- Fragmentation of cyclobutoxychlorocarbene: The cyclopropylcarbinyl/cyclobutyl cations revisited
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Fragmentations of cyclobutoxychlorocarbene (13, kfrag= 7.1 × 105 s-1) and cyclopropylmethoxychlorocarbene (14, kfrag = 7.6 × 105 s-1) in MeCN proceed to tight and distinct [R+ OC Cl-] ion pairs, which collapse to different distributions of cyclopropylcarbinyl, cyclobutyl and allylcarbinyl chlorides. B3LYP/6-31G* calculations support these conclusions, affording computed fragmentation activation energies of 6.4 (13) and 3.0 (14) kcal mol-1.
- Moss, Robert A.,Zheng, Fengmei,Johnson, Lauren A.,Sauers, Ronald R.
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- Rearrangement, nucleophilic substitution, and halogen switch reactions of alkyl halides over NaY zeolite: Formation of the bicyclobutonium cation inside the zeolite cavity
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Rearrangement and nucleophilic substitution of cyclopropylcarbinyl bromide over NaY and NaY impregnated with NaCl was observed at room temperature. The first-order kinetics are consistent with ionization to the bicyclobutonium cation, followed by internal return of the bromide anion or nucleophilic attack by impregnated NaCl to form cyclopropylcarbinyl, cyclobutyl, and allylcarbinyl chlorides. The product distribution analysis revealed that neither a purely kinetic distribution, similar to what is found in solution, nor the thermodynamic ratio, which favors the allylcarbinyl halide, was observed. Calculations showed that bicyclobutonium and cyclopropylcarbinyl carbocations are minimal over the zeolite structure, and stabilized by hydrogen bonding with the framework structure. A new process of nucleophilic substitution is reported, namely halogen switch, involving alkyl chlorides and bromides of different structures. The reaction occurs inside the zeolite pores, due to the confinement effects and is an additional proof of carbocation formation on zeolites. The results support the idea that zeolites act as solid solvents, permitting ionization and solvation of ionic species.
- Franco, Marcelo,Rosenbach Jr., Nilton,Ferreira, Glaucio B.,Guerra, Antonio C. O.,Kover, W. Bruce,Turci, Cassia C.,Mota, Claudio J. A.
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- Rearrangements concerted with fragmentation of cyclopropylmethoxychlorocarbene and cyclobutoxychlorocarbene in hydrocarbon solvents and Ar matrices
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Fragmentations of cyclopropylmethoxychlorocarbene (6) and cyclobutoxychlorocarbene (10) lead to rearrangments that afford mixtures of cyclopropylmethyl chloride (7), cyclobutyl chloride (8), and 3-butenyl chloride (9). Isotopic substitution studies show that these rearrangments are accompanied by partial exchange of the methylene groups within 6 and 10. Surprisingly, these processes that are typical of carbocations persist in hydrocarbon solvents such as pentane and cyclohexane-d12. Quantum chemical calculations reveal that the cis-conformers of the incipient oxychlorocarbenes C 4H7OCCl decay to C4H7Cl + CO via transient hydrogen bonded C4H7 σ+...Clσ- complexes which possess significant ion pair character, even in the gas phase or in nonpolar solvents. In contrast to benzyloxychlorocarbene, no free radicals are formed upon generation or photolysis of 6 or 10 in Ar matrixes, although acid chlorides (the recombination products of these radical pairs) are observed. The IR spectra obtained in these experiments show the presence of several conformers of the two C4H7OCCl.
- Moss, Robert A.,Sauers, Ronald R.,Zheng, Fengmei,Fu, Xiaolin,Bally, Thomas,Maltsev, Alexander
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- Fragmentation of alkoxychlorocarbenes in the gas phase
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In contrast to photolysis or thermal decomposition in solution, which is dominated by ionic reactions, flash vacuum pyrolysis of alkylchlorodiazirines in the gas phase generates radicals. The cyclopropylcarbinyl system is re-examined and the l-norbornylca
- Blake, Michael E,Jones Jr., Maitland,Zheng, Fengmei,Moss, Robert A
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p. 3069 - 3071
(2007/10/03)
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- A Convenient Large-Scale Synthesis of Cyclobutyl Halides
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An improved method for the preparation of multigram quantities of cyclobutyl halides is described.The Grignard reactivity of these halides is also discussed.
