An Efficient and Highly Chemoselective Method to Desilylate Silyl Ethers

An efficient and highly chemoselective desilylating method is described. Trimethylsilyl ethers (0.25 M) in a CH₃OH/CCl₄ (1:1) solvent mixture are deprotected to their corresponding alcohols with ultrasound in a commercial ultrasonic cleaning bath. Selective deprotection of tert-butyldimethylsilyl ethers of benzyl alcohols and phenols is achieved under ultrasonic conditions. We deprotected also tert-butyldimethylsilyl ethers of primary alcohols, whereas tert-butyldimethylsilyl ethers of secondary and tertiary alcohols are stable under these conditions.     

Synthesis of substituted tetrahydroisoquinolines and benzo[d]azepines from phthalan or isochroman and N‐silylaldimines

The 4,4′‐di‐tert‐butylbiphenyl‐catalyzed lithiation of phthalan ( 1a ) and isochroman ( 1b ) in THF at 0°C affords the corresponding functionalized benzyllithiums 2 , which by reaction with N‐silylaldimines yield, after acid‐base work‐up, the expected amino alcohols 3 . Successive treatment of these amino alcohols with thionyl chloride and sodium hydroxide yields the corresponding substituted benzofused six‐ and seven‐membered nitrogen‐containing heterocycles 4 .     

Acridin-9-ylmethoxycarbonyl （Amoc）： A New Photochemically Removable Protecting Group for Alcohols

Synthesis and photochemistry of acridin-9-ylmethoxycarbonyl(Amoc)as a new photochemically removableprotecting group for alcohols were described.Three carbonates of alcohols 1—3 were synthesized throughcondensation of 9-hydroxymethylacridine and chloroformates of alcohols,including benzyl alcohol,phenethylalcohol and one galactose derivative.The photolysis of protected alcohols can efficiently release the correspondingalcohol in the efficiencies(Q_(u1)ε)of 100—200(quantum yield Q_(u1)=0.011—0.023,and molar absorptivity ε=9.1×10~3—9.8×10~3 mol~(-1)·L·cm~(-1))under 360 nm light.     

Stereocontrolled enantioselective addition of diethylzinc to aldehydes using new chiral aminoalcohols

The new chiral β-aminoalcohols of indolinylmethanols ( 1 ) and their reduced derivatives ( 2 ) were synthesized from (S)-indoline-2-carboxylic acid. Both (R) and (S) enantiomers of the optically active secondary alcohols have been successfully obtained in high enantiomeric excess from the stereoselective addition of diethylzinc to the aldehydes catalyzed by the chiral aminoalcohols ( 1 and 2 ). The sense of the asymmetric induction and the degrees of enantioselectivities turned out to be highly dependent on the structure of the catalysts: The presence of the catalyst 1 afforded the (S)-configuration of the corresponding alcohols; on the other hand, the presence of 2 afforded the (R)-configuration of the alcohols in high enantiomeric selectivity.     

Photocatalytic Reduction of Nitro Compounds Using TiO2 Photocatalyst by UV and Vis Dye-sensitized Systems

Nitro‐aromatic compounds can be photocatalytically reduced into the corresponding amine‐aromatic compounds using TiO₂ as a photocatalyst in the UV/TiO₂/holes scavenger and Vis/TiO₂/dye‐sensitized systems. In the UV/TiO₂/holes scavenger system, reaction substrate alcohols such as methanol could be used as the holes scavengers, and in the Vis/TiO₂/dye‐sensitized system, substrate alcohols could be oxidized to the corresponding aldehydes with high selectivity. When methanol was used as the holes scavengers and the illumination time was 6 h, 87.2% of p‐nitrotoluene could be photocatalytically reduced into p‐toluidine. In the Vis/TiO₂/dye‐sensitized system, the effect of aromatic alcohols for the photocatalytic reduction of nitrobenzene was better than that of other alcohols. At the same time, aromatic alcohols can be easily oxidized, and the production efficiencies of the corresponding aldehydes were higher than those of other alcohols. The possible reaction mechanisms were also proposed.     

Reaction of 1-(alk-1-ynyl)-1-halocyclopropanes with alcohols and phenol in KOH/DMSO as a method for the synthesis of 2-alkoxy-1-alkynyl- and 1-alkynyl-2-phenoxycyclopropanes

The reaction of 1-(alk-1-ynyl)-1-halocyclopropanes with alcohols or phenol in KOH/DMSO at 80–100 °C leads to the corresponding alkynylalkoxy- and alkynylphenoxycyclopropanes in up to 80% yield. These reactions proceed through the intermediate formation of conjugated alkynylcyclopropenes capable of the in situ addition of alcohols at the double bond of the cyclopropene fragment. Regio- and stereoselectivity of the process is defined by the nature of substituents in the starting cyclopropanes and the structure of alcohols used.     

