2.2- dichloro-1 -methylcyclopropane

In strong base, propene reacts with chloroform to yield 2,2-dichloro-1 -methylcyclopropane. 

Phase transfer-catalyzed reactions have recently been employed to dehydro-halogenate gem-dihalocyclopropanes [156, 157]. Thus, 1-methylene-2-vinylcyclo-propane has been prepared from l,l-dichloro-2-ethyl-3-methylcyclopropane in 60 % yield. Under the reactipn conditions (solid KOH, DMSO in the presence of dibenzo-18-crown-6, 100-130 °C) further transformations may take place, however. For example, monoalkylated cyclopropanes have been converted to mixtures of acyclic enynes and conjugated trienes. And 7,7-dichloronorcarane is converted to toluene under these conditions. 

Finally, the formation of chlorocyclobutenes 25 and 27 by treatment of trimethylcyclopropene 24 with dichlorocarbene,2n and by reaction of l,l-dibromo-2,2-dichloro-3-chloromethyl-3-methylcyclopropane (26) with methyllithium 212 can be explained by disrotatory outward ring opening of an intermediate dichlorobicyclobutane with concomitant migration of an endo-ch a-rine and methylation, respectively. 

Method A CHClj, base, PTC Method B PhHgCBrClj, A. Additionally l,l-dichloro-2-(dich-loromethoxymethyl)-2-methylcyclopropane was formed (20%), the mixture was separated by GC. The mixture was separated by GC, the isomer with shorter retention time mp 39 -40 C. Isomer ratio 48 52. Isomer ratio 1 1. Additionally l,l-dichloro-2-(2-dichloromethoxyethyl)-2-methylcydo-... 

Reductive alkylation is one of several reactions that occurs when l,l-dichloro-2,2,3,3-tetra-methylcyclopropane and 7,7-dichlorobicyclo[4.1.0]heptane are exposed to magnesium-anthracene in tetrahydrofuran. The best results were obtained with 7,7-dichloro-bicyclo[4.1.0]heptane, which gave 9-(bicyclo[4.1.0]hept-7-yl)-9,10-dihydroanthracene and 9,10-bis(bicycIo[4.1.0]hept-7-yl)-9,10-dihydroanthracene in 44 and 34% yield, respectively. 

Reactions of this type result in formation of 1,1-dihalocyclopropanes. Such compounds are available by a large number of alternative routes, and this may explain why only a couple of such syntheses have been reported. The most efficient process converts 2-aryl-1,1-dichloro-2-methylcyclopropanes into the corresponding 3-aryl-l, 1,2,2-tetrachloro-3-trichloromethylcyclo-propanes, which is achieved by chlorine treatment. " When the reaction was carried out with l,l-dichloro-2-methyl-2-phenylcyclopropane, l,l,2,2-tetrachloro-3-phenyl-3-trichloromethyl-cyclopropane (1) was obtained in essentially quantitative yield. ... 

It is also possible to obtain methylenecydopropanes by monodehydrochlorination of compounds other than 1-chloro-l-methylcyclopropanes. For example, inverse addition of potassium terf-butoxide in dimethyl sulfoxide at 25°C to l,l-dichloro-2,2,3-trimethylcyclopropane (20) gave a 33% yield of 2-chloro-l,l-dimethyl-3-methylenecyclopropane (21) along with a 30% yield of ring-opened product 22. This is one case in which the usual double dehydrochlorination of 1,1-dichlorocyclopropanes (see Section 5.2.2.1.2.3.) is blocked and a single elimination occurs instead. Another example is the reaction of l-chloro-2,3-dimethylcyclopropane (23) with potassium tcr/-butoxide in dimethyl sulfoxide at 80-90 to give l-methyl-2-methyl-enecyclopropane (24) in 84% yield (see also below and Sections 5.2.2.1.1.1.2. and 5.2.2.1.1.2.). 

BuOK (84 g, 0.75 mol) was added to DMSO (400 mL) in a creased flask fitted with stirrer and condenser. l,l-Dichloro-2-ethyl-3-methylcyclopropane(2, 38 g, 0.25 mol) was added dropwise at 25"C under N2 (external cooling). After 2 h, the product was isolated by addition to ice-water, pentane extraction, drying (Na2S04) and removal of pentane at 25"C yield 62% (determined by GC). 

When a side chain larger than methyl is not present, diene products are not formed. Thus, for example, 1,1 -dichloro-2,3-dimethylcyclopropane does not give bis(methylene)cyclopropane but rather products derived from double dehydrochlorination followed by addition of base (see Section 5.2.2.1.3.). l,l-Dichloro-2-methylcyclopropane gives only polymeric material, presumably due to the fact that the cyclopropene intermediate has no avenue of escape for the double bond from the three-membered ring. ... 

When no other nucleophile is added, only one mol of tert-butoxide adds to the substrate. Thus, reaction of 2-(bromomethyl)-l, 1 -dichlorocyclopropane (27) with potassium tert-butoxide in tcr/-butyl alcohol gives a 49yo yield of /ra 5-l-tert-butoxy-2-chloro-3-methylenecyclo-propane (28), along with 9% of ring-opened product 29. The same methylenecyclopropyl ether 28 was obtained from the reaction of 2-bromo-l,l-dichloro-3-methylcyclopropane (30) with potassium tert-butoxide. 

Photochlorination of cyclopropane gave chlorocyclopropane (la) and 1,3-dichloro-propane. The latter was the major product at low temperature. Photochlorination with tert-h Ay hypochlorite gave mostly chlorocyclopropane (la). Methylcyclopropane reacted with chlorine to give predominantly l-chloro-2-methylcyclopropane (lb), but small amounts of acyclic products such as 2-chlorobutane, 1,3-dichlorobutane, and 1,3-dichloro-2-methyl-propane were also obtained. With ferr-butyl hypochlorite 4-chlorobut-l-ene was isolated as the only acyclic product. Photochlorination of 1,1-dimethylcyclopropane in trichloro-fluoromethane atO°C gave the chloromethylcyclopropane derivative 2 in 67% yield after immediate workup. 

The increased strain in methylenecyclopropane, which is relieved on ring opening, makes the cyclic bonds more liable to cleavage than methylcyclopropane. Photochlorination of methylenecyclopropane (3) in the liquid phase produced a mixture of several addition products including 3-chloro-2-chloromethylprop-2-ene (42%), 2,4-dichlorobut-l-ene (27%), 1-chloro-l-chloromethylcyclopropane (18 /o), 1,2,3,4-tetrachlorobutane (11 %), and 1,3-dichloro-2-chloro-methylprop-l-ene (2%). ... 

Methylcyclopropane shows strikingly different reactivity toward chlorine and bromine under radical chain conditions in CHjClj solution. The main product with chlorine is chloromethylcyclopropane (56%), along with smaller amounts of 1,3-dichlorobutane and l,3-dichloro-2-methylpropane. Bromine gives only... 

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