Isomerization methylene

The photolysis of the 4-alkylidene-l-pyrazoline (94) gives rise to two isomeric methylene cyclopropanes (95 and 96).76 The available evidence points to the intermediacy of a trimethylenemethyl species (97) in the triplet state which can cyclize in three ways. The same species is postulated in the photolysis of a series of 4-alkylidene-l-pyrazoline-3-carboxylates.77 This appears to be a general route to derivatives of trimethylenemethyl trimethylenemethyl itself has been generated from 4-methylene-1-pyrazoline and the triplet nature of the intermediate identified by electron spin resonance (ESR) spectroscopy.78... 

For example, irradiation of the Qo diazomethane adduct resulted in the formation of the [6,6]-closed cyclopropane QiHj, accompanied by the [5,6]-open fuUeroid. The two isomers cannot be converted neither photochemicaUy or therm ally.Upon photolysis and thermolysis of C70 pyrazolino derivatives 79a-c synthesized by addition of diazomethane to C70, four isomeric methylene derivatives of C70 are obtained. Irradiation of the pyrazolines leads to a mixture of the two isomeric [6,6]-bridged methano-fullerenes 81a and 81b, while the thermal reaction gives rise to the formation of the [5,6] -bridged isomers 80a and 80b (Scheme 35). ... 

Methoxy derivatives of divalent phenols such as guaiacol react like simple monovalent phenols, forming methylol and methylene derivatives. Euler and co-workers- isolated vanillyl alcohol (methjdolguaiacol) and a di-methylol derivative of a methylene-bis-methoxyphenol from the products obtained by reacting guaiacol with formaldehyde under alkaline conditions. Under acidic conditions tw o isomeric methylene-bis-methoxyphenols were obtained. 

Large annulenes tend to undergo conformational distortion, cis-trans isomerizations, and sig-matropic rearrangements (p. 40 and p. 100). Methylene-bridged conjugated (4n + 2)-ic cyclopolyenes were synthesized with the expectation that these almost planar annulenes should represent stable HOckel arenes (E, Vogel, 1970, 1975). 

Various terminal allylic compounds are converted into l-alkenes at room temperature[362]. Regioselective hydrogenolysis with formate is used for the formation of an exo-methylene group from cyclic allylic compounds by the formal anti thermodynamic isomerization of internal double bonds to the exocyclic position[380]. Selective conversion of myrtenyl formate (579) into /9-pinene is an example. The allylic sulfone 580 and the allylic nitro compound... 

As a further application of the reaction, the conversion of an endocyclic double bond to an c.xo-methylene is possible[382]. The epoxidation of an cWo-alkene followed by diethylaluminum amide-mediated isomerization affords the allylic alcohol 583 with an exo double bond[383]. The hydroxy group is eliminated selectively by Pd-catalyzed hydrogenolysis after converting it into allylic formate, yielding the c.ro-methylene compound 584. The conversion of carvone (585) into l,3-disiloxy-4-methylenecyclohexane (586) is an example[382]. 

Structures [VI] and [VII], respectively, are said to arise from head-to-tail or head-to-head orientations. In this terminology, the substituted carbon is defined to be the head of the molecule, and the methylene is the tail. Tail-to-tail linking is also possible. The term orienticity is also used to describe positional isomerism. 

DimeriZa.tlon. A special case of the [2 + 2] cyclo additions is the dimerization of ketenes. Of the six possible isomeric stmctures, only the 1,3-cyclobutanediones and the 2-oxetanones (P-lactones) are usually formed. Ketene itself gives predominandy (80—90%) the lactone dimer, 4-methylene-2-oxetanone (3), called diketene [674-82-8], approximately 5% is converted to the symmetrical dimer, 1,3-cyclobutanedione [15506-53-3] (4) which undergoes enol-acetylation to so-called triketene [38425-52-4] (5) (44). 

Furylfuramide. a[(5-Nitro-2-furaiiyl)-2-methylene]-2-furaiiacetamide, withdrawn from the market in Japan in 1974 because of mutagenicity, is prepared by condensation of 5-nitro-2-furancarboxaldehyde with 2-furanacetic acid followed by chlorination and amination (30). The isomerization of cis to trans form of fudyfuramide has been shown to occur in the presence of a variety of biological reducing agents (31). 

