INDISCRIMINATE REACTION OF METHYLENE WITH THE CARBON-HYDROGEN BOND

Trifluoroethylation and Pentafluoropropylation of C(sp3)-H Bonds

Polyfluorinated substituents often enhance effectiveness, improve the stability within metabolic processes, and boost the lipophilicity of biologically active compounds. However, methods for their introduction into aliphatic carbon chains remain very limited. A potentially general route to integrate the fluorinated scaffolds into organic molecules involves insertion of fluorine-containing carbenes into C(sp3)-H bonds. The electron-withdrawing characteristics of perfluoroalkyl groups enhances the reactivity of these carbenes which should enable the functionalization of unactivated C(sp3)-H bonds. Curiously, it appears that use of perfluoroalkyl-containing carbenes in alkane C-H functionalization is exceedingly rare. This concept describes photolysis, enzymatic catalysis, and transition metal catalysis as three primary approaches to C(sp3)-H functionalization by trifluoromethylcarbene and its homologues.

Hydrogen Bonding Shuts Down Tunneling in Hydroxycarbenes: A Gas-Phase Study by Tandem-Mass Spectrometry, Infrared Ion Spectroscopy, and Theory

Hydroxycarbenes can be generated and structurally characterized in the gas phase by collision-induced decarboxylation of α-keto carboxylic acids, followed by infrared ion spectroscopy. Using this approach, we have shown earlier that quantum-mechanical hydrogen tunneling (QMHT) accounts for the isomerization of a charge-tagged phenylhydroxycarbene to the corresponding aldehyde in the gas phase and above room temperature. Herein, we report the results of our current study on aliphatic trialkylammonio-tagged systems. Quite unexpectedly, the flexible 3-(trimethylammonio)propylhydroxycarbene turned out to be stable─no H-shift to either aldehyde or enol occurred. As supported by density functional theory calculations, this novel QMHT inhibition is due to intramolecular H-bonding of a mildly acidic α-ammonio C-H bonds to the hydroxyl carbene's C-atom (C:···H-C). To further support this hypothesis, (4-quinuclidinyl)hydroxycarbenes were synthesized, whose rigid structure prevents this intramolecular H-bonding. The latter hydroxycarbenes underwent "regular" QMHT to the aldehyde at rates comparable to, e.g., methylhydroxycarbene studied by Schreiner et al. While QMHT has been shown for a number of biological H-shift processes, its inhibition by H-bonding disclosed here may serve for the stabilization of highly reactive intermediates such as carbenes, even as a mechanism for biasing intrinsic selectivity patterns.

Ultrafast Photoelimination of Nitrogen from Upper Excited States of Diazoalkanes and the Fate of Carbenes Formed in the Reaction

The photochemical reactivity of diphenyldiazomethane 1 and phenyl 1- and 2-adamantyl diazomethanes 2 and 3, respectively, was investigated by transient absorption spectroscopy (TA). Photoelimination of N₂ upon UV excitation takes place in the anti-Kasha ultrafast photochemical reaction from the upper excited singlet states to deliver singlet carbenes, which were, in the case of 1 and 2, detected by fs-TA. The reactivity of the carbenes differs with respect to the substituent at the carbene center. The singlet car-1 in a nonpolar solvent delivers the triplet carbene by intersystem crossing (ISC). Singlet car-2 does not undergo ISC but reacts in the intermolecular insertion reactions into C-H bonds. Car-3 has an α-C-H bond next to the carbene center and reacts rapidly in the intramolecular C-H insertion reaction to deliver alkene, precluding its detection by fs-TA. However, the isolation of ketone photoproducts from 3 is highly indicative of triplet car-3's intermediate formation. The TA spectra from the S₁-S₃ states of 1-3 were computed using time-dependent density functional theory, while the multiconfigurational perturbation theory to the second order was used for the absorption spectra of the corresponding singlet and triplet carbenes. The modeled and measured spectra are in good agreement, and the computations corroborate the assignments of the key short-lived intermediates.

Visible-light-induced organocatalytic enantioselective N-H insertion of α-diazoesters enabled by indirect free carbene capture

While asymmetric insertion of metal carbenes into H-X (X = C, N, O, etc.) bonds has been well-established, asymmetric control over free carbenes is challenging due to the presence of strong background reactions and lack of any anchor for a catalyst interaction. Here we have achieved the first photo-induced metal-free asymmetric H-X bond insertion of this type. With visible light used as a promoter and a chiral phosphoric acid used as a catalyst, α-diazoesters and aryl amines underwent smooth N-H bond insertion to form enantioenriched α-aminoesters with high efficiency and good enantioselectivity under mild conditions. Key to the success was the use of DMSO as an additive, which served to rapidly capture the highly reactive free carbene intermediate to form a domesticated sulfoxonium ylide.