- Dupont, Andrea C.,Audia, Vicki H.,Waid, Philip P.,Carter, J. Paul
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p. 1011 - 1021
(2007/10/02)
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- FRAGMENTATION OF CYCLOPROPYLMETHOXYCHLOROCARBENE: FORMATION OF CYCLOPROPYLCARBINYL/CHLORIDE ION PAIRS
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The decomposition of cyclopropylmethyloxychlorodiazirine in MeCN proceeds via N2 and CO loss, mainly to tight cyclopropylcarbinyl cation-chloride anion pairs that collapse to C4 chlorides with substantial skeletal and label retention; the ion pairs can be intercepted by ethanol with less skeletal retention.
- Moss, Robert A.,Ho, Guo Jie,Wilk, Bogdan K.
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p. 2473 - 2476
(2007/10/02)
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- ON THE REACTION OF ALCOHOLS WITH HALOCARBENES. ARE CARBOCATIONS INTERMEDIATES?
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There is no evidence for hydride shift in the reaction of alcohols 1 and 2 with dichlorocarbene.Accordingly, the intermediate cannot be a free carbocation.It is suggested that the products are formed through a combination of SNi and direct displacement reactions in which tight ion pairs are involved.
- Likhotvorik, Igor R.,Jones, Maitland,Yurchenko, Alexander G.,Krasutsky, Pavel A.
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p. 5089 - 5092
(2007/10/02)
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- PREPARATION OF SOME ALKYL CHLORIDES BY DECOMPOSITION OF ALKOXYPHOSPHONIUM CHLORIDES AND BICHLORIDES
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A number of alkoxyphosphonium chlorides and bichlorides have been prepared as stable intermediates or transient species.The thermal decompositions of these salts have been studied under a variety of conditions.The salts decompose by SN2 and SN1 processes in a fairly predictable manner.There are two decided advantages to using these salts as precursors to alkyl halides.The first is that in systems that are normally prone to rearrangements under substitution conditions, the products of decompositions of the salts are often formed with less rearrangement than is often found in other systems.The second is that the phosphates and phosphine oxides are excellent leaving groups and thus substitutions can be effected at centers that normally react very slowly.
- Denney, Donald B.,Garth, Bruce H.,Hanifin, J. William Jr.,Relles, Howars M.
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p. 275 - 280
(2007/10/02)
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- Reactions of cyclopropylcarbinol in dilute hydrochloric acid
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The treatment of cyclopropylcarbinol (1-OH) with dilute HCl has been used as a method for the preparation of cyclobutanol (2-OH).While 2-OH is the major product in this reaction, a careful investigation showed the presence of a total of 13 products, namely the alcohols 1-OH, 2-OH, and allylcarbinol (3-OH), cyclopropylcarbinyl, cyclobutyl and allylcarbinyl chlorides (1-Cl, 2-Cl and 3-Cl, respectively), dicyclopropylcarbinyl, cyclobutyl cyclopropylcarbinyl, allycarbinyl cyclopropylcarbinyl, dicyclobutyl and allylcarbinyl cyclobutyl ethers (1-O-1, 2-O-1, 3-O-1, 2-O-2, and 3-O-2, respectively), as well as butyraldehyde and isobutyraldehyde.The alcohols, chlorides, and ethers likely arose from reactions of the bicyclobutonium ion with available nucleophiles in the reaction mixture.The minor amounts of the two aldehydes may be due to a ring opening isomerization of 2-methylcyclopropanol, the latter in turn resulted from a net 1,3-hydride shift in the cyclopropylcarbinyl cation, probably via an edge-protonated cyclopropane-type of species.Treatment of cyclopropylcarbinol (1-OH-α-14C) with dilute HCl gave samples of 1-OH-x-14C, 2-OH-x-14C, and 3-OH-x-14C the degradation of which showed that all three methylene groups in these alcohols have become equivalent, indicating a complete equilibration between isotope-position labeled bicyclobutonium ions.
- Lee, Choi Chuck,Cessna, Allan J.
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p. 1075 - 1079
(2007/10/02)
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