Telomerization Studies with Allyl Ethene Sulfonate and Allyl Allyl Sulfonate

Telomerization of allyl ethene sulfonate (AES) in the presence of butyl mercaptan yielded a mixture of two products: the first was a five-membered ring sultone containing a sulfide group and the second a five-membered ring sulfonium salt formed by reaction of the sultone of the Just product with its own sulfide function. If cyclotelomerizations and cyclopolymerizations give the same ring structures, these results indicate that the cyclic units in poly-AES are five-membered rings. Telomerization of allyl allyl sulfonate (AAS) in the presence of butyl mercaptan yielded a mixture of two products formed by addition of butyl mercaptan to one of the two allyl functions. Telomerization of AAS in bromotrichloromethane yielded a small amount of 1,5-hexachIoro-3-bromopentane formed via fission of an oxygen-carbon bond, and a rearranged adduct. The rearrangement of the allyl group to a propenyl group in the case of AAS was not observed when allyl ethane sulfonate or propyl allyl sulfonate were telomerized under the same conditions. Therefore a mechanism is proposed in which the rearrangement of the allyl double bond in AAS is due to the presence of a second double bond in the same molecule. This observation also indicates that poly-AAS might have a more complicated structure than expected from a simple cyclopolymerization mechanism.     

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.     

A short and efficient synthesis of 1,5-anhydro-d-glucitol 6-phosphate

The important d-glucose and d-glucose 6-phosphate analogues 1,5-anhydro-d-glucitol and 1,5-anhydro-d-glucitol 6-phosphate were prepared from methyl-d-glucoside in high yield and purity. Protecting of the hydroxyl groups as their allyl ether followed by reductive cleavage of the glycosidic linkage with triethylsilane formed the protected anhydroglucitol. No ring rearrangement or ring contraction was observed during the reduction step. Using the PdCl₂-CuCl₂-activated charcoal system, the allyl ether bond was cleaved with a low loading of the catalyst (0.0025 equiv per allyl group). 1,5-Anhydro-d-glucitol 6-phosphate was prepared by the phosphylation of 1,5-anhydro-d-glucitol.     

Synthesis of dialkyl(1-allyl-3-arylprop-2-yn-1-yl)-and dialkyl(1-allyl-3-alkenylprop-2-yn-1-yl)amines by the stevens rearrangement

The Stevens rearrangement of dialkyl(allyl)(3-arylprop-2-yn-1-yl)-and dialkyl(allyl)(3-alkenyl-prop-2-yn-1-yl)ammonium bromides gave dialkyl(1-allyl-3-arylprop-2-yn-1-yl)-and dialkyl(1-allyl-3-alkenyl-prop-2-yn-1-yl)amines. Here, the allyl group acts as migrating group, and 3-aryl-or 3-alkenylprop-2-yn-1-yl, as receiving one. The yields of the Stevens rearrangement products fall down as the alkyl chain becomes longer, as well as with introduction of a methyl group into the meta or para position of the aromatic ring.     

Dearomatization-bis-alkylation of aromatic and heteroaromatic diesters promoted by Me3SnLi via a stanna-Brook rearrangement

[STRUCTURE: SEE TEXT] Reaction of Me3SnLi with aromatic and heteroaromatic diesters proceeds through a fast stanna-Brook rearrangement that generates an stable bis-enolate which can be regioselectively alkylated and cyclized, in one step, to bicyclic compounds containing 6,5-, 6,6-, and 6,7-fused ring systems.     

