Unexpected Rearrangement Research Articles

Rearrangement of a Bicyclo[3.2.0]hept‐2‐ene to a Bicyclo[4.1.0]hept‐4‐ene

AbstractThe chemistry of the highly substituted cyclobutanone derivative 2, which is easily accessible from 1, is dominated by the steric hindrance caused by the substitutents: Reduction with hydride reagents and nucleophilic additions with methyllithium are less stereoselective than corresponding reactions with less substituted bicyclo[3.2.0]hept‐2‐en‐6‐one derivatives, but under certain conditions, the exo product predominates, with methyl‐, benzyl‐, ethenyl‐, and ethynylmagnesium halides no nucleophilic addition at the carbonyl group is observed, presumably as a result of the steric hindrance. Instead, an unexpected rearrangement to the bicyclo[4.1.0]heptane carbon skeleton occurs with complete diastereoselectivity and high yields. The rearrangement is rationalized by an increase of the carbocationic character of the carbonyl carbon atom as a result of a coordination of the carbonyl oxygen atom at the Lewis acidic magnesium. This facilitates rearrangement of a cyclobutyl carbenium ion to a cyclopropylmethyl carbenium ion, the latter being stabilized by the amino group. Remarkably, with Grignard reagents derived from propargyl or allyl halides, no rearrangement is observed. The constitutions and configurations of the products were determined by 1H‐ and 13C‐NMR spectroscopy using techniques including NOESY and 2D‐INADEQUATE.

Unexpected rearrangement products from animations of 5‐bromo‐2‐nitrothiazole

AbstractWhile reaction of 2‐bromo‐5‐nitrothiazole (2) with weakly basic secondary aliphatic amines gives the expected 2‐amino products from nucleophilic displacement of the bromine, reaction of the isomeric 5‐bromo‐2‐nitrothiazole (3) with such amines gives mixtures of the expected 5‐amino products together with 2‐aminated 5‐nitrothiazole rearrangement products. The identity of the latter were detemined by alternative synthesis, and by X‐ray crystallographic determination of a derivative. The mechanism proposed is a slow thermal isomerization of 5‐bromo‐2‐nitrothiazole (3) to the much more reactive 2‐bromo‐5‐nitro isomer 2 which competes, in the case of relatively weak amine nucleophiles, with the direct (but slow) nucleophilic displacement of the 5‐bromo group to form the normal displacement products.

ChemInform Abstract: Unexpected Rearrangement of a Borneol‐Derived O‐Benzylated Hydroxamic Acid: Facile Synthesis of an Optically Active Multidentate Ligand.

AbstractChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 100 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a “Full Text” option. The original article is trackable via the “References” option.

ChemInform Abstract: Synthesis of Thiazole Compounds via Lithiation: An Unexpected Rearrangement.

AbstractChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 100 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a “Full Text” option. The original article is trackable via the “References” option.

Synthesis and Unexpected Rearrangement of a Hydroxyphostone (1)

Abstract During our investigations on the wide range of stereoselective alkylations of 6-membered ring phostones,1 we uncovered a novel rearrangement of 3-(diphenylhydroxymethyl)-2-ethoxy-2-oxo-1,2-oxaphosphorinane (1). The cis/trans diastereomers of 1 were prepared by the reaction of benzophenone with the appropriate ylide of the parent phostone (3).2 When trans- 1 was left unattended at rt in CH2Cl2 a new compound, 2, was isolated which showed a significant downfield 31P shift and a higher melting point. Upon heating to the melting point 2 decomposed to give 4, which suggests that 2 may be an intermediate in the conversion of 1 to the Wittig-like product 4. The IR, 1H, 13C, 31P, and 2-D NMR spectral data along with independent synthesis confirmed the identity of 2. Subsequently, 2 was also produced in 70% yield when cis- 1 was treated with CH2Cl2/ether-HC1aq at 50–60°C for 2 weeks, but this product was contaminated with 30% of the exocyclic alkene 5. No rearrangement was observed when 1 was treated with...

Synthesis of Vinca Alkaloids and Related Compounds. Part LXXXII. An Unexpected Neber-Type Rearrangement

Synthesis of Vinca Alkaloids and Related Compounds. Part LXXXII. An Unexpected Neber-Type Rearrangement

Cascade Rearrangement of 5-Cyclopentylidenecyclooctanones.

