Organoboron compounds,synthesis of allyl(dialkyl)boranes and diallyl(alkyl)boranes

Highly reactive allyl(dialkyl)-, crotyl(dialkyl)-, 3,3-dimethylallyl(dialkyl)-(= prenyl(dialkyl), and diallyl(alkyl)-boranes were prepared by allylation of esters R₂BOR′, RB(OR′)₂ or thioesters R₂BSR′ (R = alkyl) using allylic derivatives of aluminium, magnesium or boron in exchange reactions.The titled compounds are stable up to 100°C and do not symmetrize even on heating at 100°C for a long time. PMR spectroscopy data show that the characteristic feature of these compounds is a permanent allyl rearrangement, the rate of which increases with an increase in temperature. For allyl(diethyl)-borane at 100°C and 125°C the rates are equal to 2500 and 5000 sec^?1 respectively; activation energy of the rearrangement amounts to 11.8±0.2 kcal mol^?1.The boronallyl bonds in unsymmetrical allyl(alkyl)boranes readily split under the action of water and alcohols, protonolysis being accompanied by allyl rearrangement, crotyl and prenyl compounds are converted into 1-butene or 3-methyl-1-butene, respectively.     

Umlagerung von Allyl-aryläthern und Allyl-cyclohexadienonen mittels Bortrichlorid

Allyl aryl ethers which have no strongly electron attracting substituents undergo a charge-induced [3 s, 3 s] sigmatropic rearrangement in the prescence of 0.7 mole boron trichloride in chlorobenzene at low temperature, to give after hydrolysis the corresponding o-allyl phenols (Tables 1 and 2). The charge induction causes an increase in the reaction rate relative to the thermal Claisen rearrangement of ～10¹⁰. With the exception of allyl 3-methoxyphenyl ether (5) , m-substituted allyl aryl ethers show similar behaviour (with respect to the composition of the product mixture) to that observed in the thermal rearrangement (Table 3). The rearrangement of allyl aryl ethers with an alkyl group in the o-position, in the prescence of boron trichloride, yields a mixture of o- and p-allyl phenols, where more p-product is present than in the corresponding product mixture from the thermal rearrangement (Table 4). This ‘para-effect’ is especially noticeable for o-alkylated α-methylallyl aryl ethers (Table 5 ). With boron trichloride, 2,6-dialkylated allyl aryl ethers give reaction products which arise, in each case, from a sequence of an ortho-Claisen rearrangement followed by a [1,2]-, [3,3]- or [3,4]-shift of the allyl moiety (Tables 6 and 7). Ally1 mesityl ether (80), with boron trichloride, gives pure 3-ally1 mesitol ( 95 ). From phenol, penta-ally1 phenol ( 101 ) can be obtained by a total of five O-allylations followed by three thermal and two boron trichloride-induced rearrangements. The sigmatropic rearrangements of the ethers studied, using D- and ¹⁴C-labelled compounds, are collected in scheme 2; only the reaction steps indicated by heavy arrows are of importance. With protic acids, there is a [3,3]-shift of the allyl group in 6-allyl-2,6-disubstituted cyclohexa-2,4-dien-l-ones, while with boron trichloride the [3,3]-reaction is also observed along with the much less important [1,2]- and [3,4]-transformations (Table 8). 4-Allyl-4-alkyl-cyclohexa-2,5-dien-1-ones give only [3,3]-rearrangements with boron trichloride (Table 9). As expected, the naphthalenone 112 , which is formed by allowing boron trichloridc to react for a short time with allyl (1-methyl-2-naphthyl) ether ( 111 ), undergoes only a [3,4] rearrangement (Scheme 3). Representations of how, in our opinion, the complex behaviour of allyl aryl ethers and allyl cyclohexadienones under the influence of boron trichloride, can be rationalized are collected together in Schemes 4 and 5. In the last part of the discussion section, the steric factors leading to the appearance of the ‘para-effect’, are dealt with (Scheme 6).     

