Chlorination of cyclopropanes

Cyclopropyl chlonde has been prepared by the free radical chlorination of cyclopropane Wnte a stepwise mechanism for this reaction... 

Chlorination of cyclopropane in the dark in a sealed tube at 35 °C in the presence of a catalytic amount of iron gave 1,3-dichloropropane (5) and 1,2-dichloropropane (6) as the major products. Diethylaminosulfonyl hypochlorite underwent addition across one of the most strained C — C bonds of quadricyclane to give a mixture of two stereoisomeric nortricyclane derivatives 7 and 8 and one rearrangement product 9. ... 

The notation for junctive processes is applicable to mechanisms of organic reactions as well. In the two alternative mechanisms for the free-radical chlorination of cyclopropane, the reaction pathway proceeds towards the transition state through either (201+202- [203] ) or (l,2)j - (201+202- [206] ), whereas the transition state transforms into products through either (l,l)d- ([203] -204+205) or (l,2)d- ([206] -204+205). 

Cyclopropane-fused chlorins are formed in good yields from copper porphyrins with ethyl diazoacetatc in benzene in the presence of copper(I) iodide.200,21 In the case of copper oc-taethylporphyrin 10, which gives a diastereomeric mixture of cyclopropane adducts 11, ethyl me o-porphyrincarboxylate 12 and a geminally dialkylated chlorin 13 (a rearrangement product of the cyclopropane chlorin 11) are observed as minor byproducts.200... 

How many different products that retain the three-membered ring are possible in the reaction of chlorine with cyclopropane Do any of the products exist as stereoisomers ... 

Much was unknown for the halogenation for unreactive substrates until very recently, when the biosynthesis of the cyclopropyl amino acid side chain of coronatine was elucidated. This intriguing pathway, which involves /-chlorination of an enzyme-bound L-isoleucine followed by chloride displacement by the a-carbon, yields the cyclopropanated precursor... 

With sulfur and triethylamine in dimethylformamide, compounds (86) give (89) (Equation (21)) <89JPR243>. With thiols or KjS, sulfides are produced (e.g., (90) and (91)), which show spasmolytic activity in vitro <86MI 404-01 >. Smooth 5N2-displacements of chlorine occur with phenol, thiophenol, SCN, and thiourea in dimethylsulfoxide. However, with K2CO3 or sodium cyanide, (86) (Ar = Ph) affords the trimers (92) or (93) (Scheme 32). With electron-deficient trans alkenes, stereoselective formation of cyclopropanes (94) was observed (Scheme 32). No reactions occur with maleates <66HCA412>. 

The overall sequence of cyclopropanation of a cyclic silyl enol ether, chlorination with FeCl3, and dehydrochlorination represents a very reliable one-carbon ring expansion method for cycloalkanomer (Table 11). 

The dichlorocarbene produced in this way in chloroform adds not only stereoselec-tively but also stereospedfically to olefins (Figure 3.11). Doubly chlorinated cyclopropanes are produced. These are not only of preparative interest as such, but they can also be used as starting materials for the synthesis of chlorine-free cyclopropanes. Chlorine can successfully be removed, for example, with Bu3SnH according to the mechanism discussed in Section 1.9.1 for bromides and iodides. Being able to prepare dichlorocarbene as conveniently as described makes the two-step process attractive for producing chlorine-free cyclopropanes. 

Another remarkable example of the solvent-influenced chemoselectivity of chlorine radicals is the photochlorination of cyclopropane to give, in competitive reactions, either 3-chloropropyl radicals (by Sh2 ring opening kc) or cyclopropyl radicals (by H abstraction h) as intermediates. The rate constant ratio kc/kn was found to increase by a factor of 372 on going from the gas phase to 1,2-dichloroethane, presumably as a result of the internal pressure of the solvents used. Thus, solvents of high internal pressure favour the Sh2 process, while H-abstraction becomes more important in the gas phase and in solvents of low internal pressure [826],... 

The additions of chlorofluorocarbene to (Z)- and ( )-but-2-ene were greater than 99% stereospecific. The isomer of cyclopropane is produced in excess in which chlorine is cis to the largest number of methyl groups. ... 

Preparation of chlorocyclopropane derivatives by substitution can be carried out with various reagents (Table 10). Differing acidic protons have been replaced by chlorine using base followed by addition of a chlorinating agent the reagents employed depend on the nature of the hydrogen to be substituted. Application of butyllithium followed by addition of tosyl chloride has been used to attach a chlorine atom to a number of cyclopropanes incorporated in polycyclic structures. Representative examples include tetracyclo[3.2.0.0 . 0 ]heptane and tetra-cyclo[4.1.0.0 . 0 ]heptane which were converted to l-chlorotetracyclo[3.2.0.0 . 0 ]heptane (1) and an isomeric mixture of trans- and cw-3-chlorotetracyclo[4.1.0.0. 0 ]heptane (2), respectively, in reasonable yield. 

Chlorination of liquid methylenecyclopropane with gaseous chlorine at 0°C yielded a mixture of 3-chloro-2-(chloromethyl)propene (2, 73%) and l-chloro-l-(chloromethyl)cyclopropane (1, 21%) An electrophilic attack of a chlorocation was assumed as 2,4-dichlorobut-l-ene, one of the major products of the photochlorination of methylenecyclopropane, was not formed. ... 

Various (a-chloroalkyl)cyclopropanes have been prepared by direct chlorination of the corresponding alkylcyclopropanes using /ert-butyl hypochlorite, ° chlorine, sul-furyl chloride,or jV-chlorosuccinimide " as chlorine source. A disadvantage is that when several positions in the substrate are available for attack and no directing group is present the product is obtained as a mixture of this renders the method... 

Formation of cyclopropane-containing oligocyclic systems such as nortricyclenes from nor-bornadienes also proceed via intramolecular insertion of homoallylmetal complexes. Palladated nortricyclene 19 can be converted with lithium aluminum hydride, chlorine or bromine to give 3-exo-methoxynortricyclene (20) and the en(/o-3-halo-exo-5-methoxy analogs 21 and 22, respectively. Intramolecular alkene insertion into the Pd — C bond is assumed to form the nortricyclene skeleton. ... 

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. 

Although cyclopropanes are far less reactive than alkenes, they can be opened by various electrophiles including protic acids, bromine, chlorine, mercury(II) salts and acetyl chloride. The ring-cleavage processes of cyclopropanes by electrophiles were studied with the aid of ab initio molecular orbital and other calculations. Early studies assumed that traditional... 

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