From Tetrachlorocyclopropene

Addition of dichlorocarbene to trichloroethylene gave pentachlorocyclopropane which was smoothly dehydrochlorinated by aqueous potassium hydroxide into tetrachlorocyclopropene 14 19). On heating at 150-180 °C, 14 provided an efficient source for tetrachlorovinylcarbene 15, which could be trapped intermolecularly by olefins to give the l-chloro-l-(trichlorovinyl)cyclopropanes 16, Eq. (7)20). 

Alternatively, 1,1,3,3- and 1,2,3,3-tetrachloropropene 21 and 22 or 1,1,2,3,3 penta-chloropropane 23 underwent dehydrochlorination with potassium t-butoxide to give, probably through 1,3,3-trichloropropyne 24, the dichlorovinylidenecarbene 25 which was trapped by olefins to lead to the dichloroethenylidenecyclopropanes 26. Then, the highly reactive allene 26 added electrophiles as well as nucleophiles such as methoxides to give, for instance, l-methoxy(2-chloroethynyl)cyclopropane 27, Eq. (9) 22). 

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To use the reaction leading to the triaminocyclopropenium ion from tetrachlorocyclopropene, which is considered to be the simplest way, seems inappropriate because the reaction of tetrachlorocyclopropene (4) with protic nucleophiles such as alcohol and water yields the ring-opened products ) as shown in Eqs. (1) and (2). 

By employing a l-aryl-2,3,3-trichlorocyclopropene (easily available from tetrachlorocyclopropene—see equation 26) an analogous sequence of reactions can be performed to give the corresponding aryl-substituted derivatives. In particular the aryldiaminocyclopropenium ions (81) have provided a wide range of derivatives in... 

Support for this mechanism stems from isolation of diazo compound 181b from the analogous reaction of diester 180b. By comparison adduct 182 (from tetrachlorocyclopropene and phenyl azide) is extremely labile and gives acrylamide 183 upon nitrogen loss and hydrolysis. ... 

Apeloig et al. have recently provided X-ray crystallographic evidence for the structure of the product exo-2a, from tetrachlorocyclopropene and 1-acetoxybuta-l,3-diene, and established that only the evo-product was obtained. The products from 1 b and Ic have the same stereochemistry, because they can be related chemically to exo-2a. The exo stereochemistry in these reactions is apparently caused by unfavorable interaction between the diene and the 3,3-dihalo groups of the cyclopropene in the endo transition state. ... 

Cyclopropenium salts could be prepared in situ from tetrachlorocyclopropene and aluminum chloride. Reaction with a 1,2-diol or 1,2-dithiol rather than a simple alcohol led to acetals or dithioacetals. 

Trichlorocyclopropenylium ion, prepared from tetrachlorocyclopropene and aluminum trichloride in situ, reacted with tri- and dichloroethene to give disubstituted cyclopropene derivatives, which were readily hydrolyzed to cyclopropenones, c.g. I, ... 

The trianilinocyclopropcnylium salt, prepared from tetrachlorocyclopropene and A-trimethyl-silylaniline, was dehydrochlorinated with sodium hexamethyldisilazanidc at — 78 C in tetrahydrofuran to yield 2,3-dianilino-A-phenylcyclopropenimine (3), a nitrogen analog of deltic acid, in 72% yield. 

Secondary aminoacetylenes, which readily tautomerize to ketenimines, have been isolated and characterized for the first time by pyrolysis of 4-methylene-isoxazol-5(4//)-ones and trapping the products at -196 °C e.g. Scheme 115). Bis-dialkylaminocyclopropenones, prepared from tetrachlorocyclopropene and dialkylamines, pyrolize smoothly at 525 °C to furnish bis-dialkylamino-... 

This synthetic appproach has been used in a few cases for the preparation of pyridazines from diazo compounds and cyclopropenes. In general, cycloadducts (176) are formed first and these rearrange in the presence of acid or alkali to pyridazines (Scheme 98) (69TL2659, 76H(5)40l). Tetrachlorocyclopropene reacts similarly and it was found that the stability of the bicyclic intermediates is mainly dependent on substitution (78JCR(S)40, 78JCR(M)0582>. 

