Photo-Fries rearrangement of 2-Naphthylbenzoate

Photo-Fries rearrangement of 2-Naphthylbenzoate gives 6-benzoyl-2-naphthol and 8-benzoyl-2-naphthol in addition to the expected product, 1-benzoyl-2-naphthol.     

Et2Zn-mediated rearrangement of bromohydrins

A simple and highly efficient method for the rearrangement of bromohydrins mediated by Et 2Zn to synthesize carbonyl compounds was described. Various beta-bromo alcohols were treated with 0.6 equiv of Et 2Zn to form a zinc complex in CH 2Cl 2 at room temperature for 2 h, followed by 1,2-migration to give the corresponding carbonyl compounds. This remarkable and clean rearrangement is general for acyclic and cyclic bromohydrins, and a variety of ring-expansive and -contractive carbonyl compounds were obtained in good to excellent yields according to the feature of the starting bromohydrins. The functional group tolerance of organozinc reagents in this reaction will be useful in organic synthesis. The scope and limitations of this rearrangement process were also investigated.     

PtCl2-catalyzed rearrangement of methylenecyclopropanes

Alkylidenecyclopropanes readily convert into cyclobutene derivatives on treatment with catalytic amounts of PtCl2. The reaction is strongly accelerated when performed under an atmosphere of CO (1 atm). The resulting cyclobutenes are isolated in good to excellent yields for substrates bearing aliphatic as well as aromatic substituents R on their olefinic site. If the substituent R, however, is a very electron-rich arene, the cyclobutenes initially formed react further to give dimeric products with a previously unknown 1,2,2a,7a-tetrahydrospiro[cyclobuta[a]indene-7,1'-cyclobutane skeleton. A mechanism accounting for these experimental observations as well as for a deuterium-labeling experiment is proposed which implies reactive intermediates at the nonclassical cation/carbene interface. Furthermore it is shown that the PtCl2-catalyzed cyclobutene formation can be geared with subsequent ring-opening/ring-closing metathesis (ROM/RCM) events. Finally, a convenient "one pot" method for the preparation of the alkylidenecyclopropane substrates used in this study is presented, which is based on a modified Julia-Kocienski olefination of aldehydes with readily available 1-tert-butyl-1H-tetrazol-5-yl-cyclopropyl sulfone under Barbier conditions.     

Thermal rearrangement of 2-bromooxazolines to 2-bromoisocyanates

A unprecedented thermally induced rearrangement of 2-bromo-4-substituted oxazolines into 2-bromoisocyanates with high selectivity has been observed. Isolated yields of 85-90% were obtained with 2-bromo-4-phenyloxazoline, 2-bromo-4-isopropyloxazoline, or 2-bromo-4,4-dimethyloxazoline. In addition, chiral aziridinecarboxamides or 2-aminooxazolines could be selectively obtained from the corresponding 2-bromo isocyanate depending on reaction conditions.     

The preparation and rearrangement of 2-allylbenzimidazole

This paper reports the preparation of 2-allylbenzimidazole (I) and the facile migration of its double bond to the known isomeric 2-propenylbenzimidazole (II). The proposed mechanisms of reactions of this type, involving a prototropic rearrangement, have been thoroughly discussed (1,2).     

Unusual thermal solid-phase rearrangement of 2-allylthio- and 2-allylselenodihydropyridines

A previously unreported thermal solid-phase migration of the allyl group was found for 2-allylthio- and 2-allylselenodihydropyridines, leading to 3-allyl-3-cyano-3,4-dihydropyridine-2(1H)-thiones and -selenones. Analysis of the crystal structures did not indicate whether the solid-phase reaction, which is probably general in nature, is intra- or intermolecular.Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No. 2, pp. 521–523, February, 1991.     

Synthesis and thermal rearrangement of allylic 3,5,6-trimethyl-2-pyrazinylacetates: A heterocyclic carroll rearrangement

The synthesis of allylic 3,5,6-trimethyl-2-pyrazinylacetates 2–4 has been achieved by the reaction of 3,5,6-trimethyl-2-pyrazinylacetic acid lithium salt ( 1 ) with phenyl dichlorophosphate followed by addition of the allylic alcohol. On thermolysis, the allylic β-heteroaromatic esters underwent a rearrangement, analogous to the Carroll rearrangement, to generate the corresponding γ,δ-unsaturated heteroaromatic compound. The configuration of the double bond formed in the product was the E-isomer. The rate of the rearrangement was dependent on the substitution pattern of the allylic portion of the molecule with 4>2>3 . The ester enolate version of the heterocyclic Carroll rearrangement was investigated with 2 , however these conditions did not promote the rearrangement.     

Synthesis of 2-methyl-D-erythritol via epoxy ester-orthoester rearrangement

The biomimetic epoxy ester[bond]orthoester rearrangement has been applied to a new synthesis of 2-methyl-D-erythritol, a branched five-carbon sugar of importance to the deoxyxylulose pathway of isoprenoid biosynthesis. The intermediate orthoacetate is one of the few [2.2.1]-orthoesters to have been reported. Labeling studies with O-18 indicated that this reaction proceeds exclusively via a 5-exo cyclization. NMR analysis of chiral esters indicated an ee of 87% for the starting epoxide and an ee of 86% for the product. This route represents a rapid and convenient method for the synthesis of 2-methyl-D-erythritol and is expected to be useful for generating isotopically labeled intermediates for biochemical studies.     

