Intermolecular dehydrohalogenation

Potential Non-Cvcllc Precursors of Preceramic Polymers. Boranes such as bis(trimethylsilyl(aminotrimethylsilylaminochloroboranes can be viewed as monomers for preceramic polymer and, ultimately, boron nitride production. Intermolecular dehydrohalogenation of this borane would be thus expected to yield either the dimer or the polymeric system. 

From the results of the small scale thermal analysis experiments previously reported (23,25), it was concluded that the antimony volatilization and bromide release observed for ternary mixtures containing organobromine compounds, which did not undergo intermolecular dehydrohalogenation, could not be accounted for solely on the basis of HBr formation during degradation. 

Intermolecular dehydrohalogenation [1, 1203, before references]. A solution of cyclohexanecarbonyl chloride (Eastman) in benzene is stirred and swept with... 

Another group of reactions can be classified as intermolecular dehalogenations or dehydrohalogenations, based on Wurtz-, Fittig-, Ullmann-, Grignard-, or Friedel-Crafts reactions. Thus, polyphenylenes may be obtained by polycondensations of p-dichlorobenzene in the presence of Na/K alloy83-85. ... 

The intermolecular alkylation of metallo nitronates with various alkyl halides is limited. The addition of methyl iodide to the silver salt of an aryl nitro-methane provides the corresponding methyl nitronate in moderate yield (Eq. 2.13) (150), which has also been extended to the silver salt of trinitromethane (Scheme 2.16) (151-153). However, in the case of primary halides, both O- and C-alkylation are observed. For secondary and tertiary halides, only O-alkylation is observed, but in low yields. Unfortunately, under the reaction conditions, the starting alkyl halide can undergo dehydrohalogenation to provide the corresponding alkene, which then undergoes [3+2] cycloaddition with the alkyl nitronate. 

Ketene reactivity in intramolecular cycloadditions parallel those in intermolecular reactions in which chloro-, vinyl-, aryl- and alkoxyketenes are more reactive than the alkylketenes. In most instances the ketene is generated by amine dehydrohalogenation of an acid chloride. There are, however, a few examples of ketenes prepared along less conventional routes as by the examples for the formation of 11.150 12,151 and 13.151... 

Dealkylation of tertiary amines with dibenzoyl peroxide, 44, 74 Decarboxylation, intermolecular, of isocyanates to carbodiimides, 43,32 Decker synthesis of amines, 44, 7t, 75 Dehalogenation of l,l,2-trichloro-2,3,3-trifluorocydobutane, 42,45 Dehydration, of formamides with phosphorus oxychloride to isocy-anides, 41, 13, 101 of 4- 2-hydroxyethyl)piperidine to quinuclidine, 44, 90 Dehydrohalogenation of 2-chloroallyl-amines to propargylamines, 44,55 Delepine reaction, to prepare 2-bromo-allylamine, 43, 6 Deoxyanisoin, 40,16 Deoxybenzoin, 40, IT Deoxypiperoin, 40, IT Deaylamine, 41, 8T... 

The decomposition of cyclic sulfones and sulfoxides has attracted increasing attention recently in view of their relationship to cyclic fragmentation reactions and of the dramatic impact of the Woodward-Hoffman rules for intermolecular cycloaddition and electrocyclic ring opening reactions. The simplest cyclic sulfone known is 2,3-diphenyl thiirene-1,1-dioxide (A) which was isolated by Carpino and McAdams by the Ramberg-Backlund base catalyzed dehydrohalogenation of a, a -dibromodibenzylsulfone, viz. 

If the two halogens are on the same or adjacent carbons, two consecutive E2 dehydrohalogenations can result in the formation of a triple bond. The Williamson ether synthesis involves the reaction of an alkyl halide with an alkoxide ion. If the two functional groups of a bifunctional molecule can react with each other, both intermolecular and intramolecular reactions can occur. The reaction that is more likely to occur depends on the concentration of the bifunctional molecule and the size of the ring that will be formed in the intramolecular reaction. 

The aryl-aryl bond formation can be realized in the photochemical manner by irradiation of aryl iodides or bromides such as la which, by photo-dehydrohalogenation, give biaryls lla [90-92], Scheme 47. However, the photochemical synthesis of biaryls have also been performed as an intermolecular process [93]. The reactions are usually performed by irradiation of the given substrate in benzene or cyclohexane solution in the quartz-glass vessel, under the UV-light of... 

---