An interesting intermediate 30 was proposed to result from the sequential addition of pyridine to tetrachlorocyclopropene (31). Compound 30 represents an alkyl nitrogen ylide with two 1-chloroalkyl pyridinium moieties in the same molecule. Pyridines with electron-withdrawing groups and heterocycles with an electron-deficient nitrogen, for example, pyridine-3-carbaldehyde or quinoline, react with 31 to yield the corresponding mono-substituted products 32a and 32b (83JOC2629) (Scheme 8). 

Methyl 2-chloro-2-cyclopropylideneacetate (4) was readily prepared in two steps from ethylene and tetrachlorocyclopropene [7], and reacted with 4-methylcyclohexa-l,3-dien-2-ol trimethylsilyl ether (62a) at 60 °C to give a complex mixture containing about equal amounts of both regioisomeric adducts 63a, 64a besides the tricyclic ketoester 65a after acidic workup (Schemes 12 and 13) [15]. Each regioisomer was a mixture of endo and exo-diastereomers. The trimethylcyclohexadiene 62b yielded, after 2 days at 100 °C and acidic work-up, the tricyclic ketoester 65b as the main product (Schemes 12 and 13) [15]. 

Application of the usual hydrolysis procedures to tetrachlorocyclopropene does not lead to the formation of dichloro cyclopropenone (26). This unstable compound is obtained, however, by a special procedure from trichloro cyclopropenium tetra-chloroaluminate (24) via the AlCl3-adduct 2532. ... 

The outstanding chemical properties of bicyclopropylidene (1) were once again exemplified by its unprecedented addition to tetrachlorocyclopropene (TCCP). Reaction between 1 and TCCP occurred at 80 °C and led to 223 which was readily hydrolyzed to give 224. Adduct 223 apparently arises from a nucleophilic attack of 1, most probably in a 8 2 fashion, on TCCP which corresponds to a chloroene reaction (Scheme 50) [142]. 

The discovery of an easy route to a series of l-chloro-l-(trichlorovinyl)cyclopropanes from the thermal reaction of tetrachlorocyclopropene and olefins greatly promoted the availability and synthetic utility of alkynylcyclopropanes. Upon reductive elimination with two equivalents of n-BuLi in ether-hexane at -78 °C, a series of ring substituted... 

In cases such as the one shown in equation (69), what appears to be displacement is more likely a multistep elimination-addition process.37 Carbonyl or sulfonyl groups in the 2-position greatly facilitate each of these two steps. Thus (32) on treatment with alkoxide or thiolate gave the cyclopropane acetal or thioacetal, respectively (equation 70).199 In related work, tetrachlorocyclopropene, which has interesting synthetic potential, is formed from pentachlorocyclopropane by treatment with potassium hydroxide (equation 71).200 Certain 1,1,2-trihalocyclopropanes on reaction with methyllithium in ether at low temperature afford the corresponding halocyclopropenes by 1,2-dehalogenation (equation 72).201 Similarly,... 

Tetrachlorocyclopropene was prepared from sodium trichloroacetate and trichloroethylene.2 3 It is also available from the Aldrich Chemical Company, Inc., Eastman Organic Chemicals, and the Merck-Schuchardt Company (in Europe). 

Cycloaddition reactions of phenyl and tosyl azides to the strained double bond in cyclopropenes have been investigated.170il The reaction products from 3,3-dimethylcyclopropene indicate that the initially formed intermediate is a normal 1,3-dipolar adduct. Tetrachlorocyclopropene yields the primary adducts with several aryl azides. 70b However, cyclopropenedicarboxyl ester gives only unstable triazolines with phenyl and methyl azides.170 ... 

The primary adducts from the reaction of tetrachlorocyclopropene and azides yield chlorinated azabutadienes.170b The triazoline derived from Dewar benzene and phenyl azide, when heated in the presence of aluminum chloride, yields unique ring-enlarged heterocycles (Scheme 168).484... 