Polymerization of allyl(vinyl phenyl) ethers and reactions of the resulting polymers

Solution polymerizations of allyl(o-vinyl phenyl)ether and allyl(p-vinyl phenyl)ether with cationic and radical initiators were investigated. Soluble polymers were formed in polymerizations with boron trifluoride etherate and with benzoyl peroxide. In polymerization with azobisisobutyronitrile the polymerization in dilute solution gave a soluble polymer, whereas that in concentrated solution gave a crosslinked, insoluble one. For informationon the polymerization behavior some infrared and ultraviolet spectroscopic investigations of the soluble polymers were made. From these results it appears that polymers with pendant allyl groups are formed in polymerization with boron trifluoride etherate at low temperature, and polymers containing pendant vinyl groups and allyl groups are obtained with the two types of radical initiator. Copolymerizations of these monomers with ethyl vinyl ether and styrene with the use of boron trifluoride etherate were sucessfully effected. Such reactions as Claisen rearrangement, crosslinking induced with radical initiators, and epoxidation with perbenzoic acid were examined for the polymers prepared in the polymerization with boron trifluoride etherate. Good results were obtained for the former two reactions. However, the latter was unsuccessful.     

On the action of amines and ammonia on triallylboron

Summary On treatment of triallylboron with ammonia or amines, diallyl(amino)boron or N-substituted derivatives thereof are formed.     

Regioselective boron trichloride-mediated aromatic Claisen rearrangement of resorcinol allyl ethers

The regioselective Claisen rearrangement of resorcinol allyl ethers with boron trichloride was achieved with good selectivity (ca. 13:1) to afford the 6-isomer as major product.     

Detection of Claisen Rearrangement Occurring in Allyl Phenyl Ether by in situ GC/MS

Itiswellknownthattheallylc0mP0undsexhibitavariety0finterestingrearrangementreacti0ns.Intheliquidphase,temPerature-inducedClaisenrearrangement,cyclizationreactionsandacid-induced0rthoClaisenrearrangementsofallylphenyletherhavebeenstUdiedextensively.'-'However,theClaisenrearrangementinthegasphasewasrepoftedonlyrecelltly,includingtheprotonatedallylphenyletherandN-allylanilineunderpositivecheITilcalionizationcondition4",thedeprotonatedallylphenylacetateanddeprotonatedallylphenyletherundernegati…     

Desymmetrization of Dicationic Diboranes by Isomerization Catalyzed by a Nucleophile

Cationic monoboranes exhibit a rich chemistry. By constrast, only a few cationic diboranes are known, that all are symmetrically substituted. In this work, the first unsymmetrically substituted dicationic diboranes, featuring sp²–sp²‐hybridized boron atoms, are reported. The compounds are formed by intramolecular rearrangement from preceding isomeric symmetrically substituted dicationic diboranes, a process that is catalyzed by nucleophiles. From the temperature‐dependence of the isomerization rate, activation parameters for this unprecedented rearrangement are derived. The difference in fluoride ion affinity between the two boron atoms and the bonding situation in these unique unsymmetrical dicationic diboranes are evaluated.     

A hierarchy of aryloxide deprotection by boron tribromide

Aryl propargyl ethers and esters are cleaved selectively in the presence of aryl methyl ethers and esters by boron tribromide in dichloromethane. Under the same conditions, allyl ethers undergo very rapid Claisen rearrangement, and benzyl ethers are also cleaved more rapidly than propargyl. A mechanism involving intramolecular delivery of bromide to the propargyl terminus is proposed. [reaction: see text]     

Dechalcogenative allylic selenosulfide and disulfide rearrangements: complementary methods for the formation of allylic sulfides in the absence of electrophiles. Scope, limitations, and application to the functionalization of unprotected peptides in aqueous media