In the case of the 2-dimethylamino- (or 2-amino-)methylene derivatives, the products were at first thought to be pyrimido[4,5-c]isoquinolines (267), but later work with 6-(N-substituted amino)uracils assigned the structures of the products (268) as belonging to the isomeric pyrimido[4,5-f>]quinoline system (74CB2537), in agreement with the regioselection rules above. 

JA173) illustrates this possibility (Scheme 34). Thus 3,3,5-trimethyl-3//-pyrazole (371 R = H) on irradiation in pentane solution gives 1,3,3-trimethylcyclopropene (372 R = H) the intermediate diazoalkene (373) has been characterized. The tetramethyl derivative (371 R" = Me) when irradiated at -50 °C in methylene chloride leads to a species believed to be a l,2-dlazablcyclo[2.1.0]pent-2-ene (374). This isomerization is thermally reversible, the 3H- pyrazole being regenerated at room temperature. 

H-Azepine, 2-(o-hydroxyphenyl)-synthesis, 7, 538 3 H-Azepine, methyl- H NMR, 7, 495 3H-Azepine, 3-methylring inversion barrier, 7, 14 3 H-Azepine, 2-methylene-isomerization, 7, 505 3H-Azepine, 7-(N-phthalimido) synthesis, 7, 538 4H-Azepine, 4,5-dihydro-cyclization, 7, 524... 

Aziridine, 2,3-diphenyl-l-(2,4,6-trinitrophenyl)-irradiation, 7, 61 Aziridine, 1,2-divinyl-rearrangement, 7, 539 Aziridine, 2,3-divinyl-rearrangement, 7, 42, 65, 539 Aziridine, N-ethyl-inversion, 7, 6 Aziridine, 2-halo-reactions, 7, 74 Aziridine, A/-halo-invertomers, 7, 6 Aziridine, 2-methyl- N NMR, 7, 11 Aziridine, methylene-ring-ring valence isomerizations, 7, 22 synthesis, 7, 92 Aziridine, iV-nitroso-reactions, 7, 74 Aziridine, iV-phosphino-inversion, 7, 7 Aziridine, 1-phthalimido-UV irradiation, 7, 62-63 Aziridine, l-(3-thienyl)-2-vinyl-rearrangement, 4, 746 Aziridine, 7V-trimethylsilyl-inversion, 7, 7 Aziridine, 1,2,3-triphenyl-irradiation, 7, 61 Aziridine, vinyl-isomerization, S, 287 Aziridinecarboxylic acid ring expansion, 7, 262 Aziridine-2,2-dicarboxylic acid, 1-methoxy-diethyl ester... 

Oxazol-5(2H)-one, 2-benzylidene-4-methyl-tautomerism, 6, 186 Oxazol-5(2ff)-one, 2-methylene-isomerization, 6, 226 Oxazol-5(2H)-one, 2-trifluoromethyl-acylation, 6, 201 Oxazol-5(4ff)-one, 4-allyl-thermal rearrangements, 6, 199 Oxazol-5(4H)-one, 4(arylmethylene)-Friedel-Crafts reactions, 6, 205 geometrical isomerism, 6, 185 Oxazol-5(4ff)-one, 4-benzylidene-2-phenyl-configuration, 6, 185 photorearrangement, 6, 201 Oxazol-5(4ff)-one, 4-benzyl-2-methyl-Friedel-Crafts reactions, 6, 205 Oxazol-5(4ff)-one, 4-methylene-in amino acid synthesis, 6, 203 Oxazol-5(4ff) -one. 2-trifluoromethyl-hydrolysis, 6, 206 Oxazolones... 

In the 19-nor series, the reaction with NOF is more complex and there is isolated in addition to the fluoro nitrimine corresponding to (31) a 20% yield of the nitroso dimer (34), which dissolves in methanol-methylene dichloride solution to give the pure blue color characteristic of the monomer (35). The latter then isomerizes to the oxime (36). 

