Catalyzed olefin isomerization leading to highly stereoselective Claisen rearrangements of aliphatic allyl vinyl ethers

Iridium(I)-catalyzed olefin isomerization in bis(allyl) ethers is integrated into a generally applicable strategy for affecting highly stereoselective Claisen rearrangements. Catalyzed alkene isomerization affords allyl vinyl ethers from easily prepared di(allyl) ethers; direct thermolysis of these reaction mixtures leads to highly diastereoselective [3,3] sigmatropic rearrangements affording syn-2,3-dialkyl-4-pentenal derivatives. An easily executed strategy for realizing asymmetric variants of the isomerization-Claisen rearrangement (ICR) reactions is also described.     

Synthesis and Reactions of New Vinyl Isothiocyanates

Abstract

New vinyl isothiocyanates, which can be prepared from easily accessible thiocyanates by [3,3] sigmatropic shifts, show unusually high reactivity used for the synthesis of heterocyclic sulfur compounds.     

Synthesis and rearrangement reactions of 1,4-dihydrospiro[1,4-methanonaphthalene-9,1′-cyclopropane] derivatives

Reactions of benzyne with ester derivatives of spiro[2.4]hepta-4,6-dien-1-ylmethanol were performed. By rearrangement reaction of cyclopropyl methanol units of ((1s*,1′R*,2R*,4′S*)-1′,4′-dihydrospiro[cyclopropane-1,9'-[1,4]methanonaphthalen]-2-yl) methyl 3,5-dinitrobenzoate (13) and its isomer (14), corresponding allyl chlorides were obtained. Two rearrangement products were obtained from bromination of compound 13 with an equivalent amount of Br₂. A naphthalene derivative including allyl and CHO moiety was formed for reactions from compounds with epoxide of 13 and 14 with NaN₃ by sequential rearrangements. Formations of products are discussed.     

2,4,8,10-Tetraoxa-3,9-diphosphaspiro[5.5]undecane-3,9-disulfide and Some Derived Compounds

2,4,8,10-Tetraoxa-3,9-diphosphaspiro[5.5]undecane-3,9-disulfide (I) has been prepared by the treatment of 3, 9-dichloro-2,4,8,10-tetraoxa-3,9-diphosphaspiro[5.5]undecane (II) with hydrogen sulfide. The reactions of I with thiocyanates to give esters of 3,9-dimercapto-2,4,8,10-tetraoxa-3,9-diphosphaspiro[5.5]undecane-3, 9-disulfide (III) and with isocyanates and isothiocyanates to give P-carbamoyl and thiocarbamoyl derivatives of I were investigated. I was also found to condense with chloral to produce an α-hydroxy-thiophosphonate (XXVIII), but similar reactions with other aldehydes failed to yield analogous products.     

Synthesis and reactions of pyrido[3,2,1‐jk]carbazole‐4,6‐diones

Pyrido[3,2,1‐jk]carbazoles 1 , synthesized from carbazoles and alkyl‐ or arylmalonates, gave regioselective electrophilic substitution reactions at position 5 such as chlorination to 5‐chloro derivatives 2 , nitration to 5‐nitro compounds 3 , or hydroxylation to 5‐hydroxy derivatives 4 . 5‐Hydroxy compounds 4 gave on treatment with strong bases ring contraction to 5 , 6 or the ring opening product 7 . Exchange of the chloro group in 2 with azide or amines gave the corresponding azides 8 and the 5‐amino derivatives 9 and 10 . Alkylation of 1 with benzyl chloride or allyl bromide resulted in the formation of 5‐C‐alkylated products 11 together with 4‐alkyloxy derivatives 12 . J. Heterocyclic Chem., 48, 1039 (2011).     