High-resolution infrared spectroscopy of supersonically cooled singlet carbenes: Bromomethylene (HCBr) in the CH stretch region

First high-resolution spectra of cold (∼35 K) singlet bromomethylene HCBr in the CH stretching (v₁) region from 2770 to 2850 cm^-1 are reported using near quantum shot-noise limited laser absorption methods in a slit jet supersonic discharge expansion source. Three rovibrational bands are identified at high S/N (20:1-40:1) and rotationally assigned to (i) the CH stretch fundamental (v₁) band X̃1,0,0←X̃0,0,0 and (ii) vibrational hot bands [X̃(1,1,0)←X̃(0,1,0) and X̃(1,0,1)←X̃(0,0,1)] arising from vibrationally excited HCBr populated in the discharge with single quanta in either the H-C-Br bend (v₂) or C-Br stretch (v₃) modes. Precision rotational constants are reported for a total of six states, with an experimentally determined CH stretch vibrational frequency (2799.38 cm^-1) in good agreement with previous low-resolution fluorescence studies [M. Deselnicu et al., J. Chem. Phys. 124(13), 134302 (2006)]. Detailed analysis of the fundamental v₁ band highlights the presence of perturbations in the X̃1,0,0 level, which we tentatively attribute to arise from the nearby triplet state ã(0,0,1) through spin-orbit interaction or the multiple quanta X̃0,2,1 singlet state via c-type Coriolis coupling. Reduced-Doppler resolution (60 MHz) in the slit-jet IR spectrometer permits for clear observation of a nuclear spin hyperfine structure, with experimental line shapes well reproduced by nuclear quadrupole/spin-rotation coupling constants from microwave studies [C. Duan et al., J. Mol. Spectrosc. 220(1), 113-121 (2003)]. Finally, the a-type to b-type transition intensity ratio for the fundamental CH stretch band is notably larger than that predicted by using a bond-dipole model, which from high level ab initio quantum calculations [CCSD(T)/PVQZ] can be attributed to vibrationally induced "charge-sloshing" of electron density along the polar C-Br bond.

σ0π2 Singlet Ground State Carbenes Undergo Least-Motion Reactions with H2 and Alkenes

Ground state singlet carbenes commonly feature σ²π⁰ orbital occupations and are known for their concerted σ-bond insertion and cycloaddition reactions. Despite the facility of these transformations, orbital symmetry conservation forces them into non-least-motion π-approach reaction pathways. This situation completely changes when the singlet σ⁰π² electron configuration becomes the ground state, which we show here by means of high-level CCSD(T) geometry optimizations. Carbenes like the experimentally known 2H-imidazol-2-ylidene react with H₂ and ethylene with negligible or no barrier in a σ-fashion, which effectively corresponds to a least-motion reaction trajectory.

Transition-metal-carbene-like intermolecular insertion of a borylene into C-H bonds

We demonstrate that, in analogy to transition-metal carbene chemistry, [(OC)5Mo[double bond, length as m-dash]BN(SiMe3)2] facilitates intermolecular transfer of the borylene [:BN(SiMe3)2], which ultimately undergoes insertion into C-H bonds under very mild conditions. The one-pot multiple functionalization of the cyclopentadienyl rings of tungstenocene dihydride is demonstrated using this approach.

Correlation between Labeling Yield and Surface Accessibility in Covalent Labeling Mass Spectrometry

The functional properties of a protein are strongly influenced by its topography, or the solvent-facing contour map of its surface. Together with crosslinking, covalent labeling mass spectrometry (CL-MS) has the potential to contribute topographical data through the measurement of surface accessibility. However, recent efforts to correlate measures of surface accessibility with labeling yield have been met with mixed success. Most applications of CL-MS involve differential analysis of protein interactions (i.e., footprinting experiments) where such inconsistencies have limited effect. Extending CL-MS into structural analysis requires an improved evaluation of the relationship between labeling and surface exposure. In this study, we applied recently developed diazirine reagents to obtain deep coverage of the large motor domain of Eg5 (a mitotic kinesin), and together with computational methods we correlated labeling yields with accessibility data in a number of ways. We observe that correlations can indeed be seen at a local structural level, but these correlations do not extend across the structure. The lack of correlation arises from the influence of protein dynamics and chemical composition on reagent partitioning and, thus, also on labeling yield. We conclude that our use of CL-MS data should be considered in light of "chemical accessibility" rather than "solvent accessibility" and suggest that CL-MS data would be a useful tool in the fundamental study of protein-solute interactions.

