Mild and Efficient Synthesis of 1,8‐Naphthalide and 1,8‐Naphthalenedimethanol

Abstract

Mild and efficient procedures have been developed for synthesis of 1,8‐naphthalide and 1,8‐naphthalenedimethanol. In an ice‐water bath, 1,8‐naphthalide was prepared from 1,8‐naphthlic anhydride using LiAlH₄ as reducing agent. 1,8‐Naphthalenedimethanol was obtained with good yield from reduction of 1,8‐naphthalic anhydride by LiAlH₄ and Lewis acids at room temperature. The effects of various factors on the reduction of 1,8‐naphthalic anhydride with LiAlH₄ were investigated.     

Synthesis of 8-aryl-3,5,7,3′,4′-penta-O-methylcyanidins from the corresponding quercetin derivatives by reduction with LiAlH4

Synthesis of 8-aryl-3,5,7,3′,4′-penta-O-methylcyanidins from the corresponding quercetin derivatives by reduction with LiAlH₄ is reported. Regioselective iodination at the 8-position of penta-O-methylquercetin followed by a Suzuki-Miyaura reaction gave the 8-arylated quercetin derivatives. By the reduction of 8-arylated quercetins using 4 equiv. of LiAlH₄ at room temperature for 30 min, the corresponding anthocyanidins were obtained with a good yield.     

Reduction of Z-2-chlorostilbene with lithium aluminum hydride: evidence for an electron transfer radical mechanism

$\text{Z}$-2-Chlorostilbene undergoes uncatalyzed LiAlH₄ reduction giving phenanthrene and $\text{Z}$-stilbene. An electron transfer radical mechanism is proposed. LiAlH₄ induced isomerization of $\text{Z}$-stilbene produces $\text{E}$-stilbene.     

A new synthetic route to 3-polyfluoroalkyl-containing pyrroles

A novel approach to 3-polyfluoroalkyl pyrroles is reported based on step by step reactions: 1,2-addition of Me₃SiCN to β-alkoxyvinyl polyfluoroalkyl ketones, reduction with LiAlH₄ and subsequent hydrolysis with intramolecular cyclization. The hydrolytic instability of various polyfluoroalkyl groups at position 3 of the pyrrole ring was evident and a pathway for the hydrolysis was proposed.     

The influence of lithium complexing agents on the regioselectivity of reductions of substituted 2-cyclohexenones by LiAlH4 and LiBH4

A reversal of regioselectivity of LiAlH₄ or LiBH₄ reduction of 2-cyclohexenone induced by addition of [2.1.1]-cryptand to the reaction medium is accompanied by a rate decrease. In the absence of the cryptand, carbonyl attack predominates (C₁:C₃ = 86:14 with LiAlH₄ in THF). In the presence of the cryptand, double bond attack is favoured (C₁:C₃= 14:86). This effect is larger with LiAlH₄ than with LiBH₄. This trend is general in the case of five substituted 2-cyclohexenones. Using 12-crown-4 as a Li⁺ coordinator, a change in regioselectivity occurs but it is less pronounced than with the cryptand.     

Ein neuer Zugang zum tetracyclischen Grundgerüst des Cyclohepta (def)fluorens

A New Synthetic Way to the Tetracyclic Skeleton of Cyclohepta (def)fluorene The synthesis of 2-Methyl-4, 5, 6, 8, 9, 10-hexahydrocyclohepta (def)fluorene 2 is described starting with the reduction of the ketone 3 by a (1:1)-mixture of LiAlH₄/AlCl₃ to the hydrocarbon 4 . After metallation with butyllithium 4 was allowed to react with bromoacetic acid to yield 5 . The cyclization of this compound was performed with p-toluenesulfonic acid to give the tetracyclic ketone 6 which was converted to the tetracyclic hydrocarbon 2 by reduction with LiAlH₄/AlCl₃.     