Transition Structures for the Aromatic Claisen Rearrangements by the Molecular Orbital Method

Ab initio calculations were performed for eight Claisen rearrangements, eqs 1-8. Transition-state (TS) structures of [3,3] sigmatropic rearrangements of reactions 1-4 are similar, but their activation energies (E(a)'s) are different, E(a)(1) < E(a)(2) and E(a)(3) < E(a)(4). From the intermediate of reaction 3, a hydrogen is moved intermolecularly to form the product, o-allyl phenol. The lower reactivities of reactions 2 and 4 relative to reactions 1 and 3 are ascribed to large endothermicities in the sigmatropic rearrangements, respectively. Chair-type transition states are more favorable than boat-type transition states in reactions 1-4. The allyl group is released from the in-plane C-X (X = O or N) sigma bond and is captured by the pi-type lone-pair electrons. The sulfur- and phosphorus-containing rearrangements, reactions 5-8, are computed to have smaller activation energies but are to be less exothermic than those of oxgyen- and nitrogen-containing rearrangements.     

Synthesis of alkynyl ethers and low-temperature sigmatropic rearrangement of allyl and benzyl alkynyl ethers

Alpha-alkoxy ketones 3 can be transformed into 1-alkynyl ethers 5 by a two-step procedure involving formation of the enol triflate or phosphate and base-induced elimination. Performing the same reaction sequence with allylic alcohols (R2OH, R2 = allyl) furnishes instead gamma,delta-unsaturated carboxylic acid derivatives 6, derived from [3,3]-sigmatropic rearrangement of the intermediate allyl alkynyl ethers at -78 degrees C and trapping of the subsequently formed ketene with nucleophiles (Nu-H). Benzyl alkynyl ether 5 (R2 = benzyl) rearranges to indanone 7 upon heating to 60 degrees C.     

Preparation and coordination properties including catalytic activities of a bulky 2-methyl-3-thioxo-1,3-diphosphapropene

[reaction: see text] 2-Methyl-3,3-diphenyl-3-thioxo-1-(2,4,6-tri-tert-butylphenyl)-1,3-diphosphapropene, which bears a P=C-P=S skeleton, was prepared and used as a ligand of transition-metal complexes. The palladium complexes containing the ligated 3-thioxo-1,3-diphophapropene were stable and used for catalytic reactions such as cross-couplings and direct conversion of allyl alcohol to allylaniline.     

Microwave-accelerated Claisen rearrangements of allyl tetronates and tetramates

[3,3]-Sigmatropic rearrangements of allyl tetronates and allyl tetramates to give 3-allyltetronic or -tetramic acids, respectively, proceed within 20-60 min under microwave irradiation (300 W, 130-190 °C). Consecutive (homo)sigmatropic [1,5] H-shifts such as oxa-ene reactions are promoted less effectively, which allows the isolation of Claisen intermediates of sigmatropic domino sequences, in contrast to conventional heating.     

Reaction of nitriles under acidic conditions. Part III. A facile synthesis of thienopyrimidin-4(3H)-ones

A variety of thiophene o-aminoesters were reacted with cyanates, thiocyanates, cyanamides, acyl cyanides and α-functionalized acetonitrile derivatives to yield the corresponding 2-substituted thienopyrimidin-4(3H)-ones.     

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).     

Hydrothermal Syntheses and Crystal Structures of Cobalt（Ⅱ） Complexes Constructed by Dipyrido[3,2-a：2＇,3＇-c]phenazine and Different Carboxylate Ligands

Two new metal-organic complexes,{[Co2(bptc)(DPPZ)2(H2O)2]·H2O}n 1 and {[Co2(ccm)2(DPPZ)2]·2H2O}n 2,were obtained by the hydrothermal reactions of Co(NO3)2·6H2O with chelating ligand dipyrido[3,2-a:2',3'-c]phenazine(DPPZ) and the corresponding carboxylic acid,namely,3,3',4,4'-benzophenonetetracarboxylic acid(H4bptc) or 2-carboxycinnamic acid(H2ccm),respectively.The complexes were structurally characterized by single-crystal X-ray diffraction,elemental analyses,IR spectra,and thermal gravimetry.1 presents unique chiral chain structures,which are further consolidated into three-dimensional supramolecular frameworks via noncovalent bonds,such as hydrogen bonding and π-π interactions.2 features infinite double-chain structures,which are connected by strong π-π interactions to result in three-dimensional supramolecular architectures.     