Photoelimination of nitrogen from adamantane and pentacycloundecane (PCU) diazirines: a spectroscopic study and supramolecular control

Photochemical reactivity of pentacycloundecane (PCU) and adamantane diazirines was investigated by preparative irradiation in different solvents, laser flash photolysis (LFP) and quantum chemical computations. In addition, formation of inclusion complexes for diazirines with cucurbit[7]uril, β- and γ-cyclodextrin (β- and γ-CD) was investigated by 1H NMR spectroscopy, isothermal microcalorimetry and circular dichroism spectroscopy, followed by the investigation of photochemical reactivity of the formed complexes. Diazirines undergo efficient photochemical elimination of nitrogen (ΦR > 0.5) and deliver the corresponding singlet carbenes. Singlet carbenes react in intra- and intermolecular reactions and we found a rare singlet carbene pathway in CH3OH involving protonation and formation of a carbocation, detected due to the specific rearrangement of the pentacycloundecane skeleton. Singlet diazirines undergo intersystem crossing and deliver triplet carbenes that react with oxygen to form ketones which were isolated after irradiation. Our main finding is that the formation of diazirine inclusion complexes with β-CD and γ-CD changes the relative ratio of singlet vs. triplet pathways, with singlet carbene products being dominant from the chemistry of the irradiated complexes. Our combined theoretical and experimental studies provide new insights into the supramolecular control of carbene reactivity which has possible applications for the control of product distribution by solvent effects and the choice of constrained media.

Infrared spectroscopy of jet-cooled HCCl singlet chlorocarbene diradical: CH stretching and vibrational coupling dynamics

Quantum shot noise limited laser absorption methods are used to obtain first high-resolution infrared rovibrational spectra of jet cooled chlorocarbene (HCCl) diradical in a supersonic slit-jet discharge expansion spectrometer. The rotationally resolved absorption spectra of the C-H stretch ν₁ fundamental are analyzed in the framework of a Watson non-rigid asymmetric rotor Hamiltonian model. Further analysis of the mid-infrared data reveals the additional presence of what has nominally been assigned as the X̃(012) combination band with one quantum of the H-C-Cl bend (ν₂) and two quanta of the C-Cl stretch (2ν₃). Rovibrational constants are obtained from least squares fits for each of the four excited vibrational states built on the ν₁ fundamental X̃(100) and the X̃(012) combination mode for each ³⁵Cl and ³⁷Cl atom isotopologue. The four bands occur within a narrow spectral window, requiring detailed comparison of multiple spectral properties (e.g., rotational constant dependence on vibrational excitation, band types/transition dipole moment alignment in the body-fixed frame, etc.) to aid in the vibrational assignment. Indeed, the IR transition intensities arise from strong anharmonic mixing between the "bright" ν₁ C-H stretch and "dark" X̃012 H-C-Cl bend/C-Cl stretch combination modes, resulting in nearly equal amplitudes for the zeroth order X̃(100) and X̃012 harmonic states. Finally, to aid the spectral search for HCCl in the interstellar medium, ground state two-line combination differences are combined with previous laser-induced fluorescence results to predict precision microwave transitions for HC³⁵Cl and HC³⁷Cl.

Rhodium(II)-catalysed intramolecular C-H insertion α- to oxygen: reactivity, selectivity and applications to natural product synthesis

The selective functionalisation of C-H bonds is a powerful strategy for the construction of organic molecules and the Rh(II)-catalysed C-H insertion reaction is a particularly robust and useful tool for this purpose. This review discusses the insertion of Rh(II) carbenes into C-H bonds that are activated by α-oxygen substituents, focusing on the trends that have been observed in reactivity and selectivity, and the applications of this reaction to the total synthesis of complex natural products.

A perspective on physical organic chemistry

A perspective on the development of mechanistic carbene chemistry is presented. The author will point out questions that have been answered, and a next generation of questions will be proposed.