用Sharpless不对称双羟化反应合成手性β-氨基醇

以烯烃为原料合成了一组对映体纯的β-氨基醇．在手性配体1,4-双(9-O-奎宁)-2,3-二氮杂萘[(QN)₂PHAL]存在下, 通过烯烃的Sharpless不对称双羟化、环化、亲核开环和催化氢化等步骤方便地合成了手性β-氨基醇. 从环氧化物到氨基醇的总产率为89%～94%, β-叠氮醇和β-氨基醇的光学纯度高达90%～99% ee. 同时考察了影响环氧化物开环的各种因素．     

Camphor and Isocamphanone in the Synthesis of Disubstituted Acetylene Alcohols,Ethers, and Esters

By treating 1-octyne and phenylacetylene with butyllithium the corresponding lithium acetylides were obtained that with camphor and isocamphanone provided along streospecific process 2-exo-(1-octynyl or 2-phenyl-1-ethynyl)-2-endo-lithiumoxy-5,5,6-trimethylbicyclo[2.2.1]heptane and 2-endo-(1-octynyl or 2-phenyl-1-ethynyl)-2-exo-lithiumoxy-1,7,7-trimethylbicyclo[2.2.1]heptane. The hydrolysis of these lithium alcoholates occurred selectively and resulted in individual tertiary terpene alcohols containing exo-acetylene substituent in the case of camphor, endo-acetylene fragment in the case of isocamphanone. The alcohols reacted with methyl, ethyl, or butyl iodides in the presence of hexamethylphosphoramide to afford ethers, and with benzoyl chloride to furnish disubstituted esters of benzoic acid.     

Alcoholysis of 2,2-Dichloropropyl Derivatives of Carbazole, Phenothiazine, and Phenoxazine

Reactions of 9-(2,2-dichlorocyclopropyl)carbazole, 10-(2,2-dichlorocyclopropyl)phenothiazine, and 10-(2,2-dichlorocyclopropyl)phenoxazine with alcohols in the system t-BuOK-DMSO yield the corresponding N-(1-alkoxy-2-propynyl) derivatives. Hydrolysis of 9-(1-methoxy-2-propynyl)carbazole and 10-(1-methoxy-2-propynyl)phenothiazine in 60% aqueous dioxane in the presence of sulfuric acid gives the corresponding heterocyclic amine and 2-propynal.     

Enantioselective addition of EtzZn to aldehydes catalyzed by chiral aliphatic β‐amino alcohols

This paper describes the preparation of two new optically active aliphatic β‐amino alcohols (R)‐5,5‐dimethyl‐2–(dimethylamino)‐1, 1‐diphenyl‐1‐bersanol (la) and (S)‐8,8‐dimethyl‐2–(dimethylamino)‐1, 1‐diphenyl‐1‐nonanol (1b). They were synthesized by methylation of the corresponding β‐amino alcohols 2a and 2b. Compounds 1a and 1b catalyze the addition of diethylzinc to various aldehydes enantioselectivity. The catalyst structure‐enantioselectivity relationships were discussed.     

Asymmetric Synthesis of Monofluorinated Carbocyclic Alcohols and Vicinal Difluorinated Heterocycles and Carbocycles

A straightforward method to access novel families of enantioenriched cis-monofluorinated carbocyclic alcohols has been developed through ATH/DKR in up to 97 % yield, up to 99 : 1 dr and enantioinductions up to 97 % ee. Trans-difluorinated indans, tetrahydronaphthalenes, tetrahydroquinolines and chromans have been synthesized as well by deoxofluorination of the corresponding cis-fluoro alcohols. The reaction was performed on a series of variously substituted 3-fluorochromanols, 3-fluorotetrahydroquinolinols, 2-fluoro inden-1-ols and 2-fluoro 1,2,3,4-tetrahydronaphthalen-1-ols in up to 86 % yields, with diastereoselectivities up to 97 : 3 and enantioselectivities up to >99 % ee.     

Platinum‐Catalyzed Multi‐Step Reaction of Propargyl Alcohols with N‐Heteroaromatics

N‐Methyl indole reacts with but‐2‐yn‐1‐ol in the presence of PtCl₂ in MeOH giving indole derivatives having a substituted 3‐oxobutyl group at the 3‐position in good yield. Under the reaction conditions, various substituted indoles and substituted propargyl alcohols are successfully involved in the reaction giving the corresponding addition products in good to moderate yields. The catalytic reaction can be further extended to N‐phenyl pyrrole. In the present multi‐step reaction, PtCl₂ likely plays dual roles: as the catalyst for the rearrangement of propargyl alcohols to the corresponding alkenyl ketones and as the catalyst for the addition of indoles to the alkenyl ketones. Experimental evidence is provided to support the proposed mechanism.     