Primary allylic selenosulfates (seleno Bunte salts) and selenocyanates transfer the allylic selenide moiety to thiols giving primary allylic selenosulfides, which undergo rearrangement in the presence of PPh3 with the loss of selenium to give allylically rearranged allyl alkyl sulfides. This rearrangement may be conducted with prenyl-type selenosulfides to give isoprenyl alkyl sulfides. Alkyl secondary and tertiary allylic disulfides, formed by sulfide transfer from allylic heteroaryl disulfides to thiols, undergo desulfurative allylic rearrangement on treatment with PPh3 in methanolic acetonitrile at room temperature. With nerolidyl alkyl disulfides this rearrangement provides an electrophile-free method for the introduction of the farnesyl chain onto thiols. Both rearrangements are compatible with the full range of functionality found in the proteinogenic amino acids, and it is demonstrated that the desulfurative rearrangement functions in aqueous media, enabling the derivatization of unprotected peptides. It is also demonstrated that the allylic disulfide rearrangement can be induced in the absence of phosphine at room temperature by treatment with piperidine, or simply by refluxing in methanol. Under these latter conditions the reaction is also applicable to allyl aryl disulfides, providing allylically rearranged allyl aryl sulfides in good yields.     

Note Synthesis and Characterization of Poly-(2-Methallyl-p-cresol)

In spite of the low reactivity of allyl monomers, attempts have been made to prepare polymers by polyrecombination of allyl aromatic compounds. We were encouraged by the stability of allyl radicals [1-8]. The literature on the Claisen rearrangement of polyfunctional allyl aryl ethers contains some observations of the formation of tarry masses and resinification of polyfunctional aryl ethers. Details of the polymerization and the possible structures were not studied. We felt it interesting to synthesize this new monomer, 2-methyallyl-p-cresol, by the rearrangement, and to study in detail the polymerization and characterization of the polymer.     

An isomerization—claisen rearrangement route to olefinic dicarbonyl starting materials for conjugate cyclization

Unsaturated dicarbonyl compounds which are useful in conjugate cyclization processes are synthesized by a route which makes use of a sequential isomerization and Claisen rearrangement of the allyl ether of a substituted allyl alcohol.     

Recent advances in the activation of boron and silicon reagents for stereocontrolled allylation reactions

Despite the popularity of boron and silicon allylation reagents in stereocontrolled synthesis, they suffer from a number of inherent limitations that have slowed down their development as synthetic tools for nucleophilic additions to carbonyl compounds and imine derivatives. These limitations are the low reactivity and diastereoselectivity of allyl trialkylsilane reagents, and the lack of catalytic systems for the activation and substoichiometric control of enantioselectivity in the additions of allyl boron reagents. To develop more efficient and general methods for the control of absolute stereochemistry in the resulting homoallylic alcohols, new approaches aimed at solving the problem of activation of allylic boron and silicon reagents are needed. This Minireview describes a number of recent approaches that have been devised to address this problem.     

Phosphite‐Catalyzed C−H Allylation of Azaarenes via an Enantioselective [2,3]‐Aza‐Wittig Rearrangement

A phosphite‐mediated [2,3]‐aza‐Wittig rearrangement has been developed for the regio‐ and enantioselective allylic alkylation of six‐membered heteroaromatic compounds (azaarenes). The nucleophilic phosphite adducts of N‐allyl salts undergo a stereoselective base‐mediated aza‐Wittig rearrangement and dissociation of the chiral phosphite for overall C?H functionalization of azaarenes. This method provides efficient access to tertiary and quaternary chiral centers in isoquinoline, quinoline, and pyridine systems, tolerating a broad variety of substituents on both the allyl part and azaarenes. Catalysis with chiral phosphites is also demonstrated with synthetically useful yields and enantioselectivities.     

Stereocontrolled Synthesis of Vinyl Boronates and Vinyl Silanes via Atom‐Economical Ruthenium‐Catalyzed Alkene–Alkyne Coupling

The synthesis of vinyl boronates and vinyl silanes was achieved by employing a Ru‐catalyzed alkene–alkyne coupling reaction of allyl boronates or allyl silanes with various alkynes. The double bond geometry in the generated vinyl boronates can be remotely controlled by the juxtaposing boron‐ and silicon groups on the alkyne substrate. The synthetic utility of the coupling products has been demonstrated in a variety of synthetic transformations, including iterative cross‐coupling reactions, and a Chan‐Lam‐type allyloxylation followed by a Claisen rearrangement. A sequential one‐pot alkene‐alkyne‐coupling/allylation‐sequence with an aldehyde to deliver a highly complex α‐silyl‐β‐hydroxy olefin with a handle for further functionalization was also realized.     