Oxidation of the hydroxy group in (10) to the ketone followed by isomerization affords the 10oc-methyl-A -3-ketone (11). In contrast, methylenation of 3)5-hydroxy-A ° -compounds proceeds in refluxing ether solution to give, after oxidation and acid rearrangement, the natural 10/5-methyl-A -3-keto steroids. With an epimeric mixture of 3fi- and 3a-A ° -alcohols only the )5-alcohol reacts under these imild conditions. ... 

FIGURE 4.20 The bond dissociation energies of methylene and methyl C—H bonds in propane reveal difference in stabilities between two isomeric free radicals. The secondary radical is more stable than the primary. 

The Nenitzescu process is presumed to involve an internal oxidation-reduction sequence. Since electron transfer processes, characterized by deep burgundy colored reaction mixtures, may be an important mechanistic aspect, the outcome should be sensitive to the reaction medium. Many solvents have been employed in the Nenitzescu reaction including acetone, methanol, ethanol, benzene, methylene chloride, chloroform, and ethylene chloride however, acetic acid and nitromethane are the most effective solvents for the process. The utility of acetic acid is likely the result of its ability to isomerize the olefinic intermediate (9) to the isomeric (10) capable of providing 5-hydroxyindole derivatives. The reaction of benzoquinone 4 with ethyl 3-aminocinnamate 35 illustrates this effect. ... 

On carbonylation in methylene chloride it undergoes the substitution of the diene ligands, rearrangement, and cis-trans isomerization to yield 64 (97JOM(530) 259). l,r-(l,2-Ethylene)-3,3 -imidazol-2,2 -diylidene and the dimer [(T -cod)Rh (ir-Cl)] form the dinuclear species 65. 

Subsequently, it was shown that ring expansion of these bicyclic systems is followed by a series of proton shifts involving the isomeric 2- and 5-methyleneazepines. The former were detected spectroscopically ( H NMR) whereas, in some cases, the latter were isolated.127 For example, 4,6-dimethyl-2-methylene-3-phenyl-3-azabicyclo[4.1,0]hept-4-ene-l, 5-dicarbonitrile (28), on treatment with hydrochloric acid in chloroform, yields the 4-methyleneazepine 29, which on prolonged heating with acid is converted into the 1//-azepine 30. 

Addition of benzoyl chloride to 2.5-dimethyl-3,4,6-triphenyl-3//-azepine (13) in benzene in the presence of 1,8-diazabicyclo[5.4.0]undec-7-ene (DBU) leads to elimination of hydrogen chloride and formation of the 2-methylene-l//-azcpine 14.117 All attempts to isomerize the methylene derivative to 1-benzoyl-2,5-dimethyl-3,4,6-triphenyl-l//-azepine under basic conditions failed. Analogous reactions can occur with 2,5-dielhyl-3,4,6-triphenyl-3//-azepine. 

In contrast, the diphenyl derivative 44 (R1 = R2 = Ph) fails to ring expand, whereas the methyl derivative 44 (R1 = Me R2 = H) yields the a.xo-methylene compound 45 (63 %), which undergoes quantitative acid-catalyzed isomerization to 10-methyl-5/7-dibenz[6,/]azepine (46) in refluxing toluene. The mechanistic implications of these reactions have been discussed. 

Intramolecular allylzinc aldehyde additions lead, in one synthetic step, to bicyelic a-methylene-y-lactones41. Interestingly, the (Z)-isomer gave only the r/5-fused bicyclic products, which arises from a. vyw-selectivc addition, while the ( >isomeric bromide furnished a cisjtrans mixture (yield 56%, cisjtrans 72 28)41 indicating that the double-bond torsion and the intramolecular carbonyl addition have similar rates. A similar sequence was the key step in a confertin synthesis28. 

MEDINA in an acronym for MEthylene DINtrA-mine. In earlier literature it was called MEDNA (Ref 2), the latter name later used for the isomeric compd me thylenedi-isonitramine which was obtained by the action of nitric oxide on acet (Beil 1, 592) (See under MEDNA in this... 

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