Aromatic glyoxalimines in criss-cross cycloaddition reactions

Aromatic 1,4-diazabuta-1,3-dienes in glacial acetic acid with thiocyanates produce via criss-cross cycloaddition reactions the corresponding perhydroimidazo[4,5-d]imidazole-2,5-dithiones. When a mixture of thiocyanate and cyanate in a proper ratio was reacted together, nonsymmetrical 5-thioxo-perhydroimidazo[4,5-d]imidazole-2-ones were isolated. With cyanates substituted aromatic 1,4-diazabuta-1,3-dienes afforded product of acetic acid addition to primary formed 1,3-dipole intermediate 5-(4-substituted phenylamino)-3-(4-substituted phenyl)-2-oxoimidazolidin-4-yl acetate.     

A convenient route to N-[2-(Fmoc)aminoethyl]glycine esters and PNA oligomerization using a Bis-N-Boc nucleobase protecting group strategy

A simple and practical synthesis of the benzyl, allyl, and 4-nitrobenzyl esters of N-[2-(Fmoc)aminoethyl]glycine is described starting from the known N-(2-aminoethyl)glycine. These esters are stored as stable hydrochloride salts and were used in the synthesis of peptide nucleic acid monomers possessing bis-N-Boc-protected nucleobase moieties on the exocyclic amino groups of ethyl cytosin-1-ylacetate, ethyl adenin-9-ylacetate and ethyl (O(6)-benzylguanin-9-yl)acetate. Upon ester hydrolysis, the corresponding nucleobase acetic acids were coupled to N-[2-(Fmoc)aminoethyl]glycine benzyl ester or to N-[2-(Fmoc)aminoethyl]glycine allyl ester in order to retain the O(6) benzyl ether protecting group of guanine. The Fmoc/bis-N-Boc-protected monomers were successfully used in the Fmoc-mediated solid-phase peptide synthesis of mixed sequence 10-mer PNA oligomers and are shown to be a viable alternative to the currently most widely used Fmoc/Bhoc-protected peptide nucleic acid monomers.     

Die Dienol-Benzol-Umlagerung von Allyldienolen: aromatische [1,2]-, [3,3]- und [3,4]-sigmatropische Umlagerungen

The dienol-benzene rearrangement of syn and anti-4-allyl-4-methylcyclohexa-2,5-dien-1-ol (syn and anti 15) occurs by formation of a benzonium ion intermediate in p-toluene-sulphonic acid in ether below 0° and leads to a mixture of 2-, 3- and 4-allyltoluenes in the ratio 54:10:36. By the introduction of ¹⁴C-, D- and methyl labelled dienols it is shown that only the allyl group migrates and that this rearrangement is an intramolecular, one-step process. The formation of 2-allyltoluene occurs with retention, whereas the 3- and 4-allyltoluenes are formed by inversion of the carbon skeleton of the migrating allyl group. These rearrangements can be therefore classified as suprafacial, aromatic sigmatropic reactions of the order [1,2], [3,3] and [3,4]. The transition state can be postulated as representing a positively charged complex consisting of interacting allyl and tolyl radicals. The interaction of the two parts is controlled by the symmetry of the highest occupied π-orbitals (ψ₃ for toluene and ψ₂ for the allyl group) in agreement with the Woodward-Hoffmann rules. The better “distribution” of the charge in the transition state of these reactions in comparison to the ground state is chiefly responsible for the CoPE-like [3,3] sigmatropic reaction occurring at low temperatures. In general, sigmatropic reactions in charged systems are faster. The rearrangement of syn and anti 2-allyl-2-methylcyclohexa-3,5-dien-1-ol (syn and anti 28) gives results similar to those obtained with the para-allyldienols. The thermal rearrangement of 15 and 28 gives 3-allyltoluene by a [3,3] sigmatropic Cope rearrangement followed by elimination of water.     