Synthetic route to 4-(2-aminoethyl)-5-hydroxyindole derivatives

In synthetic studies leading to the title compounds, application of the Claisen rearrangement of 5-allyloxyindole was investigated. Almost quantitative yields of Claisen rearrangement product were realized, and a strategy for oxidative cleavage of the allyl double bond to an indole-4-acetaldehyde derivative was developed. A new method for conversion of 2,3-dihydroindoles into indoles was utilized: air oxidation in a strongly basic environment. The Claisen rearrangement of allyloxyindoles is presented as a method having considerable potential utility in synthesis of a variety of polysubstituted indoles.     

Potassium Fluoride on Alumina: One-Pot Synthesis of Allyl Dithioesters by Tandem Condensation- Alkylation-Sigmatropic Rearrangement

Methylene ketones adsorbed on KF-alumina at room temperature react quickly with carbon disulfide and two equivalents of allyl chloride. The products undergo sigmatropic rearrangement, to give the corresponding allyl ketodithioesters.     

2-取代-3,4-二氢-1-异喹啉酮的合成和舒张血管活性

以3-羟基-4-甲氧基苯甲酸甲酯等为原料, 通过烯丙基醚化、Claisen重排、氧化、与伯胺反应(生成Schiff碱)、还原、分子内酯的胺解六步反应合成了一系列2-取代-3,4-二氢-1-异喹啉酮类化合物. Schiff碱的制备、还原、酯的胺解三步在“一锅”内完成. 采用1H NMR, MS和元素分析对目标化合物的结构进行了表征. 离体动脉环张力实验证明此类化合物具有明显舒张血管的作用.     

Formation of uncondensed binuclear heterocyclic compounds in the thio-claisen rearrangement of heteroaromatic sulfides

Allyl hetaryl Sulfides with an allyl fragment that is part of a heteroaromatic ring undergo a [3,3]-sigmatropic rearrangement when they are heated in various solvents, as a result of which uncondensed binuclear heterocyclic compounds are formed. On the basis of kinetic data it was shown that the inclusion of the vinyl or allyl fragment of a sulfide in the composition of the heteroaromatic ring hinders the rearrangement more, the higher the aromatic character of the heteroring.Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 10, pp. 1348–1351, October, 1983.     

Synthesis and Lewis acid catalyzed Claisen rearrangement of 2-(1,3-oxazolin-2-yl)-substituted allyl vinyl ethers

Allyl vinyl ethers containing an acceptor function in the 2-position are useful substrates for the Lewis acid-catalyzed Claisen rearrangement. The first synthesis of acyclic 2-(1,3-oxazolin-2-yl)-substituted allyl vinyl ethers is reported. The Lewis acid catalyzed Claisen rearrangement of these allyl vinyl ethers afforded the rearrangement products with low to moderate diastereo- and enantioselectivity. The catalyzed rearrangement of chiral allyl vinyl ethers was investigated. The combination of substrate- and catalyst-induced diastereoselectivity led to unexpected and unprecedented results.     

The Propargyl Rearrangement to Functionalised Allyl‐Boron and Borocation Compounds

A diverse range of Lewis acidic alkyl, vinyl and aryl boranes and borenium compounds that are capable of new carbon–carbon bond formation through selective migratory group transfer have been synthesised. Utilising a series of heteroleptic boranes [PhB(C₆F₅)₂ ( 1 ), PhCH₂CH₂B(C₆F₅)₂ ( 2 ), and E‐B(C₆F₅)₂(C₆F₅)C=C(I)R (R=Ph 3 a , nBu 3 b )] and borenium cations [phenylquinolatoborenium cation ([QOBPh][AlCl₄], 4 )], it has been shown that these boron‐based compounds are capable of producing novel allyl‐ boron and boronium compounds through complex rearrangement reactions with various propargyl esters and carbamates. These reactions yield highly functionalised, synthetically useful boron substituted organic compounds with substantial molecular complexity in a one‐pot reaction.