 2b with high enantiomeric excesses in good yields. The reduction of the acetoxy and hydroxy enones furnished both enantiomers of γ-hydroxy-α-methyl cyclic enones 3 and 4 in a high enantiomeric excess.

Alpha'-hydroxy enones as achiral templates for Lewis acid-catalyzed enantioselective Diels-Alder reactions.

alpha'-Hydroxy enones react with dienes in the presence of (S,S)-[Cu(tBu-box)](OTf)2 or (S,S)-[Cu(tBu-box)](SbF6)2 (2 to 10 mol %) to afford the corresponding Diels-Alder adducts in high yield and selectivity. Isomeric ratios (regioselectivity, endo/exo or cis/trans) of up to >99:1 and ee values of up to >99% are obtained. Significantly, difficult dienes such as isoprene, 2,3-dimethyl butadiene and piperylene behave satisfactorily. Subsequent oxidative cleavage of the ketol in the resulting cycloadducts by treatment with cerium ammonium nitrate (CAN) yields the corresponding enantiopure carboxylic acids. Alternatively, carbonyl addition and subsequent diol cleavage with CAN produces the corresponding ketone adducts.

α′‐Hydroxy‐α,β‐unsaturated Tosylhydrazones: Preparation and Use as Intermediates for Carbonyl and Enone Transpositions.

AbstractFor Abstract see ChemInform Abstract in Full Text.

A new and efficient chemoenzymatic route to both enantiomers of 4-hydroxycyclohex-2-en-1-one.

[reaction: see text] A chemoenzymatic synthesis of both enantiomers of the pharmacologically interesting 4-hydroxycyclohex-2-en-1-one in three steps starting from 3-methoxycyclohex-2-en-1-one is described. Manganese(III) acetate-mediated acetoxylation followed by enzyme-mediated hydrolysis of alpha-acetoxy enone affords acetoxy enone 3 and hydroxy enone 4 with high enantiomeric excesses and in good yields. The reduction of the acetoxy and hydroxy enones furnished both enantiomers of 4-hydroxycyclohex-2-en-1-one in high enantiomeric excess.

A new and efficient chemoenzymatic access to both enantiomers of 4-hydroxycyclopent-2-en-1-one

A chemoenzymatic synthesis of both enantiomers of pharmacologically interesting 4-hydroxycyclopent-2-en-1-one in three steps starting from 3-methoxycyclopent-2-en-1-one is described. Manganese(III) acetate-mediated acetoxylation followed by enzyme-mediated hydrolysis of α-acetoxy enone affords acetoxy enone 3 and hydroxy enone 4 with high enantiomeric excesses and in good yields. The reduction of the acetoxy and hydroxy enones furnished both enantiomers of 4-hydroxycyclopent-2-en-1-one in high enantiomeric excess.

α′-HYDROXY-α,β-UNSATURATED TOSYLHYDRAZONES: PREPARATION AND USE AS INTERMEDIATES FOR CARBONYL AND ENONE TRANSPOSITIONS

ABSTRACT Regiospecifically generated α,β-unsaturated tosylhydrazones dianions are treated with molecular oxygen, yielding α′-hydroxy-α,β-unsaturated tosylhydrazones, versatile intermediates for organic synthesis. They proved to be useful for 1,2-carbonyl and 1,2-enone transpositions, and also permitted the preparation of α′-hydroxy enones in very high yields.

A new antiaromatic compound: 1,4-biphenylenequinone synthesis and trapping reactions: can a quinone unit stabilize the cyclobutadiene?

The photooxygenation of 4a,8b-dihydrobiphenylene affords an endoperoxide. NE t 3-catalyzed rearrangement of this endoperoxide gave the corresponding hydroxy enone, while the CoTPP-catalyzed rearrangement afforded a bisepoxide. MnO 2 oxidation of hydroxy enol leads to 4a,8b-dihydrobiphenylene-1,4-dione. The NBS bromination of this dione produces mono- and dibromides. NE t 3-supported elimination of monobromide and zinc elimination of dibromide afforded the target compound, 1,4-biphenylenequinone, which was trapped as the dimer and cycloadducts with cyclopentadiene and anthracene, respectively. Furthermore, 1,4-biphenylenequinone was generated upon oxidation of biphenylene-1,4-diol with bis(trifluoroacetoxy)iodobenzene (PIFA). The stability and reactivity of the title compound is discussed.

The first total synthesis of (±)-pallescensin B

The first total synthesis of the title compound has been accomplished using an intramolecular Diels–Alder reaction of a masked o-benzoquinone, anionic [1,3]-rearrangement of a vinylbicyclo[2.2.2]octenol and intramolecular hetero-Michael addition of a hydroxy enone as the key steps.

ChemInform Abstract: Studies Toward the Synthesis of Vinigrol. First Construction of the Tricyclic Ring System.

AbstractChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 100 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a “Full Text” option. The original article is trackable via the “References” option.

Studies toward the Synthesis of Vinigrol. First Construction of the Tricyclic Ring System

The first synthesis of a functionalized tricyclic skeleton of vinigrol is described. The key step involved an anionic oxy-Cope rearrangement of bicyclic allylic alcohol 18, readily prepared by highly stereoselective addition of vinyl magnesium chloride to the hydroxy enone 15b. Introduction of the tertiary hydroxy group at carbon 8a was achieved by an unexpected hydration of 30 with aqueous trifluoroacetic acid.