Novel rearrangements of sesquiterpenoid panasinsane derivatives under acidic conditions

The sesquiterpenoid panasinsane derivatives 11 and 14-16 have been prepared from caryophyllene oxide (7). The novel rearrangement reactions of compounds 11 and 14 under TCNE-catalyzed solvolysis conditions and the reactions of compounds 15 and 16 under superacid conditions (HSO3F/Et2O, -63 degrees C) have been investigated. The ginsenol derivative 17 is obtained from compounds 11 and 14 under TCNE-catalyzed conditions. The rearrangement of compounds 15 and 16 under superacid conditions leads to the novel sesquiterpene derivatives (1S,4S,7S,10S,11S)-3,3,10,11-tetramethyltricyclo[5.3.1.0(4,10)]undecan-1,11-yl sulfate (19) and (1S,4S,5S,8S)-2,2,4,8-tetramethyl tricyclo[3.3.2.1(4,8)]undecan-11-one (20). The influence of the secondary hydroxyl group at C-5 of the panasinsane derivatives on the course of these rearrangements is discussed.     

Synthesis of 1,2-Difunctionalized 1,3-Butadienes through a Sequence of Sigmatropic Rearrangements

Just by the introduction of isomerizable groups and successive [3,3] or [2,3] rearrangements, the diols 1 can be transformed into the new synthetic building blocks 2 . The conversion often proceeds with high stereoselectivity or even stereospecificity, and in some cases in a one-pot reaction. X, Y=NHCOCCl₃, N₃, P(O)Ph₂, 4-SO₂C₆H₄Me, S(O)Ar, SCOR.     

Selective reduction of tertiary alkyl,benzyl, and allyl halides to hydrocarbons using lithium 9,9-di-n-butyl-9-borabicyclo[3.3.1]nonanate

The title 9-borabicyclo[3.3.1]nonane(9-BBN) ate complex (1) brings about selective removal of tertiary alkyl, benzyl and allyl halides to give the corresponding hydrocarbons in excellent yields without concomitant attack on secondary, primary and aryl derivatives. The reduction of cis- and trans - 4 - t - butyl - 1 - methylcyclohexyl chlorides (2) with 1 gives 4 - t - butyl - 1 - methylcyclohexanes (3) with partial inversion of configuration in cyclohexane, while that in benzene gives thermodynamically stable trans-3 predominantly. The reactions of 1,1 - dimethyl - 5 - hexenyl chloride (4) and 1,7,7 - trimethylbicyclo[2.2.1]hept - 2 - yl chloride (8) with 1 proceed with the rearrangements characteristic to a carbonium ion intermediate. The reduction of 1 - ethyl - 1 - methylpentyl chloride with 1 follows a second-order rate equation.     

Formal [4 + 1]- and [5 + 1]-annulation by an S(N)2-conjugate addition sequence: stereoselective synthesis of highly substituted carbocycles

K(2)CO(3)-mediated reactions of 6-bromo-2-hexenoates and 7-bromo-2-heptenoate with active methylene compounds deliver highly substituted cyclopentane and cyclohexane derivatives, respectively via a sequence of S(N)2-conjugate addition reactions (formal [4 + 1]- and [5 + 1]-annulation) in a diastereoselective manner.     

Intramolekulare [2π + 2σ]-Thermo-cycloadditionen Synthese von Bis-homo-cyclopentadien-Derivaten Vorläufige Mitteilung

Intramolecular thermal [2π + 2σ]-cycloaddition reactions in the tricyclo[3.2.1.0^2,4]-oct-6-ene system are described. Within a certain set of conditions no [2π + 2σ]-additions within some tricyclo[5.1.0.0^3,5]octane derivatives could be achieved.