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The mechanism for the unusual AlCl3-catalyzed rearrangement of 2,2-dichloronorbornane to 1-chloronorbornane in pentane has been elucidated; the reaction, which also yields four isomeric dichloronorbornanes, occurs in three steps: (1) ionization

1-Norbornyloxychlorocarbene (1-NorOCCl), 1-bicyclo[2.2.2]octyloxychlorocarbene (1-BcoOCCl), and 1-adamantyloxychlorocarbene (1-AdOCCl) were generated in dichloroethane (DCE) by photolysis of the appropriate diazirines. The exclusive product in each case was the bridgehead alkyl chloride formed by fragmentation of the carbene to [R+ OC Cl-] ion pairs, loss of CO, and cation-anion collapse. In mixtures of methanol and DCE, each carbene gave three products: RCl, ROH, and ROMe. RCl and ROMe resulted from competition between ion pair collapse and methanol capture of the cation. ROH resulted from methanol capture of the carbene (before fragmentation), followed by eventual methanolysis and hydrolysis of ROCH(Cl)OMe. The ratios of carbene capture to carbene fragmentation fell in the order 1-NorOCCl > BcoOCCl > 1-AdOCCl; 1-Nor+ was the least stable cation and the slowest to form by fragmentation, so that this carbene was the most readily captured. This trend was accentuated in methanol-pentane mixtures, where ionic fragmentation was further slowed in the less polar solvent. Laser flash photolysis with either UV or time-resolved infrared (TRIR) monitoring permitted the determination of the absolute rate constants for fragmentations of the carbenes in DCE at 25 °C. The rate constants (s-1) were: 1-NorOCCl (3.3 × 104), 1-BcoOCCl (1.5 × 105), and 1-AdOCCl (5.9 × 105). The rate constants decreased in the order of increasing strain in the resulting bridgehead carbocation, but the range of rate constants was compressed to a factor of only ～18. This constrasts with the factor of 1010 by which the acetolysis of 1-AdOTs at 70 °C exceeded that of 1-NorOTs. The fragmentation of 1-NorOCCl to the ion pair was 3 × 1015 times faster than the acetolysis of 1-NorOTs. The activation energies were measured as 9.0 kcal/mol (log A = 11.2 s-1) for the fragmentation of 1-NorOCCl and 4.4 kcal/mol (log A = 8.44 s-1) for that of 1-BcoOCCl both in DCE. B3LYP/6-31G* computed activation energies in simulated DCE were 14.6 and 2.7 kcal/mol, respectively. Copyright

A series of 1-halonorbornanes was used as a model system in reactions with several nucleophiles in order to determine the involvement of single electron transfer (SET) in nucleophilic aliphatic substitution in the absence of light.The 1-halonorbornanes were allowed to react with Me3Sn(1-), Ph2P(1-), AlH4(1-), N(iPr)2(1-), SPh(1-), and the 2-nitropropyl anion in the ether solvents at room temperature to 0 deg C.The results of product analyses, the use of radical and radical anion trapping reagents, the results of deuterium labeling studies, and the nucleofugality effect support a SET mechanism for the reactions involving 1-iodonorbornane.Convincing evidence that reduction of hindered alkyl iodides with LiAlH4 takes place by a SET pathway rather than by an impurity-initiated halogen atom radical chain process followed by an SN2 pathway, is presented.

Fluorodeiodination is found to be an attractive procedure for the synthesis of bridgehead fluorides.Thus, treatment of the corresponding iodide with xenon difluoride in dichloromethane at ambient temperature generally leads to high yields of the fluoride.Evidence suggests the intermediacy of the bridgehead cation in this reaction, and accordingly the substrates which are unfavorable disposed to fluorodeiodination are the bicycloalkyl iodides.In this context the isolation of a small quantity of methyl 4-fluorobicyclohexane-1-carboxylate (46, R= COOMe) is significant because it represents the first occasion on which the elusive 1-bicyclohexyl cation has been trapped.We have also demonstrated that synthesis of the iodides themselves can be accomplished efficiently both by Barton halodecarboxylation and by treatment of the carboxylic acid with lead tetraacetate and iodine.