Acid-catalyzed rearrangement of 5-cyclopentylidenecyclooctanone derivatives 9a-c was examined to obtain polyspiropolyquinanes 11a-c, considered to have a unique helical structure, through cascade rearrangement pathways consisting of continuous transannular cyclization followed by successive 1,2-alkyl shifts. The substrates were prepared easily by use of the Wittig or McMurry reaction. Reaction of the 5-cyclopentylidenecyclooctanone (9a) with acid gave the expected dispirotriquinane ketone 11a in high yield. The precise mechanism was elucidated by a deuterium-labeling experiment. In the case of the ketone 9b, having another spiroannulated cyclopentane ring attached on 9a, the trispirotetraquiane 11b was not obtained but the bis-propellane-type tetrahydrofuran 25 was produced exclusively. The 5-(5'-cyclopentylidenecyclooctylidene)cyclooctanone (9c) afforded the polycyclic compounds 27-31, depending on the acid used, instead of the desired tetraspiropentaquinane 11c. The structures of the products were determined by NMR spectral data including 2D (13)C INADEQUATE spectra and X-ray crystallographic analyses. The unexpected rearrangement pathways are also discussed.

Unexpected Rearrangement of a Borneol-Derived O-Benzylated Hydroxamic Acid: Facile Synthesis of an Optically Active Multidentate Ligand

Unexpected Rearrangement of a Borneol-Derived <i>O-</i>Benzylated Hydroxamic Acid: Facile Synthesis of an Optically Active Multidentate Ligand

ChemInform Abstract: Unexpected Rearrangement in the Peroxytrifluoroacetic Acid‐Mediated Baeyer‐Villiger Oxidation of trans‐3β‐Hydroxy‐4,4,10β‐ trimethyl‐9‐decalone Forming a 7‐Oxabicyclo(2.2.1)heptane. Structure Proof and Total Synthesis of (.+‐.)‐Farnesiferol‐C.

AbstractChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 100 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a “Full Text” option. The original article is trackable via the “References” option.

Synthesis of thiazole compounds via lithiation: an unexpected rearrangement

A novel rearrangement was discovered during an investigation of the lithium-bromine exchange reactions of bromothiazole derivatives and their subsequent reactions with various electrophiles.

Unexpected Rearrangement in the Peroxytrifluoroacetic Acid-Mediated Baeyer-Villiger Oxidation of trans-3.beta.-Hydroxy-4,4,10.beta.-trimethyl-9-decalone Forming a 7-Oxabicyclo[2.2.1]heptane. Structure Proof and Total Synthesis of (.+-.)-Farnesiferol-C

Unexpected Rearrangement in the Peroxytrifluoroacetic Acid-Mediated Baeyer-Villiger Oxidation of trans-3.beta.-Hydroxy-4,4,10.beta.-trimethyl-9-decalone Forming a 7-Oxabicyclo[2.2.1]heptane. Structure Proof and Total Synthesis of (.+-.)-Farnesiferol-C

Unexpected ionic rearrangement of hypoiodite. Ring-expansion of 4-alkynyl-4-hydroxycyclobutenone to iodomethylenecyclopentene-1,3-dione

While hypoiodites generally produce oxy-radical intermediates upon photolysis or thermolysis, the reaction of 4-alkynyl-4-hydroxycyclobutenones with I2/HgO, I2/PhI(OAc)2 and NIS all believed to form a hypoiodite afforded, even at room temperature, iodomethylenecyclopentene-1,3-diones as rearranged products via an ionic pathway.

MONO-η6-ARENE COMPLEXES OF CHROMIUM (II) AND CHROMIUM (0). ARENE EXCHANGE AND ARENE DISPLACEMENT REACTIONS OF η6-FLUOROARENE-DICARBONYLBIS (TRICHLOROSILYL) AND -TRICARBONYLCHROMIUM DERIVATIVES

Abstract In an attempt to obtain chromium-arene derivatives possessing high arene lability, (C6 H5F)Cr(CO)2 (SiCl3)2, (C6H4F2)Cr(CO)2(SiCl3)2, (C6H5F)Cr(CO)3, and (C6H4F2)Cr(CO)3 have been investigated. Kinetics of arene exchange have been studied showing that the Cr(II) derivatives exhibit ten-fold higher rates than the Cr(O) derivatives. Both electronic and steric effects appear to be important, although electronic effects dominate. Arene displacement by phosphine and phosphite ligands has also been studied. Although arene displacement took place, unexpected rearrangement and disproportionation reactions occurred yielding seven-coordinate (CO)4Cr(PR3)(SiCl3)2 species.