The kinetic data of the reaction have not been obtained yet because the process is so rapid. However, from the above results and discussions it might be deduced that the reaction of tetrachlorocyclopropene with a secondary amine leading to triamino- and diaminochlorocyclo-propenium ions might proceed as shown in Scheme 2. 

The de Meijere group has demonstrated that tetrachlorocyclopropene is a very convenient source for tetrachlorovinylcarbene, which could be trapped by a variety of olefins and provides an array of interesting chlorinated vinylcyclopropanes (equation 186) . Preparations starting from other precursors have also been reported . ... 

Cyclopropene and its deuterium-labelled derivatives can be obtained by the photo-decarbonylation of the corresponding furan at 254 nm but the method is of strictly limited value because of the photolability of many cyclopropenes (Section IV.B.2). West and his coworkers have shown that aryltrihalo- and diaryldihalocyclopropenes are available from classical Friedel-Crafts aromatic substitution reactions employing the cyclopropenyl cation as electrophile. Thus tetrachlorocyclopropene is converted to its derived cation which is then allowed to react with an aromatic compound. The exothermic reaction provides monoarylcyclopropene at low ( 0°C) temperature and the diaryl derivative at higher ( > 50° C) temperature (equation 26). In this way 2-phenyl-1,3,3-trichlorocyclopropene can be obtained in 58 % yield and the p-fluorophenyl analogue in... 

Rearrangement and elimination products of transient l,2,3-triazabicyclo[3.1.0]hex-2-enes are isolated from the reactions of cyclopropenes with azides. For example tetrachlorocyclopropene and trimethylsilyl azide afford triazine 177 from addition and subsequent loss of trimethylsilyl chloride (equation 62). Intramolecular rearrangement of... 

Tetrachlorocyclopropene (16), which is readily available from dehydrochlorination of 17 (equation 9) can be treated with strong Lewis acids to yield stable salts of the... 

Unsubstituted cyclopropenone was prepared by hydrolysis of the di- and trichloro-cyclopropenes obtained from the reduction of tetrachlorocyclopropene " . Treatment of the trichlorides 37 and 38 with SbCls affords the hexachloroantimonate salt of... 

The first example of a stable and isolable salt of a tetracation, composed of four directly bonded cyclopropenylium rings, was synthesized by the direct reaction of l,2-bis(diisopropyl-amino)-3-lithiocyclopropenylium perchlorate (10) with tetrachlorocyclopropene. Apparently this tetracation is stabilized by the resonance contribution from the structures containing both the triafulvene- and radialene-type -conjugated systems. ... 

A suspension of 1,2,3-trichlorocyclopropenylium tetrachloroaluminate in CH2CI2 (20 mL) was prepared from AICI3 (1.33 g, 10 mmol) and tetrachlorocyclopropene (1.96 g, 11 mmol). After 15 min, CH2CI2 (80 mL) was added, and the suspension was cooled to — 42 "C. To the strirred suspension was added dropwise over 30 min l-(trimethylsilyl)propyne (2.27 g, 20 mmol). The solution was stirred for 1 h at — 42°C and allowed to reach 20 C over 1 h. It was then poured into ice-water, and the organic layer was further washed with H2O and dried. After evaporation of the solvent, the remaining brown oil was purified by flash chromatography (hexane/EtOAc 95 5 to 8 2). Recrystallization (EtjO) gave moisture-sensitive, colorless crystals yield 0.647 g (50%) mp 109 110 C. 

A mixture of freshly distilled 3-chloro-l-propene (allyl chloride) (20.4 g, 0.267 mol) and tetrachlorocyclopropene (19.0 g, 0.107 mol) was heated in a sealed thick-walled glass ampoule at 170CC for 18 h. After carefully opening the ampoule, low-boiling components were trap-to-trap distilled at rt under reduced pressure (0.05 Torr), and the product distilled from the residue over a 35-cm Vigreux column yield 16.39 g (66%) bp 52°C/0.05 Torr ratio (cisjtrans) 2.1 1. 

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