Reduction of 5,6-Dimethylidene-exo-2,3-epoxynorbornane with Metal Hydrides. Efficient syntheses of 6-methyl-5-methylidene-anti-3- nortricyclanol and of 2,3-dimethylidene-anti-7-norbornanol

5,6-Dimethylidene-exo-2,3-epoxynorbornane ( 1 ) is reduced slowly by LiAlH₄ in boiling tetrahydrofuran (THF) and furnishes a mixture of 5,6-dimethylidene-exo-2-norbornanol ( 2 ), 2,3-dimethylidene-anti-7-norbornanol ( 3 ) and principally 6-methyl-5-methylidene-anti-3-nortricyclanol ( 4 ). The yield of 4 is the highest for low initial concentrations of LiAlH₄; it decreases in favour of alcohols 2 and 3 at high concentration of LiAlH₄. The reduction of 1 with AlH₃ in THF yields 3 as the major product, thus revealing an efficient synthesis of 7-substituted-2, 3-dimethyl-idenenorbornane derivatives. No alcohol 2 could be isolated by LiEt₃BH reduction of 1 . LiAlD₄ reduces 1 into the monodeuterated alcohols 2 -d, 3 -d and 4 -d. The deuterium label is found in the endo-position at C (3) in 2 -d, in the exo-position at C(5) in 3 -d and in the methyl group of the tricyclic alcohol 4 -d. Mechanistic limits for the formation of 2 , 3 and 4 are discussed briefly.     

Reduction of enedicarboxylate compounds with low valent titanium

The carbon—carbon double bonds of enedicarboxylate compounds can be reduced readily with TiCl₄LiAlH₄Et₃N in THF. Other double bond of the enedicarboxylate does not react during the reduction process.     

Syntheses of 2‐Unsubstituted 1H‐1,3‐Benzazaphospholes from N‐Formyl‐2‐bromoanilides

The phosphonylation of 2‐bromo‐formylanilides 1 with triethyl phosphite in the presence of preformed Pd(0)(triethyl phosphite)_n catalyst furnished 2‐phosphono‐formanilides 2 in good yields. Reduction with excess LiAlH₄ provided mainly N‐methyl‐2‐phosphinoanilines 3 and minor amounts of 1,2‐unsubstituted benzazaphospholes 4 . N‐Methyl‐1,3‐benzazaphospholes 5 were synthesized by the cyclocondensation of 3 with dimethylformamide dimethylacetal (DMFA). A more convenient route to 5 , avoiding the chromatographic separation of 4 , is the reduction of 1 to 2‐bromo‐N‐methylaniline 6 , followed by phosphonylation to 7 , LiAlH₄ reduction, and cyclization with DMFA. The coordination properties at σ²P of benzazaphospholes are characterized by structural data obtained by the crystal structure analysis of ( 5b )W(CO)₅.     

Lithium Aluminium Hydride and Metallic Iron: A Powerful Team in Alkene and Arene Hydrogenation Catalysis

Alkenes that normally do not react with LiAlH₄ (3-hexene, cyclohexene, 1-Me-cyclohexene), can be reduced to the corresponding alkanes by a mixture of LiAlH₄ and Fe⁰ (the iron was activated by Metal-Vapour-Synthesis). This alkene-to-alkane conversion with a stoichiometric quantity of LiAlH₄/Fe⁰ does not need quenching with water or acids, implying that both H's originate from LiAlH₄. The LiAlH₄/Fe⁰ combination is also a remarkably potent cooperative catalyst for hydrogenation of multi-substituted alkenes and benzene or toluene. An induction period of circa two hours and the minimally required temperature of 120 °C, suggests that the actual catalyst is a combination of Fe⁰ and the decomposition product of LiAlH₄ (LiH and Al⁰). A thermally pre-activated LiAlH₄/Fe⁰ catalyst did not need an induction time and is also active at room temperature and 1 bar H₂. A combination of AliBu₃ and Fe⁰ is an even more active hydrogenation catalyst. Without pre-activation, tetra-substituted alkenes like Me₂C=CMe₂ and toluene could be fully hydrogenated.     

Evidence for single electron transfer in the reduction of alcoholswith lithium aluminum hydride

EPR evidence supporting a single electron transfer mechanism in the reduction of secondary and tertiary alcohols to hydrocarbons with LiAlH₄ is presented.     

Reduction of glycyrrhizic acid

The reduction of glycyrrhizic acid by NaBH₄ and LiAlH₄ was studied. The conditions for the selective reduction of the COOH groups of the carbohydrate chain and the C(11)=0 group of aglycon were found. Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 4, pp. 875–877, April, 1997.     

Synthesis of 9-fluorenylmethoxycarbonyl-protected amino aldehydes

9-Fluorenylmethoxycarbonyl-protected amino aldehydes could be efficiently prepared in good yields by using two methods: (i) NaBH₄ reduction of Fmoc-protected mixed anhydrides, followed by the Swern oxidation of the alcohols; and (ii) LiAlH₄ reduction of Fmoc-protected amino acid Weinreb amides. Both methods afforded comparable overall synthetic yields (70–80%).     