A comparative study of ATP analogs for phosphorylation-dependent kinase-substrate crosslinking

Kinase-catalyzed protein phosphorylation is an important post-translational modification that regulates a variety of cellular functions. Identification of the many substrates of a specific kinase is critical to fully characterize cell biology. Unfortunately, kinase-substrate interactions are often transient, which makes their identification challenging. Here, the transient kinase-substrate complex was stabilized by covalent crosslinking using γ-phosphate modified ATP analogs. Building upon prior use of an ATP-aryl azide photocrosslinking analog, we report here the creation of an ATP-benzophenone photocrosslinking analog. ATP-benzophenone displayed a higher conversion percentage but more diffuse crosslinking compared to the ATP-aryl azide analog. A docking study was also performed to rationalize the conversion and crosslinking data. In total, the photocrosslinking ATP analogs produced stable kinase-substrate complexes that are suitable for future applications characterizing cell signaling pathways.

Borylnitrenes: electrophilic reactive intermediates with high reactivity towards C-H bonds

Borylnitrenes (catBN 3a and pinBN 3b; cat = catecholato, pin = pinacolato) are reactive intermediates that show high tendency towards insertion into the C-H bonds of unactivated hydrocarbons. The present article summarizes the matrix isolation investigations that were aimed at identifying, characterizing and investigating the chemical behaviour of 3a by spectroscopic means, and of the experiments in solution and in the gas phase that were performed with 3b. Comparison with the reactivity reported for difluorovinylidene 1a in solid argon indicates that 3a shows by and large similar reactivity, but only after photochemical excitation. The derivative 3b inserts into the C-H bonds of hydrocarbon solvents in high yields and thus allows the formation of primary amines, secondary amines, or amides from "unreactive" hydrocarbons. It can also be used for generation of methylamine or methylamide from methane in the gas phase at room temperature. Remaining challenges in the chemistry of borylnitrenes are briefly summarized.

William von Eggers Doering's many research achievements during the first 65 years of his career in chemistry

This Account highlights William von Eggers Doering's important discoveries in many fields of chemistry. His synthetic and mechanistic studies have contributed to areas including non-benzenoid aromatics, carbenes, pericyclic reactions, and diradical intermediates. Doering's synthesis with L. H. Knox of the highly stable tropylium ion and their investigation of its reactivity were the starting point for the development of the field of non-benzenoid aromatics. Working with A. K. Hoffmann, Doering demonstrated the synthesis of dichloro- and dibromocarbene by base-induced alpha elimination of HCl or HBr from CHCl3 or CHBr3 under anhydrous conditions. These results allowed for the synthesis of a variety of cyclopropanes and derivatives including allenes. Using 14C labeling experiments, Doering and Prinzbach showed that the mechanism of insertion of singlet methylene into a C-H bond was a concerted process.In their work on the Cope rearrangement, Doering and Roth's outstanding stereochemical analysis showed that the rearrangement of acyclic 1,5-hexadienes proceeds concertedly, passing over a chairlike transition state. This work has had an enormous impact on the understanding of stereochemical control in synthetic organic chemistry, and many fruitful applications in synthesis have stemmed directly from this finding. Transition-state resonance structures analogous to those for ground-state aromatics can qualitatively explain the relatively large substituent effects on the rate of the Cope rearrangement. However, quantum chemical calculations have quantitatively described these effects. The rapid degenerate Cope rearrangements in the cis-divinylcyclopropane units of 3,4-homotropilidene, barbaralone, and bullvalene establish these molecules as having fluxional structures. The unique molecule bullvalene has more than 1.2 million possible structures interconnected by degenerate Cope rearrangements, which average all H and all C atoms. Doering has also examined stepwise thermal reorganizations that pass through intermediary 1,3- or 1,4-diradicals and do not show conformational equilibration as would be expected for classical intermediates. Doering calls these processes "not-obviously concerted". He discusses "continuous diradicals" as transition states and rationalizes the course of these reactions through the concept of a "caldera" (a flat surface with small energy wells as found on the top of volcanoes).The understanding of fundamental chemical reactions remains the focus of Doering's research. In his terms, "understanding" means not only gaining deep insight but also the intellectual control that allows researchers to predict a reaction's course. Because the interplay between theory and experiment has led to great progress in this predictive ability, Doering's experimental work has provided an important input for computational chemistry and to the essential understanding of chemical reactions.

