Electrophilic addition of chloroform

Figure 12. Electrophilic addition of chloroform to C70and the subsequent hydrolysis. 

An electrophilic addition of chloroform to SWNTs was followed by hydrolysis and it resulted in the addition of hydroxyl groups to the surface of the nanotubes. Its esterification with propionyl chloride led to the corresponding ester derivatives (Tagmatarchis et al., 2002). 

The electrophilic addition of hydrogen sulfide and 1-butanethiol to 1,3-conjugated dienes49 in chloroform at —10 °C has been reported in a quite old paper of a Russian team. The yields were generally low, in the range of 20%, even when the reaction was catalyzed by a mixture of two Lewis acids, EtAlB /EtAlC however, polymerization of the diene was not significant. 

Typical chlorinations of alkanes or alkenes with (dichloroiodo)benzene proceed via a radical mechanism and generally require photochemical conditions or the presence of radical initiators in solvents of low polarity, such as chloroform or carbon tetrachloride. However, the alternative ionic pathways are also possible due to the electrophilic properties of the iodine atom in PhICH or electrophilic addition of CI2 generated by the dissociation of the reagent. An alternative synchronous molecular addition mechanism in the reactions of PhICl2 with alkenes has also been discussed and was found to be theoretically feasible [44]. The general reactivity patterns of ArICh were discussed in detail in several earlier reviews [8, 45, 46]. 

Chlorination and chloramination of a widely used antibacterial additive, triclo-san, which is used in many household personal care products, results in the formation of chloroform, 5,6-dichloro-2-(2,4-dichlorophenoxy)phenol, 4,5-dichloro-2-(2,4-dichlorophenoxy)phenol, 4,5,6-trichloro-2-(2,4-dichlorophenoxy)phenol, 2, 4-dichlorophenol, and 2,4,6-trichlorophenol [119]. The reaction of triclosan with monochloramine is slow, however, compared to chlorine [120]. The chlorophenox-yphenols are formed via bimolecular electrophilic substitution of triclosan. 

Although the chemistry of pentatetraenylidene complexes [M]=C(=C)3=CR R has not received as much attention as that of aUenylidenes, there is ample experimental evidence to confirm the electrophilic character of the C, Cy and carbons of the cumulenic chain [26-29, 31]. Thus, treatment of tra s-[RuCl(=C=C=C=C=CPh2) (dppe)2][PFg] (132) with alcohols or secondary amines resulted in addition of the nucleophilic solvent across the Cy=Cs double bond to give alkenyl-allenylidenes 138 (Scheme 48) [358]. In chloroform, electrophilic cyclization with one of the Ph groups occurred to give 139. This transformation is actually the parent of the later observed allenylidene to indenylidene intramolecular rearrangement (Scheme 15). 

The stoichiometric equivalents of halogen fluorides, i.e. chlorine monofluoride, bromine monofluoride and iodine monofluoride, have found a wide application in addition reactions to double bonds. The equivalents are obtained by reacting A -haloamides or free halogens in combination with hydrogen fluoride or its salts as the source of fluoride ions. The reactions proceed under mild conditions at — 80 to 20 "C in anhydrous hydrofluoric acid or diethyl ether, tetrahydro-furan, dichloromethane or chloroform mainly by electrophilic addition with Markovnikov-type regioselectivity (anti addition).26-28... 

Cabaleiro and Johnson (1967) report that the addition of chlorine to -methyl cinnamate in chloroform or acetic acid is syn-selective, SS 0-75, in chloroform and acetic acid acetoxychloro derivatives are produced as well. Again, Dewar and Fahey (1964) argue that the normal course of addition of hydrogen halides onto olefins is a polar electrophilic process involving classical carbonium ions as intermediates and leading mostly but not exclusively to cis-adducts. A syn-preference was found in the additions of deuterium bromide to acenaphthylene, indene, and cis- and fraws-phenylpropene. In the case of indene, phenylpropene and methyl cinnamate, which are styrene analogs, concerted syn addition is symmetry-allowed (see bottom of p. 273). 

Treatment of 4-ethoxy-6-methylpyrimidine-l-oxide (602) with acetic anhydride at 25-35 °C in chloroform followed by the addition of diketene at <20°C caused an exothermic reaction from which was isolated 7-acetyl-4-ethoxy-2-methyloxazolo[4,5-c]pyridine (603) (22%) and 7-acetyl-4-ethoxy-3-methylisoxazolo[4,5-c]pyridine (604) (8%) (88CPB168). A plausible mechanism for the formation of the isomers (603) and (604) is shown in Scheme 77. Acetylation with acetic anhydride furnishes an initial intermediate, l,2-diacetoxy-l,2-dihydropyrimidine (605). Electrophilic attack by diketene at C-5 then yields an acetoacetyl intermediate (606). Ring-opening and recyclization of (606) then gives via intermediates (607) and (608) the pyridine (609). Compound (609), which is not... 

Deprotonation of other bicyclic ketones in the presence of LiCl has shown similar results (Scheme 23). Interestingly, deprotonation of tropinone (32) by 27 and using benzyl chloroformate as the electrophile resulted in ring opening to yield the enone 34 (Scheme 23a)55,56. The ee increased from 45% up to 62% upon addition of LiCl. The effect of LiCl on the enantioselectivity is also displayed in the reactions of 35 and 37 to give 36 and 38, respectively, in Schemes 23b and 23c53,54,57. 

It is often difficult to make a comparison between the various results obtained for the same polyenes as different reaction conditions (ratio of reactants, temperature, time) were used in each case. The addition of dichlorocarbene (chloroform/base/phase-transfer catalysis) to straight chain and cyclic unconjugated di- and trienes, carried out under identical conditions but varying the catalysts, showed the peculiar properties of tetramethylammonium chloride. Under precisely tailored conditions, either highly selective mono- or polyaddition of dichlorocarbene to the polyenes is possible tetramethylammonium chloride was the most efficient catalyst for monocyclopropanation. (For the unusual properties of tetramethylammonium salts on the phase-transfer catalyzed reaction of chloroform with electrophilic alkenes see Section 1.2.1.4.2.1.8.2. and likewise for the reaction of bromoform with allylic halides, see Section 1.2.1.4.3.1.5.1.). For example, cyclopropanation of 2 with various phase-transfer catalysts to give mixtures of 3, 4, and 5, ° of 6 to give 7 and 8, ° and of 9 to give 10 and 11. °... 

The a proton of a substituted cyclopropane is also rendered acidic if the substituent is attached to the ring by C-P bonds. A few reports have appeared on a-substitution in such compounds.(Cyclopropyl)triphenylphosphonium bromide was converted to a (1-ethoxy-carbonylcyclopropyl)triphenylphosphonium salt 18 in 80% yield by sequential treatment with lithium diisopropylamide and ethyl chloroformate. Furthermore, some diethyl cyclopropyl-phosphonates were converted, in some cases in excellent yield, to diethyl (1-hydroxymethyl-cyclopropyl)phosphonates by treatment with lithium diisopropylamide followed by addition of an aldehyde." Thus, typically, diethyl 2-hexylcyclopropylphosphonate gave diethyl 2-hexyl-l-[hydroxy(phenyl)methyl] cyclopropylphosphonate (19b) in 90% yield on reaction with benzaldehyde. ° Other electrophiles such as acetone, acetyl chloride, acetic anhydride, and ethyl acetate, were not sufficiently reactive to undergo addition to the anion. 

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