Elimination of chloroform

The introduction of sulfur between two ortho amino groups is the oldest and still the most commonly used route to benzo- and heteroarene-fused 1,2,5-thiadiazoles. The reaction has been extensively reviewed in both CHECK 1984) and CHEG-II(1996). The in situ preparation of Ar-sulfinylanilinc via /3-elimination of chloroform from trichlorometh-anesulfinamides 200 was recently supported by trapping with 1,2-benzenediamine to give the benzothiadiazole 2 in 85% yield (Equation 43) <1997TL487>. 

In humans. Fry et al. (1972) administered 500 mg of chloroform orally in olive oil in capsular form and found that 17-67% of the total dose of chloroform was exhaled as imchanged parent compound, and that the extent of pulmonary elimination of chloroform was governed inversely by the amount of adipose tissue on the individual ingesting the chloroform. The study also found that most of the chloroform tended to be exhaled between 40 minutes and 2 hours after dosing, which coincided with peak blood levels of chloroform produced at approximately 1 hour after dosing. 

The base-promoted a eliminations of chloroform or bromoform provide a simple method for the production of dihalocarbenes. These add readily to olefinic double bonds to give 1,1-dihalocyclopropanes. The halogens can be removed (one or both) by reduction the most common method is to use tri-n-butyltin hydride. 

Readily available allylic and benzylic hichloromethyl sulfoxides undergo an unusual base-induced /(-elimination of chloroform, with formation of the corresponding a,/ -unsaturated sulfine, under mild conditions at room temperature die procedure has been applied to form vinylthioaldehyde 5-oxides and vinylthioketone 5-oxides. 89 N-Sulfinylamines (115) have likewise been prepared by /(-elimination of chloroform from trich Ioromcthanesulfinamidcs (114).90 The reaction is promoted rapidly at room temperature by pyrrolidine and Ht N and the sulfinylamines (115) can be trapped by o-phenylenediamme (116), to give benzothiadiazole, before desulfonative hydrolysis occurs. 

This amino olefin was first prepared by thermal elimination of chloroform from 1,3-diphenyl-2-trichIormethy]imidazolidine,2and later by the procedure described here.3, 1 It can also be made by treatment of 1,3-diphenylimidazolinium salts with strong bases.5, 6... 

A novel synthesis of a-unsaturated sulfines has been introduced by Bra-verman et al. [99]. Et3N or DABCO treatment of allylic and benzylic tri-chloromethyl sulfoxides triggered the elimination of chloroform and formation of the sulfines. It must be stressed that these sulfines are thermally relatively stable, and this stands in high contrast to the corresponding thio-carbonyl compounds unsaturated thioaldehydes cannot be monitored under the same experimental conditions and have to be used at very low temperature or trapped in situ. The first synthesis of thioacrolein S-oxide was achieved by flash vacuum thermolysis of an anthracene allyl sulfoxide [100], and both isomers in a (Z E) ratio of 78 22 were characterised by NMR spectroscopy at -60 °C. 

During the early attempts to synthesize free NHC, Wanzlick and colleagues tried to prepare l,3-diphenylimidazolidin-2-ylidene (2) by thermal elimination of chloroform from 1, but they rather obtained the dimeric electron-rich olefin 3 (Scheme 1) [15-17]. Wanzlick postulated that the carbene 2 could be formed as an intermediate during the formation of 3, and proposed the existence of an equilibrium between 2 and 3. Evidence supporting this equilibrium came later with the works performed by the research groups of Denk, Hahn, Lemal, and Cavell [18-21]. 

The use of selectivity data as a means of identifying intermediates has been employed effectively. For example, in the dichlorocyclo-propanation of olefins, the selectivity of attack using CC12 generated by different methods (the pyrolysis and a elimination of chloroform) was found to be almost identical (Skell and Cholod, 1969a). This was... 

The mass spectrum of dicofol (a diphenylmethanol derivative) depends on the type of inlet system used on the mass spectrometer. The spectrum obtained by GC-MS (Fig. 3A) is identical with that of pp -dichlorobenzophenone, presumably formed by elimination of chloroform from the parent compound in the heated injection port. On the other hand, the direct insertion probe spectrum (Fig. 3B)... 

The formylation, i.e., formal carbon monoxide (CO) insertion, of phenols using chloroform and aqueous base is known as the Reimer-Tiemann reaction (Scheme l).73 It is generally accepted that base-induced a-elimination of chloroform (CHC13) yields the rate-determining, electrophilic dichlorocarbene (CC12) intermediate, which... 

Use in synthesis. Wadsworth and Emmons condensed diethyl phosphonate with carbon tetrachloride and cyclohexylamine according to A. R. Todd (1945) to produce diethyl cyclohexylaminephosphoramidate (3). The initially formed trichloro-methylphosphonate (2) reacts with a second mole of amine with elimination of chloroform to give (3). Treatment of this phosphoramidate with sodium hydride in... 

Moderate yields (30-48%) are claimed for the disubstituted 1,3,5-triazine formed on elimination of chloroform from dihydrotriazine (146), on treatment with sodium hydroxide (see Section... 

Certain allylic and benzylic trichloromethyl sulfoxides suffer elimination of chloroform on exposure to tertiary amine bases. ... 

Parallel to these efforts, Wanzlick tried to prepare a stable N-heterocyclic carbene by a-elimination of chloroform from 5. The free carbene, however, could not be isolated and instead its dimer, the entetraamine 6=6, was always obtained (Scheme 1.2). Wanzlick s initially postulated cleavage of the entetraamine according to 6=62x6 could not be demonstrated conclusively. Cross-metathesis experiments with differently -substituted entetraamines failed, excluding an equilibrium between the monomer 6 and the dimer 6=6 (Scheme 1.2). " ... 

Wanzlick and Schikora were the first to attempt the preparation of saturated imidazolin-2-ylidenes by an a-elimination of chloroform from imidazoline derivatives but could only obtain the electron-rich entetraamines (see Scheme 1.2). It was Arduengo et al. who presented the first stable crystalline imidazolin-2-ylidene 86 (Figure 1.8) obtained by deprotonation of the corresponding imidazolinium salt. " Shortly thereafter, Denk et al. used the reductive desulfurization of imidazolin-2-thiones to obtain the N,N -A tert-butyl) substituted stable carbene of type 86 and the entetraamine 86=86 with the sterically less demanding A,A -dimethyl substituents (Figure 1.8). Additional imidazolin-2-ylidenes with varying A,A -substituents were obtained by... 

In the following example reaction of this sort [10], the prior equilibrium became apparent in the curvature of a plot as will be seen below. Treatment of 1,1-diphenyltrichloroethanol with sodium hydroxide caused elimination of chloroform. The proposed mechanism is shown in Equation 4.25. In this reaction, the anionic intermediates were present in low concentrations and not detected directly. A unique feature here is that the concentration of OH" does not change because it is regenerated in the third step. Therefore, pseudo-first-order conditions exist at any concentration of OH". Measurements showed that the reaction is pseudo-first-order in the chloroalcohol and also first order in OH"... 

Wanzlick et al. were the first to attempt the preparation of saturated imid-azolin-2-ylidenes by a-elimination of chloroform from imidazoline derivatives. They could, however, only isolate the electron-rich entetraamines (see Scheme 1.2). It was Arduengo et al who presented the first stable crystalline... 

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