Gold and Brønsted acid catalyzed hydride shift onto allenes: divergence in product selectivity

A series of allenyl ethers can be transformed into various fused or spiro tetrahydrofurans and tetrahydropyrans following a hydride shift/cyclization sequence. A divergence in product selectivity, which depends on the nature of the catalyst used (Au(I) complex or Br?nsted acid), was observed.     

Oxydation ausgewählter δ,ϵ- und ϵ,ξ-ungesättigter Alkohole mit Blei(IV)-acetat

The lead tetraacetate (LTA) oxidation of dihydro-γ-jonol ( 2 ) gives the new bicyclic ether 4 in high yield. On the other hand, LTA oxidation of the alcohols 8, 14, 20 , results in the formation of complex mixtures of oxidation products, from which the spiro compounds 10, 16, 22 , the bicyclic ethers 11, 12, 17, 18, 23 , and the carbonyl compounds 13, 19 have been isolated.     

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.     

BF3-promoted cyclization reaction of imines and salicylaldehyde with silyl enol ethers: unexpected formation of dioxaspiro compounds

Unexpected spiro cyclic products were formed from the reaction of imines and salicylaldehyde with silyl enol ethers in the presence of BF₃·OEt₂. Different kinds of dioxaspiro products were afforded depending on the nature of starting materials. Furthermore, salicylaldehyde could also react directly with several silyl enol ethers, giving three products with different spiro cyclic structure under the same reaction conditions.     

Addition of organochromium reagents to heteroaryl aldehydes. Synthesis of heteroaryl substituted bis-allyl ethers and homoallyl ethers

Heteroaryl substituted allyl and homoallyl alcohols were synthesised with two different method. Synthesis of bis-allyl ethers and homoallyl ethers were carried out via reaction of allyl bromide with allyl alcohols and homoallyl alcohols, respectively. [2.3]-Wittig Rearrangement reactions of heteroaryl substituted bis-allyl ethers were investigated using GC/MS techniques. In these reactions two unexpected products were isolated in high yield.     

Furans in Synthesis. The Preparation of Spiro-Cyclic Systems.

Furan-terminated cationic cyclizations allylic alcohols, enones, and N-acyl iminium ions as initiators have been explored as routes to highly functionalized spiro[4,5]decanes, spiro[5,5]undecanes, spiro[4,6]undecanes, and spiro[5,6]dodecanes.     

Palladium-catalyzed protection of alcohols and cleavage of triethylsilyl ethers

The versatility of the palladium (II) chloride/organosilane system has been tested in the transformation of alcohols to the corresponding silyl ethers and the subsequent deprotection of triethylsilyl ethers to the parent alcohols. The reaction takes place under mild conditions and affords high yields.     

脂肪族胺、醇、醚气相碱性的模型研究

以烷基极化效应指数(PEI)和分子中亲合原子的平衡电负性(XE)及亲合原子的Pauling电负性(X)为基本参数,研究了脂肪族胺、醇、醚的气相碱性(PA)的共同变化规律。结果表明,脂肪族胺、醇、醚的气相碱性可用下列通式来定量描述：PA(KJ/mol)=2468.6730+557.3172∑PEI-551.4261XE-1230.5770(∑PEI/XE)-111.5537X用上式预测了64种化合物的气相碱性,平均绝对相对误差仅为0.34%,预测值与文献值的偏差完全落在实验误差的范围内。     

Radical additions to 1,2-dichlorodifluoroethene

Fluorine containing alcohols, esters and ethers have been obtained by peroxide induced radical addition of alcohols, esters and ethers to 1,2-dichlorodifluoroethene.The influence of the kind and amount of the peroxide has been studied and the reactivity of alcohols, esters and ethers compared.     

Cascade radical cyclizations of benzannulated enyne-allenes. Unusual cleavage of a benzene ring leading to twisted 1,1'-dialkyl-9,9'-bifluorenylidenes and spiro[1H-cyclobut[a]indene-1,9'-[9H]fluorenes