Temperature-dependent spectral changes of self-aggregates of zinc chlorophylls esterified by different linear alcohols at the 17-propionate

Systematically synthetic zinc 3-hydroxymethyl-13¹-oxo-chlorins esterified by different linear alcohols (methanol, 1-propanol, 1-hexanol, 1-dodecanol and 1-octadecanol) at the 17-propionate were self-assembled in the presence of cetyltrimethylammonium bromide in an aqueous solution. These zinc chlorins exhibited red-shifted Q _y absorption bands and circular dichroism (CD) signals in the corresponding Q _y region after incubation for 17 h, indicating that the zinc chlorins formed self-aggregates like those in natural chlorosomes of green photosynthetic bacteria. Visible absorption and CD spectra of self-aggregates of the zinc chlorins depended on the length of their esterifying alcohols. Zinc chlorins esterified by shorter alcohols gave larger changes in their visible absorption and CD spectra after incubation above 40°C, whereas zinc chlorins esterified by longer alcohols afforded smaller changes. These results indicate that hydrophobic interaction among esterifying chains of chlorin molecules as well as that between the esterifying chains and peripheral surfactants or lipids play an important role in the stability of chlorosomal self-aggregates.     

PREPARATION OF FORMIC ACID ESTERS WITH A PHOSPHONIUM SALT AND ZINC BROMIDE IN N,N-DIMETHYLFORMAMIDE

ABSTRACT

When primary and secondary alcohols were treated with the phosphonium salt 1 and ZnBr₂ in N,N-dimethylformamide, the corresponding formic acid esters were obtained in good yields.     

Synthetische Juvenilhormone 4. Mitteilung. p-Substituierte 5-Phenyl-penten(1)-carbonsäurederivate

The synthesis of p-substituted 2-methyl-5-phenyl-penten(1)-carboxylic acid derivatives is described: the formed Grignard compounds react with ethylene-oxide to the corresponding alcohols which are transformed by following reactions to the above mentioned compounds.     

Enantioselective Catalytic Borane Reduction of Prochiral Ketones: Synthesis and Application of New Rigid β-Amino Alcohols with a Cycloalkanol Subunit

Enantiocontrolled reduction of prochiral ketones with borane in the presence of new enantiomerically pure bi-and tricyclic β-sec-amino alcohols 2–5 as stereodifferentiating catalysts afforded the optically active corresponding secondary alcohols in moderate to excellent (up to 98 % op) optical yields.     

Synthesis ofo-andm-carborane derivatives of [2,2]paracyclophane and abnormal Clemmensen reduction of ketones of the [2,2]paracyclophane and carborane series

Methods for the synthesis of [2,2]paracyclophane derivatives containingo- andm-carboranyl substituents in position 4, separated from the [2,2]paracyclophane system by one or two C atoms (alcohols and ketones) were developed. The Clemmensen reduction of a number of ketones of the [2,2]paracyclophane ando-carbonane series occurs abnormally. The reduction of 1-benzoyl-o-carboranes to the corresponding alcohols by zinc in ethanol in a neutral medium was performed for the first time. Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 6, pp. 1206–1211, June, 1997.     

Stereoselective Synthesis of the Four Stereoisomers of 4-(N,N-Dibenzylamino)-2,2-dimethyl-3-hydroxypentanenitrile

The title compounds 1(a,b) and 1(c,d) were synthesized by (i) non-chelation controlled sodium borohydride reduction of their corresponding α-N,N-dibenzylaminoketones and (ii) the Aldol-type condensation of optically pure N,N-dibenzylaminoaldehydes with the lithium derivative of isobutyronitrile, respectively. Attempted inversion of configurations of these secondary alcohols using the Moriarty method yielded 4-chloro-3-N,N-dibenzylaminonitrile via an aziridinium ion intermediate instead of the expected inverted alcohols.     

Enantiodivergent Chemoenzymatic Dynamic Kinetic Resolution: Conversion of Racemic Propargyl Alcohols into Both Enantiomers

Natural lipases typically recognize enantiomers of alcohols based on the size differences of substituents near the carbinol moiety and selectively react with the R enantiomers of secondary alcohols. Therefore, lipase-catalyzed dynamic kinetic resolution (DKR) of racemic secondary alcohols produces only R enantiomers. We report herein a method for obtaining S enantiomers by DKR of secondary 3-(trialkylsilyl)propargyl alcohols by using a well-known R-selective Pseudomonas fluorescens lipase in combination with a racemization catalyst VMPS4, in which the silyl group reverses the size relationship of substituents near the carbinol moiety. We have already reported R-selective DKR of the corresponding propargyl alcohols without substituents on the ethynyl terminal carbon, and the presence of an easily removable silyl group has enabled us to produce both enantiomers of propargyl alcohols in high chemical yields and with high enantiomeric excess. In addition, immobilization of the lipase on Celite was found to be important for achieving a high efficiency of the DKR.     

Alcohol Dehydrogenases with anti-Prelog Stereopreference in Synthesis of Enantiopure Alcohols

Biocatalytic production of both enantiomers of optically active alcohols with high enantiopurities is of great interest in industry. Alcohol dehydrogenases (ADHs) represent an important class of enzymes that could be used as catalysts to produce optically active alcohols from their corresponding prochiral ketones. This review covers examples of the synthesis of optically active alcohols using ADHs that exhibit anti-Prelog stereopreference. Both wild-type and engineered ADHs that exhibit anti-Prelog stereopreference are highlighted.