Transition‐Metal‐Free Borylation of Allylic and Propargylic Alcohols

The base‐catalyzed allylic borylation of tertiary allylic alcohols allows the synthesis of 1,1‐disubstituted allyl boronates, in moderate to high yield. The unexpected tandem performance of the Lewis acid–base adduct, [Hbase]⁺[MeO‐B₂pin₂]^? favored the formation of 1,2,3‐triborylated species from the tertiary allylic alcohols and 1‐propargylic cyclohexanol at 90 °C.     

Fragmentation of Homoallylic Alkoxides. Thermolysis of potassium 2-substituted bicyclo [2.2.2]oct-5-en-2-alkoxides

Thermolysis of the potassium 2-substituted bicyclo [2.2.2]oct-5-en-2-alkoxides derived from alcohols 2–17 at 90–120° in hexamethylphosphoric triamide affords unsaturated ketones resulting from allylic bond cleavage. The mechanistic and synthetic aspects of this anionic fragmentation are discussed with reference to the formation of 1-(3′-cyclohexenyl)-2-alkanones 18–28 via initial heterolytic C(1), C(2)-bond cleavage in the substrate alkoxide and regioselective, intramolecular protonation of the resultant transient allylic anion.     

Potassium Base-Promoted Diastereoselective Synthesis of 1,3-Diols from Allylic Alcohols and Aldehydes through a Tandem Allylic-Isomerization/Aldol–Tishchenko Reaction

This study reports the first base-promoted aldol–Tishchenko reactions of allylic alcohols with aldehydes initiated by allylic isomerization. The reaction enables the diastereoselective synthesis of a variety of 1,3-diols with three contiguous stereogenic centers. Unlike commonly reported systems, our method allows the use of readily available allylic alcohols as nucleophiles instead of enolizable aldehydes and ketones.     

Unraveling the Mechanism of the IrIII-Catalyzed Regiospecific Synthesis of α-Chlorocarbonyl Compounds from Allylic Alcohols

We have used experimental studies and DFT calculations to investigate the Ir^III-catalyzed isomerization of allylic alcohols into carbonyl compounds, and the regiospecific isomerization–chlorination of allylic alcohols into α-chlorinated carbonyl compounds. The mechanism involves a hydride elimination followed by a migratory insertion step that may take place at Cβ but also at Cα with a small energy-barrier difference of 1.8 kcal mol⁻¹. After a protonation step, calculations show that the final tautomerization can take place both at the Ir center and outside the catalytic cycle. For the isomerization–chlorination reaction, calculations show that the chlorination step takes place outside the cycle with an energy barrier much lower than that for the tautomerization to yield the saturated ketone. All the energies in the proposed mechanism are plausible, and the cycle accounts for the experimental observations.     

Photoredox-Catalyzed Isomerization of Highly Substituted Allylic Alcohols by C−H Bond Activation

Photoredox-catalyzed isomerization of γ-carbonyl-substituted allylic alcohols to their corresponding carbonyl compounds was achieved for the first time by C−H bond activation. This catalytic redox-neutral process resulted in the synthesis of 1,4-dicarbonyl compounds. Notably, allylic alcohols bearing tetrasubstituted olefins can also be transformed into their corresponding carbonyl compounds. Density functional theory calculations show that the carbonyl group at the γ-position of allylic alcohols are beneficial to the formation of their corresponding allylic alcohol radicals with high vertical electron affinity, which contributes to the completion of the photoredox catalytic cycle.     

Photoredox‐Catalyzed Isomerization of Highly Substituted Allylic Alcohols by C−H Bond Activation

Photoredox‐catalyzed isomerization of γ‐carbonyl‐substituted allylic alcohols to their corresponding carbonyl compounds was achieved for the first time by C?H bond activation. This catalytic redox‐neutral process resulted in the synthesis of 1,4‐dicarbonyl compounds. Notably, allylic alcohols bearing tetrasubstituted olefins can also be transformed into their corresponding carbonyl compounds. Density functional theory calculations show that the carbonyl group at the γ‐position of allylic alcohols are beneficial to the formation of their corresponding allylic alcohol radicals with high vertical electron affinity, which contributes to the completion of the photoredox catalytic cycle.     

Palladium-catalyzed alkylation of vinyl oxiranes with substituted allenes. Direct access to bifunctionalized allylic alcohols

The first palladium-catalyzed alkylation of vinyl oxiranes with substituted allenes to form functionalized allylic alcohols is described. The reaction of activated allenes 5 with vinyl oxiranes 1 in the presence of catalytic amounts of Pd(PPh(3))(4) (10 mol %) and 1,3-bis(diphenylphosphino)propane (dppp) (20 mol %) in THF at 60 degrees C gave the corresponding allylic alcohols 6 in good to excellent yields. The allylic alcohols were obtained in different ratios of trans/ cis isomers.     