Treatment of the benzannulated enediynyl propargylic alcohol 16 (isomer ratio = 2:1) with thionyl chloride induced a sequence of reactions leading to the twisted 1,1'-dipropyl-9,9'-bifluorenylidene 17, the polycyclic compounds 18 and 19, and the spiro[1H-cyclobut[a]indene-1,9'-[9H]fluorene] 20 (trans/cis = 5:1). The transformation from 16 to the unexpected 17 presumably involved an initial formation of the benzannulated enyne-allene 21 followed by a C(2)-C(6) cyclization reaction and an intramolecular radical-radical coupling reaction, giving rise to the formal Diels-Alder adduct 23. Repeat of this sequence then furnished 24. Cleavage of the bond connecting the two carbons having the propyl substituent afforded 25. A subsequent rotation of the carbon-carbon bond joining the two central five-membered rings then gave the trans isomer 26. Oxidation of 26, presumably by oxygen, followed by hydrolysis then produced 17. Interestingly, the pathway leading to 17 involved an unusual cleavage of a benzene ring. The X-ray crystal structure of 17 reveals that it has a twist angle of 45.2 degrees for the carbon-carbon double bond connecting the two bifluorenylidene fragments. The spiro[1H-cyclobut[a]indene-1,9'-[9H]fluorene] 20 apparently was produced via two intramolecular [2 + 2] cycloaddition reactions of the benzannulated enyne-allene moieties, generated in situ from the benzannulated enediynyl propargylic alcohols. The twisted 1,1'-dimethyl-9,9'-bifluorenylidene 33 and the spiro[1H-cyclobut[a]indene-1,9'-[9H]fluorene] 39 (trans/cis = 3:1) were likewise produced from 32 and 38, respectively.     

Trinitroethyl ethers of substituted alcohols

The influence of the trinitromethane salt cations and the substituents in the alkyl moiety of chloromethyl ethers of alcohols on the yields of trinitroethyl ethers of the substituted alcohols formed from them was established. On this basis a representative series of previously unavailable trinitroethanol ethers was synthesized.     

Efficient methods for the preparation of alkyl-aryl and symmetrical or unsymmetrical dialkyl ethers between alcohols and phenols or two alcohols by oxidation-reduction condensation

Oxidation-reduction condensation via alkoxydiphenylphosphines (diphenylphosphinite esters) (1), generated in situ from chlorodiphenylphosphine (2) and alcohols, 2,6-dimethyl-1,4-benzoquinone (3), and phenols proceeds smoothly to afford alkyl-aryl ethers in good to high yields under neutral conditions. In a similar fashion, a new and efficient method for the preparation of symmetrical or unsymmetrical dialkyl ethers in good to high yields is established via tetrafluoro-1,4-benzoquinone (fluoranil) (4), alcohols, and 1 formed in situ from (n)BuLi-treated alcohols and 2. This method is applicable also to the etherification of chiral secondary or tertiary alcohols with retention or inversion of configurations. The inverted ethers are afforded by treating chiral alkoxydiphenylphosphines and achiral alcohols, while the reaction of achiral alkoxydiphenylphosphines and chiral alcohols forms retained ethers.     

Organocatalytic,Enantioselective Synthesis of Cyclohexadienone Containing Hindered Spirocyclic Ethers through an Oxidative Dearomatization/Oxa‐Michael Addition Sequence

An unprecedented enantioselective oxa‐Michael reaction of α‐tertiary alcohols using cinchona‐alkaloid‐based chiral bifunctional squaramide catalysts is reported. An oxidative dearomatization of phenol followed by an enantioselective oxa‐Michael addition sequence provided a broad array of chiral sterically hindered tetrahydrofurans and tetrahydropyrans attached to a cyclohexadienone moiety in spiro fashion. In general, good yields and excellent enantioselectivities (up to 99 %) were observed. The chiral oxo‐cycles obtained have easily been transformed into chromans without disturbing the enantioselectivity.     

Organocatalytic,Enantioselective Synthesis of Cyclohexadienone Containing Hindered Spirocyclic Ethers through an Oxidative Dearomatization/Oxa‐Michael Addition Sequence

An unprecedented enantioselective oxa‐Michael reaction of α‐tertiary alcohols using cinchona‐alkaloid‐based chiral bifunctional squaramide catalysts is reported. An oxidative dearomatization of phenol followed by an enantioselective oxa‐Michael addition sequence provided a broad array of chiral sterically hindered tetrahydrofurans and tetrahydropyrans attached to a cyclohexadienone moiety in spiro fashion. In general, good yields and excellent enantioselectivities (up to 99 %) were observed. The chiral oxo‐cycles obtained have easily been transformed into chromans without disturbing the enantioselectivity.     