Claisen rearrangement of allyl phenyl ether and its sulfur and selenium analogues on electron impact

The electron impact (EI) mass spectrum of allyl phenyl ether (1) includes an ion at m/z 106 that is formed mainly by the loss of CO from the molecular ion, as supported by high resolution and MS/MS data. The formation of the [M - CO](+) ion from 1 can be explained in terms of the Claisen rearrangement of 1 after ionization in the ion source of the mass spectrometer. Similarly, allyl phenyl sulfide (2) and allyl phenyl selenide (3) showed characteristic ions corresponding to [M - CH(3)](+), [M - XH](+) (X = S or Se) and [M - C(2)H(4)](+.), and the formation of these ions are explained via Claisen rearrangement of 2 and 3 in the ion source of the mass spectrometer resulting in a mixture of rearrangement products. The formation of molecular ions of 2-allyl thiophenol and 2-allyl selenophenol as intermediates, that cannot be isolated as the neutrals from the solution phase Claisen rearrangement of 2 and 3, respectively, is clearly indicated in the gas phase. The mass spectra of the rearrangement products obtained from the solution phase reaction were also consistent with the proposal of formation of these products in the ion source of the mass spectrometer. The formation of characteristic fragment ions attributed to the Claisen rearrangement products are also evident in the collision induced dissociation spectra of the corresponding molecular ions. Copyright 2000 John Wiley & Sons, Ltd.     

Rearrangements in the electron-impact induced fragmentation of some β-aroyl-α-methylpropionic acids

A complex rearrangement on electron-impact for β-aroyl-α-methylpropionic acids, involving both hydrogen and hydroxy migration followed by loss of carbon monoxide and allyl radical, is described and discussed. The rearrangement process, resulting in an ion [ArCOOH₂]⁺, is favoured by electron-withdrawing substituents in the aromatic ring.     

Intermolecular oxonium ylide mediated synthesis of medium-sized oxacycles

Detailed in this account are our efforts toward efficient oxacycle syntheses. Two complementary approaches are discussed, with both employing chemoselective allyl ether activation and rearrangement as the key step. Vinyl substituted oxiranes and oxetanes provide a single step access to dihydropyrans and tetrahydrooxepines. Oxiranes proved to be poor substrates, while oxetanes were slightly better. An alternative approach using substituted allyl ethers proved successful and addressed the limitations encountered in the ring expansions.     

Regio‐ and Stereospecific 1,3‐Allyl Group Transfer Triggered by a Copper‐Catalyzed Borylation/ortho‐Cyanation Cascade

A copper‐catalyzed borylation/ortho‐cyanation/allyl group transfer cascade was developed. Initiated by an unconventional copper‐catalyzed electrophilic dearomatization, this process features regio‐ and stereospecific 1,3‐transposition of the allyl fragment enabled by an aromatization‐driven Cope rearrangement. This method provides an effective means for the construction of adjacent tertiary and quaternary stereocenters with excellent diastereocontrol.     

Convenient Approach to 10- and 11-Membered Azalactams

A convenient method for the synthesis of 10- and 11-membered azalactams via reductive cleavage of bicyclic systems featuring an amidine fragment was studied. It was found that the ring-expansion reaction of bicyclic dihydropyrimidones depends on the ring size of saturated fragment, substituents in the pyrimidone core and reaction conditions. A new efficient method for the synthesis of medium ring azalactams by reductive cleavage of quaternary salts of annulated dihydropyrimidones was proposed as well. The obtained medium ring azalactams with a secondary amine function were used in the synthesis of bicyclic heteroaromatic systems.     

Le rearrangement de claisen en series siliciee et germaniee: silaethylene et germaethylene

Thermolysis of silicon and germanium isologues of allyl aryl ethers via transient metal π-bonded intermediates leads to aromatic Claisen-type rearrangement. Para-Claisen type reaction is not observed when the aromatic ring is ortho-disubstituted. In that case the Cope rearrangement is replaced by a radical process. The Claisen rearrangement leads to new oxametallacylohexanes by intramolecular trapping of the metal-carbon double-bond, when the homolytic process gives rise to new oxametallacycloheptanes.     