Bridgehead carboxylic acids can be converted into their corresponding chlorides very efficiently under Barton halodecarboxylation conditions.Addition of the acid chloride to a suspension of the sodium salt of 1-hydroxypyridine-2(1H)-thione in boiling carbon tetrachloride under irradiation leads to excellent yields of the bridgehead chloride via the derived thiohydroxamic ester.In a useful modification for the synthesis of volatile halides, either 1,1,1-trichloro-2,2,2-trifluoroethane or trichlorofluoromethane can be employed as substitute solvents.It is found that the Barton procedure is applicable to the synthesis of labile bromides such as 1-bromobicycloheptane for which the usual Hunsdiecker reaction fails.For these, and other brominations, 2-bromo-2-chloro-1,1,1-trifluoroethane ('Halothane') is shown to function as an efficient solvent/bromine atom donor.

The synthesis and decomposition of N-(n-butyl)-N',N'-dimethyl-N-nitrosourea (2a), N-(n-butyl)-N',N'-dimethyl-N-nitrourea (3a), N',N'-dimethyl N-(1-norbornyl)-N-nitrosourea (2b), N',N'-dimethyl-N-(1-norbornyl)-N-nitrourea (3b) are described.Several of the compounds show complex NMR spectra ascribable to rotational isomerism.Decomposition of 2a and 3a gave n-butyl N,N-dimethylcarbamate and tetramethylurea, while decompostion of 2b and 3b in methylene chloride gave 1-norbornyl N,N-dimethylcarbamate and 1-norbornyl chloride.These products are formed via diazotic acid derivatives and carbonium ion pairs; the reaction mechanism is essentially the same as that established for the closely related N-nitrosoamides.In concentrated solutions, nitrosourea 2a yielded a new product, amino acid 20.

The nitrosation of N-alkyl-O-acylhydroxylamines leads to immediate decomposition at dry ice temperatures; the corresponding ester and nitrous oxide are formed.An 18O study has shown that the nitroso-O-acylhydroxylamines fragment directly rather than undergo a rearrangement reaction (as observed with the nitrosoamides).The product yields are respectable, especially at low tempreatures, and the method has promise for the generation of high energy carbonium ions.

The thermal decomposition of several N-alkyl-N-nitroso-4-toluenesulfonamides, N-alkyl-N-nitro-4-toluenesulfonamides, and N-alkyl-N'-(4-toluenesulfonyloxy)diimide N-oxides was undertaken to determine whether the basicity of the negatively charged counterion in deamination reactions was a reaction variable.The nitrososulfonamides decompose following first-order kinetics to give the corresponding esters with retention of configuration.The reaction characteristics are very similar to those of the N-nitrosocarboxamides, and the reaction mechanisms are presumably very similar also.The N-nitrosulfonamides required high temperatures for decomposition, and they gave an anomalous set of products: amide (by denitration) and olefins, but no nitrous oxide or toluenesulfonate esters.The N'-toluenesulfonoxydiimide N-oxides, isomeric to the nitrosulfonamides, proved to be surprisingly stable compounds; they decompose by first-order kinetics to yield the corresponding esters and nitrous oxide.

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.

Bent ?-radicals 3a-i, generated from alkylmercuric salts 1 and/or peresters 2, were treated with a BrCCl3/CCl4 competition system at different temperatures.Exner-analysis of these selectivity data (table 1) shows, that radicals of sp2 type 3a-d and bridgehead radicals 3e-i follow different isoselective relationships (figure 1, 2).Reversal of the selectivity row occurs at 310 and 210 K, respectively.Above of these isoselective temperatures less shielded radicals are more selective than more shielded radicals because entropy effects overcompensate enthalpy effects (table 2).Comparison with ?-radicals 6 shows, that each type of carbon radicals follows an isoselective relationship by its own.

Single-crystal epr of (nor)4Cr showed the molecule to have an isotropic g factor for the Δm = 1 transition. There were no Δm = 2 and double-quantum transitions; therefore D ≈ E ≈ O. In most organic glass these transitions become allowed. (nor)4Cr apparently assumes several conformations in isooctane and cyclohexane glasses which are distinguishable by their zero-field splitting parameters. Among all the solvents examined benzene perturbs the ligand field symmetry the least. Only a weak Δm = 2 signal was occasionally detected; there was no double-quantum transition even at highest available microwave power.