Exploratory Investigations Probing a Preparatively Versatile, Pyridinium Salt Photoelectrocyclization-Solvolytic Aziridine Ring Opening Sequence

A novel pyridinium salt photoelectrocyclization-nucleophilic bicyclic aziridine ring opening reaction sequence has been investigated in order to determine its preparative potential. N-Alkylpyridinium perchlorates were found to undergo photoinduced electrocyclization upon irradiation in nucleophilic solvents, such as H(2)O and MeOH, to efficiently produce 6-alkyl-6-azabicyclo[3.1.0]hex-2-en-4-yl alcohols and ethers. The bicyclic aziridine photoproducts react with a number of different nucleophiles (e.g., H(2)O, MeOH, AcOH, AcSH) under acid-catalyzed conditions to produce 5-(nucleophile-substituted)-4-(alkylamino)cyclopenten-3-yl alcohols and ethers. The aziridine ring opening processes are both regioselective and stereoselective, yielding trans,trans-trisubstituted cyclopentenes exclusively, apparently as a consequence of the operation of an SN(2) mechanism. The effects of C-alkyl substitution on the regiochemistry of the pyridinium cation photocyclization reaction were briefly probed, and a method was developed to produce trans,cis-trisubstituted cyclopentenes by use of this tandem preparative sequence.     

A dramatic difference between the electron-driven dissociation of alcohols and ethers and its relation to Rydberg states

A difference was observed in the reactivity of alcohols and ethers toward free electrons. Whereas the lowest core-excited state of the negative ion-a (2)(n,3s(2)) Feshbach resonance-of the alcohols readily dissociates by losing a hydrogen atom, ethers show no observable signal from this resonance. This difference in reactivity has a parallel in the anomalous shapes and energies of the parent states of the Feshbach resonances, the (1)(n,3s) Rydberg states of the neutral alcohols. We explained this anomaly using potential surfaces of the alcohols and ethers calculated using the TD-DFT method as a function of the dissociation coordinate. The lowest excited state of alcohols was found to be repulsive, whereas a barrier to dissociation was found in the ethers. Rydberg-valence mixing and avoided crossings are decisive in determining the shapes of the potential surfaces. It is concluded that the reactivities of alcohols and ethers toward free electrons are rationalized by assuming that the potential surfaces of the daughter Feshbach resonances closely follow those of the parent Rydberg states, i.e., the lowest Feshbach resonance is repulsive, but a barrier occurs in ethers. The potential surfaces of both the Rydberg states and the Feshbach resonances thus differ dramatically from the non-dissociative surface of the grandparent (2)(n(-1)) positive ions, despite the nominally non-bonding character of the Rydberg electrons.     

Synthesis of the C16-C35 fragment of integramycin using olefin hydroesterification as a linchpin reaction

[reaction: see text] The spiroketal unit of the HIV-integrase inhibitor integramycin has been prepared in an efficient and convergent manner. Key steps in this sequence include the use of ruthenium-mediated hydroesterification reactions of homoallylic alcohols and silyl ethers, and a C,O-dianionic addition into a lactone provides the spiroketal while minimizing protecting group manipulations.     

无催化剂下醇和酚的高效O-硅基化

硅醚类化合物广泛应用于有机合成、 分离分析和精细化工等领域. 六甲基二氮硅烷是近年来发展的一种新型硅基化试剂, 被用于硅醚的高效合成, 但由于六甲基硅烷较为惰性, 通常需要加入催化剂活化. 本文报道了一种无催化剂下醇、 酚的高效硅基化新方法. 研究结果表明, 该方法可以兼容一级苄醇、 杂芳基苄醇、 脂肪醇, 二级醇甚至三级醇, 多数反应可以实现定量转化, 无需柱层析即可实现产物的分离纯化. 该方法可以拓展到酚的高效硅醚化, 也可以很方便地放大到100 mmol, 收率达到99%, 表明该方法具有较好的实用价值.     

One-pot synthesis of 1,2-dihydropyridines: expanding the diverse reactivity of propargyl vinyl ethers

The catalyzed synthesis of 1,2-dihydropyridines starting from easily accessible propargyl vinyl ethers was realized. The reaction sequence involving a transition metal-catalyzed propargyl-Claisen rearrangement, a condensation step, and a Br?nsted acid-catalyzed heterocyclization furnishes the highly substituted heterocycles in moderate to excellent yields. Additionally, a practical one-pot protocol toward 1,2-dihydropyridines and 2H-pyrans starting from propargylic alcohols was developed.     

Sequential ring-closing metathesis and silicon-assisted cross-coupling reactions: stereocontrolled synthesis of highly substituted unsaturated alcohols

A sequential ring-closing metathesis/silicon-assisted cross-coupling sequence has been developed. Alkenyldimethylsilyl ethers of omega-unsaturated alcohols undergo facile ring closure with Schrock's catalyst to afford five-, six-, and seven-membered cycloalkenylsiloxanes bearing substituents on both alkenyl carbons. These siloxanes were highly effective coupling partners with various aryl and alkenyl halides and in the presence of Pd(0) afforded styrenes and dienes in high yield and specificity and with good functional group compatibility.