Unusual Rearrangement in the Photochemical Addition of Bis(alkylidene)disilacyclobutanes to C60

The photochemical reaction of bis(alkylidene)-disilacyclobutanes 1a, b with C[sub 60] afforded the stable 1:1 adducts 3a,b, resulting from an unexpected rearrangement of the disilacyclobutane unit. The structures of 3a,b were determined by spectroscopic methods, including [sup 29]Si-[sup 1]H HMBC hetero nuclear shift correlation experiments. 18 refs., 2 figs.

Reaction of Glycosyl Halides with Benzyl Grignard Reagents: Unexpected o-Tolyl Alkylation of Tetra-O-acetylglucopyranosyl Bromide and Direct Synthesis of (B-Glycosyl)phenylmethanes

Abstract The synthesis of (β-glycosyl1)phenylmethanes by Grignard alkylation of glycosyl halides is investigated. Reaction of tetra-O-acetylglucopyranosyl bromide with benzylmagnesium chloride gave a good yield of a 3:1 mixture of 2-(β-d-glucopyranosyl)toluene and (β-glucosyl)phenylmethane. The requirement for an equatorial 2-acetoxy group and 6-acetoxymethyl group for the formation of the unexpected o-tolyl rearrangement product is explored by using xylosyl, mannosyl, and 2-deoxyglucosyl halides as substrates for the alkylation. Synthesis of (β-glucosyl)phenylmethane by alkylation of 2,3,4,6-tetra-O-benzylglucosyl bromide with benzylmagnesium chloride is also presented.

ChemInform Abstract: Silicon Compounds with Strong Intramolecular Steric Interactions. Part 52. Unexpected Rearrangement of Silylene Insertion into Cycloaddition Products.

AbstractChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 100 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a “Full Text” option. The original article is trackable via the “References” option.

Stereochemistry. 83. Unusual rearrangements in cage compounds due to proximity effects

The strained keto diol 5 underwent an unexpected rearrangement in the presence of H 2 O-TEA-CH 3 CN at 20 o C to afford two isomeric product 6 and 7. The latter two compounds undergo further conversion to carboxy keto diol 8. The structures of 6-8 were elucidated by heterero COSY experiments and in the case of 6 by X-ray diffraction. The transformation of 5 to 6 and 7 is interpreted as involving an unusual retroaddition of a benzylic anion to a cyclobutanone 5→10. This is facilitated by subsequent readdition of this anion to another proximally located ketone with formation of a cyclopropanol 11, which is immediately converted to 6 and 7

Silicon compounds with strong intramolecular steric interactions. 52. Unexpected rearrangement of silylene insertion into cycloaddition products

Silicon compounds with strong intramolecular steric interactions. 52. Unexpected rearrangement of silylene insertion into cycloaddition products

Unexpected acid-catalysed rearrangement of a vinylcyclopropane derivative

A vinylcyclopropane carboxylic acid derivative undergoes a novel type of rearrangement under mild acidic conditions; X-ray diffraction study of the rearrangement product confirms the structure as (1SR,4SR,7SR)-4-methyl-3,9-dioxabicyclo[5.3.0]dec-5-ene-2,10-dione.

Butyllithium-induced cyclotrimerisation reactions of organic nitriles: solvent dependency, crystal and solution structures of lithio triazine intermediates and an unexpected rearrangement of dihydrotriazino anions

Sequential addition of ButCN and PhCN (2 equiv.) to BunLi in the presence of tetrahydrofuran (THF) produces an isolable lithio 1,4 dihydrotriazine tris(THF) solvate, characterized by both NMR spectroscopic X-ray crystallographic methods, which converts to a 1,2-dihydro arrangement on methanolysis.