Synthesis and reactivity of nonstabilized diazo sugars

1,6-Anhydro-4-deoxy-4-diazo-2,3-O-isopropylidene-beta-D-lyxo-hexopyranose (4) is a stable crystalline compound readily accessible by an improved synthetic procedure. It has been used as a model for evaluating the reactivity of the diazo group, when not stabilized by an adjacent carbonyl function, in a rigid chiral matrix. A range of carbene-type, electrophile-promoted, and 1,3-dipolar reactions were evaluated, leading to 4,4'-alkene dimers, 4-deoxy-3-enose and related derivatives, 4,4-dihalo compounds, 4-spirocyclopropane derivatives, 4-spiropyrazole structures, and by skeletal rearrangement, branched-chain anhydropentose structures having a bicyclo[2.2.2] skeleton.

Hydrogen for Fluorine Exchange in CH4-xFx by Monomeric [1,2,4-(Me3C)3C5H2]2CeH: Experimental and Computational Studies

The monomeric metallocenecerium hydride, Cp'(2)CeH (Cp' = 1,2,4-tri-tert-butylcyclopentadienyl), reacts instantaneously with CH(3)F, but slower with CH(2)F(2), to give Cp'(2)CeF and CH(4) in each case, a net H for F exchange reaction. The hydride reacts very slowly with CHF(3), and not at all with CF(4), to give Cp'(2)CeF, H(2), and 1,2,4- and 1,3,5-tri-tert-butylbenzene. The substituted benzenes are postulated to result from trapping of a fluorocarbene fragment derived by alpha-fluoride abstraction from Cp'(2)CeCF(3). The fluoroalkyl, Cp'(2)CeCF(3), is generated by reaction of Cp'(2)CeH and Me(3)SiCF(3) or by reaction of the metallacycle, [(Cp')(Me(3)C)(2)C(5)H(2)C(Me(2))CH(2)]Ce, with CHF(3), and its existence is inferred from the products of decomposition, which are Cp'(2)CeF, the isomeric tri-tert-butylbenzenes and in the case of Me(3)SiCF(3), Me(3)SiH. The fluoroalkyls, Cp'(2)CeCH(2)F and Cp'(2)CeCHF(2), generated from the metallacycle and CH(3)F and CH(2)F(2), respectively, are also inferred by their decomposition products, which are Cp'(2)CeF, CH(2), and CHF, respectively, which are trapped. DFT(B3PW91) calculations have been carried out to examine several reaction paths that involve CH and CF bond activation. The calculations show that the CH activation by Cp(2)CeH proceeds with a low barrier. The carbene ejection and trapping by H(2) is the rate-determining step, and the barrier parallels that found for reaction of H(2) with CH(2), CHF, and CF(2). The barrier of the rate-determining step is raised as the number of fluorines increases, while that of the CH activation path is lowered as the number of fluorines increases, which parallels the acidity.

A Computational Investigation of the Reactions of Methylene, Chlorocarbene, and Dichlorocarbene with Cyclopropane

The reactions of CH(2), CHCl, and CCl(2) with cyclopropane, 1, have been examined computationally. In all cases the lowest energy reaction between the carbene and 1 is predicted to be C-H insertion. In the reaction of CH(2) with 1, the transition state for C-C insertion leading to cyclobutane is 1.7 kcal/mol higher in enthalpy than the transition state for C-H insertion at the G3B3 level. A pathway higher in energy than C-H insertion in the reactions of CHCl and CCl(2) with 1 involves two-bond cleavages generating ethylene along with chloro and dichloroethylene, respectively.

Probing protein conformation with a minimal photochemical reagent

3H-diazirine (3H-DZN), a photoreactive gas similar in size to water, was used to probe the topography of the surface and inner space of proteins. On photolysis 3H-DZN generates 3H-methylene carbene, which reacts unselectively with its molecular cage, inserting even into C-H bonds. Labeling of bovine alpha-lactalbumin (alpha-LA, MW: 14,200) with 1 mM (3)H-DZN yielded 0.0041 mol CH2/mol of protein, in agreement with the expectation for an unspecific surface-labeling phenomenon. The cooperative urea-induced unfolding of alpha-LA, as monitored by the extent of 3H-methylene labeling, agrees with that measured by circular dichroism spectroscopy in the far and near ultraviolet regions. At 8 M urea, the unfolded state U was labeled 25-30% more than the native state N primarily because of the increase in the accessible surface area (ASA) of the protein occurring upon unfolding. However, this result lies below the approximately 100% increment expected from theoretical estimates of ASA of state U. Among other factors, most likely the existence of a residual structure in U, that involves helices H2 and H4 of the alpha subdomain, might account for this fact, as shown by a comparative analysis of peptide labeling patterns of N and U samples. In this paper, we demonstrate the usefulness of the 3H-methylene labeling method to monitor conformational transitions and map solvent accessibility along the polypeptide sequence, thus opening the possibility of outlining structural features of nonnative states (i.e., denatured states, molten globule). We anticipate that this technique also would help to identify ligand binding and oligomerization sites in proteins.