Effets isotopiques du deutérium en RMN 13C,measure du marquage isotopique des alcools allylques.

Primary and secondary deuterium isotope effects on ¹³C NMR chemical shifts for trigonal carbons are reported for twelve allylic alcohols. The secondary DIECCS is used for an accurate measurement of the deuterium labeling of variously substituted allylic alcohols.     

Fragmentation of Homoallylic Alkoxides. Preparation of 1-(3′-cyclopentenyl)-2-alkanones from 2-substituted bicyclo[2.2.1]hept-5-en-2-ols

The potassium 2-substituted bicyclo[2.2.1]hept-5-en-2-alkoxides derived from alcohols 2–9 at 30° in hexamethylphosphoric triamide (HMPA) afford 1-(3′-cyclopentenyl)-2-alkanones 10–19 via heterolytic C(1), C(2)-allylic bond cleavage in the substrate alkoxide followed by intramolecular protonation of the resultant transient allylic anion.     

Competitive Silyl–Prins Cyclization versus Tandem Sakurai–Prins Cyclization: An Interesting Substitution Effect

Two different mechanism pathways are observed for the reaction of allylsilyl alcohols 1 and aldehydes in the presence of trimethylsilyl trifluoromethanesulfonate (TMSOTf). In the case of allylsilyl alcohols without allylic substituents, the reaction gives dioxaspirodecanes, which are the products of a tandem Sakurai–Prins cyclization. In contrast, allylsilyl alcohols with an allylic substituent (R²≠H) selectively provide oxepanes, thus corresponding to a direct silyl–Prins cyclization. Both types of product are obtained with excellent stereoselectivity. Theoretical studies have been performed to obtain some rationalization for the observed stereoselectivity.     

Direct palladium(0)-catalyzed amination of allylic alcohols with aminonaphthalenes

The direct activation of CO bonds in allylic alcohols by palladium complexes has been accelerated by carrying out the reactions in the presence of titanium reagents. The palladium-catalyzed amination of allylic alcohols using aminonaphthalenes gave N-allylic naphthylamines in good yields. The monoallylation products are formed in the main.     

Synthesis of 3-trifluoroethylfurans by palladium-catalyzed cyclization-isomerization of (Z)-2-alkynyl-3-trifluoromethyl allylic alcohols

Hydroiodonation of trifluoromethyl propargylic alcohols 1 regio- and stereoselectively produce (Z)-2-iodo-3-trifluoromethyl allylic alcohols 2. (Z)-2-Alkynyl-3-trifluoromethyl allylic alcohols 5, available through Pd(PPh3)4-mediated coupling of 2 and terminal alkynes 4, cyclize and subsequently isomerize to 3-trifluoroethylfurans 6 upon catalysis under PdCl2(CH3CN)2 in THF at 5-10 degrees C.     

Friedel-Crafts-type allylation of nitrogen-containing aromatic compounds with allylic alcohols catalyzed by a [Mo3S4Pd(η3-allyl)] cluster

With the direct use of allylic alcohols as allylating agents, the Friedel-Crafts-type allylic alkylation of nitrogen-containing aromatic compounds catalyzed by a [Mo(3)S(4)Pd(η(3)-allyl)] cluster is achieved. With a 3 mol % catalyst loading in acetonitrile at reflux or 60 °C, a variety of N,N-dialkylanilines and indoles reacted smoothly with allylic alcohols to afford the Friedel-Crafts-type allylation products in good to excellent yields with high levels of regioselectivity.     

Silicon‐Directed Rhenium‐Catalyzed Allylic Carbaminations and Oxidative Fragmentations of γ‐Silyl Allylic Alcohols

A highly regioselective allylic substitution of β‐silyl allylic alcohols has been achieved that provides the branched isomer as a single product. This high level of regiocontrol is achieved through the use of a vinyl silane group that can perform a Hiyama coupling providing 1,3‐disubstituted allylic amines. An unusual oxidative fragmentation product was also observed at elevated temperature that appears to proceed by a Fleming–Tamao‐type oxidation–elimination pathway.     

Kinetic resolution of allylic alcohols using a chiral phosphine catalyst

[reaction: see text] The kinetic resolution of racemic allylic alcohols 3, 6, and 12--17 has been explored using the PBO catalyst 7 for activation of isobutyric anhydride. Trisubstituted allylic alcohols (12--15; 17) are the best substrates and react with an enantioselectivity of s = 32--82 at -40 degrees C.     