The diazo route to diazonamide A: studies on the tyrosine-derived fragment

Various approaches to the tyrosine-derived fragment of the marine secondary metabolite diazonamide A are described. Initial efforts were focused on the originally proposed structure of the natural product, and a feasibility study established that a model 4-aryltryptamine could be readily prepared. Protected 4-bromotryptamine underwent Pd0-catalyzed coupling with the boronic acid derived from 2-bromophenyl allyl ether by Claisen rearrangement, O-methylation and lithiation-boration. The resulting biaryl was elaborated into an alpha-diazo-beta-ketoester, dirhodium(II)-catalyzed reaction of which with N-Z-valinamide gave the desired tryptamine-oxazole following cyclodehydration of the intermediate ketoamide. A potential precursor to the benzofuran ring of the original structure of diazonamide A was prepared in eight steps from N-Z-tyrosine tert-butyl ester. Iodination, O-protection and Stille coupling gave the cinnamyl alcohol 25, converted via the bromide into the allyl aryl ether 27. Subsequent Claisen rearrangement and oxidative cleavage of the alkene gave the lactol 29, converted into the desired benzofuranone 31. The revision in the structure of diazonamide A to 2 resulted in the targeting of an alternative tyrosine-derived model benzofuranone 41 synthesized in four steps from N-Z-tyrosine methyl ester 36 by a route involving Claisen rearrangement of cinnamyl ether 37. Poor yields in this sequence prompted an investigation into the intramolecular Heck reaction as a route to benzofuranone 50. Coupling of 3-iodotyrosine 44 with 2-phenylbutenoic acid 48 gave ester 49 that readily underwent intramolecular Heck reaction to give benzofuranone 50, albeit with poor stereocontrol.     

Wittig rearrangement of allyl furfuryl and allyl thienyl ethers and sulfides and their benzo-derivatives

Treatment of allyl furfuryl ethers and sulfides with butyllithium results in metallation at the free -position of the heterocycle, with partial Wittig rearrangement to the isomeric alcohols and sulfides and ring opening. With the benzo-derivatives, Wittig rearrangement and ring opening takes place.Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 7, pp. 883–888, July, 1987.     

Stereocontrolled synthesis of cytotoxic anhydrosphingosine pachastrissamine by using [3.3] sigmatropic rearrangement of allyl cyanate

A new route for the synthesis of the cytotoxic anhydrosphingosine pachastrissamine has been developed. [3.3] Sigmatropic rearrangement of an allyl cyanate was employed to construct the allyl amine moiety in 2 from the chiral C-4 unit 3. Oxidative cleavage of the double bond in 2, followed by THF ring formation furnished the target pachastrissamine.     

A straightforward approach towards cyclic peptides via ring-closing metathesis--scope and limitations

N- and C-terminal diallylated peptides are obtained by several approaches, such as peptide Claisen rearrangement, N- and O- allylation, and the Ugi reaction of allyl-protected components. These diallylated peptides are suitable substrates for ring-closing metathesis and the success of this cyclisation was investigated with respect to the ring size, the position of the allyl moieties and the reaction parameters. In general, excellent yields are obtained for cyclisation of allyl glycine subunits and N-allylated amides, while allyl esters and allyl carbamates often presented serious problems. However, yields of up to 73% were obtained under optimised conditions, and the new generated double bond is formed with excellent trans-selectivity.     

A New Synthesis of Benzofurans from Phenols via Claisen Rearrangement and Ring‐Closing Metathesis

Based on Claisen rearrangement, the double bond isomerization of O‐allyl function together with the formation of O‐vinyl function in one pot, and ring‐closing metathesis (RCM), various phenols were transformed into various benzofurans in good yields.     

Conversion of imine ligands in allyl-nickel(II) complexes

Interaction of Ni(allyl)₂ and bidentate nitrogen-containing ligands (phenanthroline-1,10; bis(2,6-diisopropylphenyl)diazabutadiene) has been studied. It has been shown that coordination of diimine ligands proceeds with transfer of an allylnickel group to the diimine frame and formation of a covalent Ni-N bond giving rise to imine(amide)Ni(II) complexes. In the case of phenanthroline dearomatization of one heteroaromatic ring takes place. The low-spin imine(amide)allyl complexes (allyl)Ni(C₁₅H₁₅N₂) (1) and (allyl)Ni(C₂₉H₄₂N₂) (3) have been isolated as crystals and characterized by solution spectroscopy. Combining two molar equivalents of phenanthroline-1,10 with Ni(allyl)₂ results in the transfer of both allyl groups and formation of the high-spin imine(amide)Ni(II) complex Ni(C₁₅H₁₅N₂)₂ (2).     