Methylene as a possible universal footprinting reagent that will include hydrophobic surface areas: overview and feasibility: properties of diazirine as a precursor

Methylene is one of, if not the, most reactive organic chemical known. It has a very low specificity, which makes it essentially useless for synthesis, but suggests a possible role in protein footprinting with special importance in labeling solvent accessible nonpolar areas, identifying ligand binding sites, and outlining interaction areas on protomers that form homo or hetero oligomers in cellular assemblies. The singlet species is easily and conveniently formed by photolysis of diazirine. The reactions of interest are insertion into C-H bonds and addition to multiple bonds, both forming strong covalent bonds and stable compounds. Reaction with proteins and peptides is reported even in aqueous solutions where the vast majority of the reagent is used up in forming methanol. Species containing up to 5 to 10 extra :CH2 groups are easily detected by electrospray mass spectroscopy. In a mixture of a 14 Kd protein and a noninteracting 1.7 Kd peptide, the distribution of mass peaks in the electrospray spectra was close to that expected from random modification of the estimated solvent accessible area for the two molecules. For analysis at the single residue level, quantitation at labeling levels of one 13CH2 group per 10 to 20 kDa of protein appears to be possible with isotope ratio mass spectroscopy. In the absence of reactive solvents, photolysis of diazirine produces oily polymeric species that contain one or two nitrogen atoms, but not more, and are water soluble.

Effect of Angle Strain in Conjugated Cycloalkenylidenes. Singlet-Triplet Splitting of Cyclobutenylidene and Its Ground-State Intramolecular Rearrangements

The singlet and triplet states of cyclobutenylidene, cyclopenten-3-ylidene, cyclohexen-3-ylidene, and cyclohepten-3-ylidene and some of their isomers (cyclohexen-4-ylidene, cyclohepten-4-ylidene, and cyclohepten-5-ylidene) have been studied computationally (using ab initio and DFT methods) in order to assess the effect of angle strain on the S-T gap of small- and medium-size cyclic alkenylidenes. Ground-state intramolecular rearrangements of the conjugated cycloalkelnylidenes have also been examined with an emphasis on the smaller four-membered ring, which is compared to its higher homologues. It is found that cyclobutenylidene has a singlet ground state and a significant singlet-triplet gap (25 kcal mol(-)(1)). This strong preference for the singlet state may be understood if cyclobutenylidene is also viewed as bicyclobut-1(2)-ene. As the size of the ring increases, the singlet state becomes destabilized with respect to the triplet. The break-even point occurs with the six-membered ring where the triplet and singlet states are close in energy. The barrier for the 1,2 hydrogen shift in cyclobutenylidene (50.5 kcal mol(-)(1)) is found to be much higher compared to its higher homologues and to other alkylcarbenes. The ring contraction to form methylenecyclopropene (1,2 carbon shift) is energetically more favorable, requiring 34.8 kcal mol(-)(1). However, the lowest isomerization path available for singlet cyclobutenylidene is the formation of vinylacetylene, which is predicted to have a barrier of around 9 kcal mol(-)(1). This small but significant barrier implies that cyclobutenylidene should be observable.

Reactions of vibrationally excited molecules. I. The reaction of methylene with iso butene

The photolysis of diazomethane in the presence of iso butene has been investigated. The results obtained are explained on the basis that the methylene initially produced may be vibrationally excited, to an extent which depends on the wavelength of the radiation employed in the photolysis, and may also contain considerable kinetic energy. The methylene resets before this excess energy is lost, attacking the carbon hydrogen bonds and carbon carbon double bond in iso butene. The latter attack yields 1.1 -dimethyl cyclo Zopropane which contains sufficient energy to isomerize, and does so, unless stabilized by collision. The results obtained are compared with those published for the photolysis of keten in the presence of iso butene.