Enantioselective Synthesis of Herbarumin III by Using a Chelation‐Controlled Reduction

The total synthesis of herbarumin III ( 1 ) was achieved via an alkynide ion addition onto a chiral aldehyde and LiAlH₄/LiI reduction as key steps (Scheme 2).     

Triaziridine. 6. Mitteilung. Substituententransformationen an Triaziridinen

Substituent Transformations on Triaziridines Several novel triaziridines were prepared by substituent transformations starting from the known dialkyl-triaziridine-carboxylates 1a – c , with the aim to study the influence of the substitution pattern on the properties of the triaziridine ring. The dialkyl-triaziridines 2a – c were obtained by (t-BuO^?)-mediated demethylation and decarboxylation and the dialkyl-triaziridine-methanols 4a – c by LiAlH₄ reduction. Further reduction of the tosylates of 4a , b with LiAlH₄ gave the methyl-dialkyl-triaziridines 3a , b . The dialkyl-triaziridines 2a , c could not be N-methylated directly with CH₃I, but the anions 10a , c , obtained from 2a, c with CH₃Li, yielded 3a , c . N-Methylation of 2a with (CH₃)₃OBF₄ did not afford 3a but rather the methyl-triaziridinium salt 11 . The dialkyl-triaziridine 2c has pK_a > 14, its protonated species < 2. A concept that the electron pairs on the triaziridine N-atoms are more strongly localized than on amine N-atoms explains (a) that the dialkyl-triaziridine 2c is hardly basic, (b) that the LiAlH₄ reductions of the esters 1 stop at the stage of the methanols 4 , and (c) that the methanols 4a , b do not cleave like aminomethanols.     

Reduction of aryl bromides with lithium aluminum hydride: Evidence for a radical mechanism

Reduction of $\text{0}$-bromophenyl allyl ether with LiAlH₄ yields phenyl allyl ether and 3-methyl-2,3-dihydrobenzofuran, thus suggesting the involvement of radical intermediates in the reduction.     

Preparation of a cross-linked polycarbosilane and its conversion to silicon carbide ceramics

Summary Cross-linked polycarbosilanes are obtained from the reaction of Cl₂MeSiCHCl₂ and Mg in tetrahydrofuran, followed by reduction with LiAlH₄. Analysis by NMR spectroscopy shows that most polycarbosilane is of the formula [MeSiCH]_n.Contribution no. 6627     

Études calorimétriques en milieu solvant organique: II Enthalpies de dissolution et de dilution du boranate de lithium (LiBH4) et de l'alanate de lithium (LiAlH4) dans le tétrahydrofuranne

The enthalpies of dissolution and dilution of LiBH₄ and LiAlH₄ in THF have been determined.Dissolutions are exothermic. The endothermic dilution of LiAlH₄ suggests for this compound, either a dissociation or an association equilibrium.     

In Situ Synthesis of 3D Flower‐Like Nanocrystalline Ni/C and its Effect on Hydrogen Storage Properties of LiAlH4

Lithium alanate (LiAlH₄) is of particular interest as one of the most promising candidates for solid‐state hydrogen storage. Unfortunately, high dehydrogenation temperatures and relatively slow kinetics limit its practical applications. Herein, 3D flower‐like nanocrystalline Ni/C, composed of highly dispersed Ni nanoparticles and interlaced carbon flakes, was synthesized in situ. The as‐synthesized nanocrystalline Ni/C significantly decreased the dehydrogenation temperature and dramatically improved the dehydrogenation kinetics of LiAlH₄. It was found that the LiAlH₄ sample with 10 wt % Ni/C (LiAlH₄‐10 wt %Ni/C) began hydrogen desorption at approximately 48 °C, which is very close to ambient temperature. Approximately 6.3 wt % H₂ was released from LiAlH₄‐10 wt %Ni/C within 60 min at 140 °C, whereas pristine LiAlH₄ only released 0.52 wt % H₂ under identical conditions. More importantly, the dehydrogenated products can partially rehydrogenate at 300 °C under 4 MPa H₂. The synergetic effect of the flower‐like carbon substrate and Ni active species contributes to the significantly reduced dehydrogenation temperatures and improved kinetics.     

Preparation d'alkyl-4 γ-lactones optiquement actives

Highly pure enantiomers of 4-alkyl γ-lactones are synthesized from optically active propargylic carbinols obtained by asymmetric reduction of α-acetylenic ketones with the chiral complex [LiAlH₄,N-methylephedrine-3,5 dimethylphenol].