Dichloromethyl radical

Stereocontrolled radical cyclization to furansRadical cyclization of allyl 2-haloethyl ethers such as 1 show only slight stereoselectivity. However similar cyclization, but involving a dichloromethyl radical, can be highly cis-selective, whereas cyclization involving a monochloromethyl radical is frans-selective. The... 

The hypothesized transformation pathways of CT and CF to methane are shown in Figure 2. The transformation of CT and CF to methane in the Pd/alumina system, despite the low reactivity of MeCl, indicates that the reactions do not involve sequential dehalogenation of CF to methane (i.e. MeCl is not an intermediate). The formation of C2 and C3 compounds during the transformation of both CT and CF indicates the existence of a radical pathway. However, the production of ethane (12-14%) and CF (18-23%) from CT was much lower than that of methane (51-60%). This implies that the main transformation pathway is a direct reaction of CT to methane, with a secondary pathway involving a trichloromethyl radical which then reacts to form CF and C2 and C3 species. Similarly, the relatively low production of ethane (<1%) from CF indicates that the major pathway for the reaction of CF to ethane occurs through direct transformation to methane, rather than through a dichloromethyl radical species. (Lowry and Reinhard 1999)... 

J. Loss of a dichloromethyl radical from metastable ions ... 

The dichloromethyl radicals combine to give a vibrationally excited state of 1,1,2,2-tetrachloroethane [2186],... 

Dichloromethyl radical CCI2-H 83.8 2 350.6 8.4 Derived This volume... 

Several attempts were made to shift the regioselectivity towards the para-product. Phenols irradiated in chloroform are converted in the corresponding 2- and 4-substituted benzaldehydes by a mechanism involving attack by the dichloromethyl radical to produce... 

Anticipated products from the reaction of sym-dichloromethyl ether with ozone or OH radicals in the atmosphere, excluding the decomposition products formaldehyde and HCl, are chloromethyl formate and formyl chloride (Cupitt, 1980). 

Chlorination.1 C120 is particularly useful for side-chain chlorination of deactivated aromatic substrates by a free-radical process involving CIO . Although it cun be used to convert methylarenes to mono- and dichloromethyl derivatives, it is particularly useful for conversion to trichloromethylarenes. Thus it converts p-nitrotoluene into p-nitrobenzotrichloride in 99.8% yield. It is also useful for selective replacement of benzylic hydrogens. 

Liver is the principal site of chloroform metabolism which involves two major pathways, both of which are catalyzed by the cytochrome P-450 enzymes in the presence of NADPH. The oxidative pathway produces phosgene and the reductive pathway produces the dichloromethyl free radical. Other metabolites of chloroform include chloro-methanol, hydrochloric acid, hydrogen chloride, and digluathionyl dithiocarbonate, with carbon dioxide as the predominant end product of metabolism. 

Bunyan, P.J., and Cadogan, J.I.G., Reactivity of organophosphorus compounds. Part 13. Radical-chain transfer reactions of triethyl phosphite. A new phosphorothiolate synthesis, J. Chem. Soc., 2953, 1962. Elkaim, J.C., and Riess, J.G., Direct syntheses of (dichloromethyl)phosphonyl esters and amides. Tetrahedron Lett., 16, 4409, 1975. 

The treatment of diethyl (trichloromethyl)phosphonate with BuLi in thf affords diethyl [lithio(dichloromethyl)]-phosphonate the latter undergoes reactions with aldehydes or ketones to give, not only dichloroalkenes, C12C=CR R but also, from RCHO, the saturated esters RCH=CAB (A, B = Cl or P03Et2) The products from the interaction of the (l-haloalkyl)phosphonic diesters, (EtO)2P(0)CHXR (X = Cl, Br or I R = H or Me) and alk-1-enes, H2C=CHR (R = pentyl, OEt, OBu, OAc, CN or Ac) under free radical conditions, are mixtures containing moderate amounts of the esters 658 and 659, as well as diethyl methylphosphonate, in relative amounts which depend on reaction conditions " ... 

Tamao et al. have investigated (dichloromethyl)dimethylsilyl ethers as radical cyclization precursors [69]. Silyl ether 174 was readily prepared from the commercially available silyl chloride and isophorol. 5- xo-trig cyclization could be effected under high-dilution conditions, affording the bicycle 175 as a 6 4 mixture of stereoisomers. Subsequent oxidative tether cleavage afforded 2-formyl alcohols 176 and 177 where unfortunately, the presence of base caused partial epimerization of the center a to the formyl group (Scheme 10-56). 

Scheme 10-56 A (dichloromethyl)dimethylsilyl ether can be used as a formyl radical equivalent.

Scheme 10-57 Two radical cyclizations are possible with a (dichloromethyl)silyl ether tether.

The first synthesis of an (a-haloalkyl)boronic ester [8], a free radical addition of a tetrahalomethane, was followed by mechanistic studies that indicated the potential for stereospecific alkylation with Grignard reagents via borate intermediates [9], if only there had been a way to obtain asymmetric examples. The discovery of the efficient reaction of (dichloromethyl)lithium with boronic esters to form (a-chloroalkyl)boron-ic esters by insertion of a CHCl group into the B-C bond opened a new opportunity [10]. Boronic esters of pinanediol, prepared from (+)-a-pinene by osmium tetroxide catalyzed oxidation, were soon found to undergo the insertion reaction with a strong asymmetric bias, with diastereomeric selectivities frequently in the 90-95% range [llj. It was subsequently found that anhydrous zinc chloride promotes the reaction and increases diastereoselectivity to as high as 99.5% in some cases [12]. 

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