Wagner–Meerwein rearrangement of [3.3.1] bicyclic N-Boc aminols: vinyl migration in preference to aryl migration

The Wagner–Meerwein rearrangement of [3.3.1] bicyclic N-Boc aminols was established, featuring the migration of the vinyl group instead of the aromatic ring. The structure of the rearrangement product was deduced through extensive spectroscopic studies and confirmed by the synthetic efforts. The scope of the reaction was examined and reasonably good yields were obtained for substrates with alkyl, allyl or benzyl substituent.     

Unusual dimroth rearrangement of an allyl-1,2,4-triazolo[4,3-c]pyrimidine

Refluxing 4-allyl-7-benzyl-5-methyl-1,2,4-triazolo[4,3-c]pyrimidine in an alcohol solution of sodium ethylate causes a Dimroth rearrangement together with a prototropic isomerization of the allyl fragment to give 7-benzyl-5-methyl-4-propenyl-1,2,4-triazolo[2,3-c]pyrimidine.Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 11, pp. 1545–1547, November, 1993     

Mechanism of 1,3-migration in allylperoxyl radicals: computational evidence for the formation of a loosely bound radical-dioxygen complex

The three pathways postulated for 1,3-migration of the peroxyl group in the allylperoxyl radical (1a), a key reaction involved in the spontaneous autoxidation of unsaturated lipids of biological importance, have been investigated by means of quantum mechanical electronic structure calculations. According to the barrier heights calculated from RCCSD(T)/6-311+G(3df,2p) energies with optimized molecular geometries and harmonic vibrational frequencies determined at the UMP2/6-311+G(3df,2p) level, the allylperoxyl rearrangement proceeds by fragmentation of 1a through a transition structure (TS1) with a calculated DeltaH++(298 K) of 21.7 kcal/mol to give an allyl radical-triplet dioxygen loosely bound complex (CX). In a subsequent step, the triplet dioxygen moiety of CX recombines at either end of the allyl radical moiety to convert the complex to the rearranged peroxyl radical (1a') or to revert to the starting peroxyl radical 1a. CX shows an electron charge transfer of 0.026 e in the direction allyl --> O(2). The dominant attractive interactions holding in association the allyl radical-triplet dioxygen pair in CX are due chiefly to dispersion forces. The DeltaH(298 K) for dissociation of CX in its isolated partners, allyl radical and triplet dioxygen, is predicted to be at least 1 kcal/mol. The formation of CX prevents the diffusion of its partners and maintains the stereocontrol along the fragmentation-recombination processes. The concerted 1,3-migration in allylperoxyl radical is predicted to take place through a five-membered ring peroxide transition structure (TS2) showing two long C-O bonds. The DeltaH++(298 K) calculated for this pathway is less favorable than the fragmentation-recombination pathway by 1.9 kcal/mol. The cyclization of 1a to give a dioxolanyl radical intermediate (2a) is found to proceed through a five-membered ring transition structure (TS3) with a calculated DeltaH++(298 K) of 33.9 kcal/mol. Thus, the sequence of ring closure 1a --> 2a and ring opening 2a --> 1a' is unlikely to play any significant role in allylperoxyl rearrangement 1a --> 1a'. In the three pathways investigated, the energy of the transition structure is predicted to be somewhat lower in either heptane or aqueous solution than in the gas phase. Although the energy lowering calculated for TS1 is smaller than the calculated for TS2 and TS3, it is very unlikely that the solvent effects may reverse the predicted preference of the fragmentation-recombination pathway over the concerted and stepwise ring closure-ring opening mechanisms.