Heterocyclic Spiro-naphthalenones. Part I: Synthesis and reactions of some spiro [(1 H-naphthalenone)-1,3′-piperidines]

The title compounds 14–16 were obtained via an intramolecular Mannich condensation by treating 11–13 with CH₂O at RT. The unsaturated ketones 14 and 15 were reduced to the allylic alcohols 18 and 19 respectively. Ring cleavage of compound 18 on treatment with 2N HCl gave the substituted aminopropanol 20 . The allylic alcohols 18 and 19 were hydrogenated to 22 and 23 respectively. With CH₂O, the amino-alcohol 23 gave the methano-naphthoxazocine 24 , whereas 22 and 23 , on heating in polyphosphoric acid (PPA), afforded the naphthazepines 25 and 26 respectively. With organolithium compounds, the unsaturated ketones 14 and 16 gave the teriary allylic alcohols 27–29 , which were hydrogenated and dehydrated to the olefins 36–40 ; these were cyclized via an intramolecular alkylation to the methanodibenzo-octahydrocyclooctapyridines 41–43 . On heating in PPA, the allylic alcohol 29 was converted into the naphthazepine 44 . With CH₂O, the naphthol 49 gave the naphthoxazocine 50 , in equilibrium with the spiro-naphthalene-pyrrolidinone 51 in solution. Finally, in the presence of CH₂O, the naphthazepine 57 afforded the methano-naphthazepinone 58 , which, by a 4-stage degradation, was transformed to the benzisoquinoline 62 .     

Facile One-pot Transformation of 2,3-Epoxy Alcohols into Allylic Alcohols

Optically-active allylic alcohols have been frequently used as chiral building blocks for the preparation of optically pure compounds.¹ There are at present various methods for the synthesis of optically active allylic alcohols including the kinetic resolution racemic allylic alcohols,² reductive rearrangement of 2,3-epoxy alcohol by metal, halide and telluium-based chemistry.³ To our knowledge, One-pot Transformation of 2,3-epoxy alcohols into allylic alcohols, especially via epoxy iodides,is limited to Dorta's method³ using a Ph₃P,iodine, imidazole,2,6-lutidine and water system. The original Dorta's method can be successfully applied to the formation of tertiary allylic alcohols, but give unsatisfactory results in formation of secondary allylic alcohols.     

Synthetic scope of Ru(OH)x/Al2O3-catalyzed hydrogen-transfer reactions: an application to reduction of allylic alcohols by a sequential process of isomerization/Meerwein-Ponndorf-Verley-type reduction

Reduction of allylic alcohols can be promoted efficiently by the supported ruthenium catalyst Ru(OH)x/Al2O3. Various allylic alcohols were converted to saturated alcohols in excellent yields by using 2-propanol without any additives. This Ru(OH)x/Al2O3-catalyzed reduction of a dienol proceeds only at the allylic double bond to afford the corresponding enol, and chemoselective isomerization and reduction can be realized under similar conditions. The catalysis is truly heterogeneous and the high catalytic performance can be maintained during at least three recycles of the Ru(OH)x/Al2O3 catalyst. The transformation of allylic alcohols to saturated alcohols consists of three sequential reactions: oxidation of allylic alcohols to alpha,beta-unsaturated carbonyl compounds; reduction of alpha,beta-unsaturated carbonyl compounds to saturated carbonyl compounds; and reduction of saturated carbonyl compounds to saturated alcohols.     

Palladium-catalyzed deracemization of allylic carbonates in water with formation of allylic alcohols: hydrogen carbonate ion as nucleophile in the palladium-catalyzed allylic substitution and kinetic resolution

The palladium-catalyzed deracemization of racemic cyclic and acyclic allylic methyl carbonates in water in the presence of N,N'-(1R,2R)-1,2-cyclohexanediylbis[2-(diphenylphophino)benzamide] proceeds with high enantioselectivities to give the corresponding allylic alcohols in high yields. This deracemization involves a palladium-catalyzed allylic substitution with the in-situ-formed hydrogen carbonate ion and an irreversible decomposition of the intermediate allylic hydrogen carbonates, with formation of the corresponding allylic alcohols. The palladium-catalyzed reaction of racemic cyclic allylic acetates with potassium hydrogen carbonate in water in the presence of the chiral bisphosphane proceeds with a highly selective kinetic resolution to give the corresponding allylic alcohols and allylic acetates.     

A novel acid-catalyzed C5-alkylation of oxindoles using alcohols

A novel C5-alkylation of oxindoles using alcohols as alkylating agents under acid catalysis is described for the first time. The reactions of various benzylic, allylic and propargylic alcohols are studied to obtain the corresponding 5-substituted oxindoles in good yields.