ChemInform Abstract: Complementary Facial Selectivity in Conjugate Additions to γ‐ Hydroxy Enones.

AbstractChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 100 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a “Full Text” option. The original article is trackable via the “References” option.

Diastereo- and enantioselective routes to some 2,8-dimethyl-1,7-dioxaspiro[5.5]undecanols. Absolute stereochemistry of (E,E,E)-2,8-dimethyl-1,7-dioxaspiro[5.5]undecan-3-ol and of (E,E)-8-methyl-1,7-dioxaspiro[5.5]undecan-2-yl)methanol present in Bactrocera cucumis

Routes to the four regioisomeric 2,8-dimethyl-1,7-dioxaspiro[5.5]undecanols have been developed, and in the racemic series, mercury(II)-mediated reactions of appropriate dienone, hydroxy enone, dienedione, and hydroxy dienone systems have been exploited. Most of the epimeric pairs of alcohols (i.e. axial or equatorial) in the EE, EE, or ZE spiroacetal ring systems have been characterized by detailed H, C, and correlated NMR spectroscopy and mass spectrometry. Key enantiomers of these alcohols have been obtained by elaborating chiral starting materials such as D-mannitol, L-arabinose, poly(hydroxybutyrate), and in the case of the 5-hydroxy derivative, mandelonitrile lyase mediated formation of a key chiral cyanohydrin was employed. Most of the alcohols, as their trifluoroacetates, are resolved (into enantiomers) on a Lipodex A GC column, thus facilitating their identification from natural sources. In this way, the absolute configurations of a number of 2,8-dimethyl-l,7-dioxaspiro[5.5]undecanols present in the rectal gland secretion of Bactrocera cucumis (cucumber fly) have been determined.

Ring A Modifications of Podocarpic Acid: Towards the Synthesis of Quassinoids

Efficient methods for the formation of the hydroxy enone moieties in (17), (18), (45) and (46) from podocarpic acid (1) have been developed. The exocyclic alkene (13) has been converted into the α-hydroxy enones (17) and (18) in six steps and high overall yield. Oxidation of the enones (7) and (44) with manganese(III) acetate gave high yields of the α-acetoxy enones (10) and (47) and (48), respectively. Hydrolysis of (10), (47) and (48) afforded the α-hydroxy enones (11), (45) and (46), respectively. Hydroboration-oxidation of the alkene mixture (38) and (41) provided the alcohol (53) (53%) which was readily oxidized to the ketone (21) (92%). This ketone (21) was converted in three steps into the hydroxy enone (57) in 39% overall yield. Hydroxylation of the enone (44) via the silyl dienol ether (58) gave the α- hydroxy enones (45) (16%) and (46) (33%). The stereochemistry of 12-methoxy-19-nor-5β-podocarpa-3,8,11,13-tetraen-2-one (44) was established by X-ray crystallography.

ChemInform Abstract: Electrophilic Condensation of Silyl Ethers of Homopropargyl Alcohols with Aldehydes. Regioselective Synthesis of Dihydropyrans.

AbstractThe homopropargylic alcohol (I) reacts with the aldehydes (II) in the presence of AlCl3 to give mixtures of the hydroxy enones (III) ‐ (V).

ChemInform Abstract: Diastereoselectivity in the TiCl4‐Mediated Aldol Reaction of Cyclic Dienylsilyl Ethers.

AbstractCyclic dienylsilyl ethers such as (I), derived from (R)‐(+)‐pulegone, undergo TiCl4‐catalyzed crossed aldol reactions with the aldehydes (II) to give the syn and anti hydroxy enones (III) and (IV) with good diastereoselectivity in the most cases.

An (S)-(+)-lactic acid route to (2S,6R,8S)-2,8 dimethyl-1,7-dioxaspiro[5,5]undecane and (2S,6R,8S)-2-ethyl-8-methyl-1,7-dioxaspiro[5,5]undecane and demonstration of their presence in the rectal glandular secretion of Bactrocera nigrotibialis(Perkins)

The chiral iodide resulting from reduction and iodination of the tetrahydropyran-2-yl ether of ethyl (S)-(+)-lactate has been engaged in a free-radical addition to acrylonitrile. The resulting protected hydroxy nitrite, on reaction with pent-4-enylmagnesium bromide afforded (S)-2-tetrahydropyran-2-yloxyundec-10-en-6-one. Oxymercuriation of this hydroxy enone, under reversible conditions, employing aqueous acid–tetrahydrofuran, effected simultaneous deprotection and cyclisation, and in situ biphasic demercuriation with sodium borohydride provided essentially stereochemically pure (2S,6R,8S)-2,8-dimethyl-1,7-dioxaspiro[5.5]undecane [i.e.the (E,E)-diastereoisomer only]. Epoxidation of the protected hydroxy enone, followed by dimethylcuprate ring-opening and cyclisation, provided a mixture of the (E,E)and the two possible (E,Z)-diastereoisomers of 2-ethyl-8-methyl-1,7-dioxaspiro[5.5]undecane with the former being the (2S,6R,8S) stereoisomer. Separation of the (E,E)from the two (E,Z)isomers was achieved by preparative gas chromatography. GC analysis of these samples and of the rectal glandular secretion of male Bactrocera nigrotibialis, using a cyclodextrin-based phase, demonstrated that the (2S,6R,8S)-stereoisomers of the 2,8-dimethyl- and 2-ethyl-8-methyl-1,7-dioxaspiro[5.5]undecanes were the natural products, with no detectable level of the antipodes.