Degenerate rearrangement of 2H+-biphenylenonium ion

Conclusions The 2H⁺-biphenylenonium ion is formed when biphenylene is dissolved in the system HSO₃F-SbF₅-SO₂ClF, which undergoes degenerate rearrangement as the result of one of the hydrogen atoms of the CH₂ group shifting to the 3 position.Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No. 5, pp. 1199–1201, May, 1978.     

Fries rearrangement of methoxyphenyl 3-methylbut-2-enoates

Fries rearrangement of 2-, 3- and 4-methoxyphenyl 3-methylbut-2-enoates 3-5 in methanesulfonic acid, polyphosphoric acid, aluminum chloride and under photochemical conditions have been studied. The outcome of the reactions was determined by the substitution pattern in the starting products and the reaction conditions used. Under Lewis acid catalysis, acylation accounted for the major components of the reaction mixtures, leading to the formation of indanones and 2,3-dihydro-4H-1-benzopyran-4-ones respectively in the case of o- and m-esters 3 and 5 , whereas alkylation to afford dihydrocoumarins was the favored path for p-ester 5. On the other hand, o-acylation was in all cases the major reaction course in the photochemical rearrangement.     

Smiles rearrangement of polyfluoro substituted 2-acetylaminodiaryl ethers

Polyfluoro substituted 2-acetylaminodiaryl ethers of the type Ar_FOC₆H₄NHAc-o (II) that contain in the fluorinated ring an acceptor group, like analogs of the NH₂ group, undergo on heating in DMF the Smiles rearrangement accompanied by partial migration of the acetyl group and cyclization (in case of ethers (IIa, b)) to phenoxazine derivatives. In the case of heating in DMF, the rate constant of the rearrangement of diphenyl ether (IIa) is by an order of magnitude lower than the rate constant of the rearrangement of its analog with an NH₂ group.Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No. 4, pp. 850–854, April, 1990.     

Stereoselective oxidative rearrangement of 2-aryl tryptamine derivatives

The oxidation of 2-aryl tryptamines followed by a stereoselective rearrangement provides a versatile strategy for the synthesis of C3-quaternary oxindoles bearing a C3-aryl group. Treatment of optically active 2-aryl hydroxyindolenines with scandium trifluoromethanesulfonate in toluene at 110 degrees C leads to complete and stereoselective isomerization to the corresponding C3-aryl oxindoles which represent versatile intermediates for the synthesis of C3a-aryl hexahydropyrroloindoles.     

Lithium perchlorate-catalysed rearrangement of 1-methylcyclohex-2-enylhydroperoxide into 2-methylenecyclohexylhydroperoxide

The catalytic effect of 5 mol dm^?3 solution of LiClO₄ in Et₂O on the rearrangement of 1-methylcyclohex-2-enylhydroperoxide into 2-methylenecyclohexylhydroperoxide has been observed.     

Reinvestigation of the rearrangement of 2-acetylbenzofuran oxime tosylate

The acetal, resulting from the rearrangement of anti-2-acetylbenzofuran oxime tosylate (I) was proved to be a mixture of trans- (IX) and cis- (X) 2,3-dihydro-2-acetyl-2,3-dimethoxybenzofuran. The structure of these isomers as well as that of their oximes XI and XII was elucidated by ir, nmr, and mass spectral investigation and by the ir and nmr spectra of the benzoyl (XIII and XIV) and acetyl (XV and XVI) derivatives of the oximes. A new reaction mechanism concerning the rearrangement process is discussed.     

Syntheses of 2-arylated 1-benzazocines via Beckmann rearrangement

One-step and highly efficient syntheses of 2-aryl-1-benzazocines via Beckmann rearrangement of 5H-benzocyclohepten-5-one oxime mesylates in dry toluene was described, in which aryl Grignard reagents were used for the first time to induce Beckmann rearrangement directly without any additional protic agents. Iodotrimethylsilane was also employed to promote Beckmann rearrangement of the mesylates, followed by the treatment of the intermediate imidoyl iodide with phenylmagnesium bromide to complete the synthesis of benzazocines.     

Experimental and theoretical study of the 2-alkoxyethylidene rearrangement

The rearrangement of 2-ethoxyethylidene, generated photochemically from a nonnitrogenous precursor, leads to ethyl vinyl ether. Although this product could result, in principle, from a 1,2-hydrogen shift and/or a 1,2-ethoxy shift in the carbene, a deuterium labeling study indicates an essentially exclusive preference for hydrogen migration. The experimental results are in agreement with CCSD and W1BD calculations for the simpler 2-methoxyethylidene system that show a prohibitively large barrier for the methoxy shift and a negligible barrier for the hydride shift.