Electrochemical Reduction of 1,5‐Dihalopentanes at Carbon Cathodes in Dimethylformamide

Abstract

Studies of the electrochemical reduction of 1,5-dibromo-, 1,5-diiodo-, 1-bromo-5-chloro-, and 1-ch]oro-5-iodopentane at carbon electrodes in dimethylformamide containing tetramethylammonium perchlorate have been carried out with cyclic voltammetry and controlled-potential electrolysis. Cyclopentane, arising from the intramolecular cyclization of an electrogenerated 5-halopent-l-yl carbanion, is a significant electrolysis product. Moreover, depending on the identity of the 1,5-dihalopentane and the presence or absence of a proton source, one can obtain substantial yields of n-pentane, 1-pentene, 1-chloropentane, and 1,10-dichlorodecane as well as smaller amounts of cis-and trans-2-pentene, 5-chloro-1-pentene, 1,4-pentadiene, n-decane, 1-decene, n-pentadecane, 1-pentadecene, and n-eicosane. Experiments involving the use of several different deuterium ion or atom donors have been employed to determine the pathways by which these products are formed. In addition, we offer some comparisons concerning the electrochemical behavior of 1,3-dihalopropanes, 1,4-dihalobutanes, and 1,5-diha]opentanes at carbon cathodes.Only a limited amount of research concerning the electrochemistry of 1,5-dihalopentanes has been published, all of which pertains to the electrochemical reduction of 1,5-dibromopentane at mercury cathodes. 1-~ In a polarographic study of the reduction of 1,5-dibromopentane in dimethylformamide containing tetramethylammonium bromide and 5% water, Z~vada et al. 1 concluded that the starting material is reduced in a pair of two-electron steps which cannot be resolved into discrete waves. Rift 2'3 investigated the electrolytic reduction of 1,5-dibromopentane at a mercury pool in dimethylformamide containing tetra-n-butylammonium perehlorate and postulated that n-pentane is produced through a carbanion mechanism. However, different results were reported by Casanova and Rogers, ~ who found that controlled-potential electrolysis of 1,5-dibromopentane at mercury in dimethylformamide containing various tetraalkylammonium salts afforded a dialkylmercury species (CsHIoHgC~HI0) in high yield, whereas constant-current electrolysis of the same starting material gave only n-pentane. Avaca et al. ~ examined the electrochemical behavior of 1,5-dibromopentane in dimethyliormamide or acetonitrile containing various tetraalkylammonium salts at a mercury cathode and observed that controlled-potential eleetrolyses yielded mercury-containing solids with the general formula (C~HIoHg)~.In this paper we discuss the electrochemical reductions of 1,5-dibromo-, 1,5-diiodo-, l-bromo-5-ehloro-, and lchloro-5-iodopentane at carbon cathodes in dimethylformamide containing tetramethylammonium perehlorate; the electrochemistry of the last three 1,5-dihalopentanes has not been described previously. In performing this work, we have avoided the possible formation of organomercury compounds by not using mercury cathodes. We report for the first time the occurrence of electroreduetive intramolecular eyclization of each of the four 1,5-dihalopenfanes ...

Formation of 2-(3‘-Oxocyclohexyl)-2-cyclohexen-1-one via Reduction of 2-Cyclohexen-1-one with Electrogenerated Nickel(I) Salen

“…For the direct reduction of 2-cyclohexen-1-one, we observed a single irreversible wave with a peak potential of −1.24 V. As described in more detail in a previous paper, the reduction of nickel(II) salen is a reversible process, and the cathodic and anodic peak potentials for the nickel(II) salen−nickel(I) salen redox couple are −0.85 and −0.78 V, respectively. Direct reduction of each of the alkyl iodides involved in this work gives rise to a single irreversible wave that is attributable to cleavage of the carbon−iodine bond, and the pertinent peak potentials are as follows: iodoethane, −1.50 V; 1-iodopropane, −1.55 V; 1-iodobutane, −1.45 V; and 1-iodopentane, −1.42 V …”

Catalytic reduction of 1-iodooctane by nickel(I) salen electrogenerated at carbon cathodes in dimethylformamide: Effects of added proton donors and a mechanism involving both metal- and ligand-centered one-electron reduction of nickel(II) salen

“…Furthermore, although D 2 O must possess an acidity comparable to that of H 2 O (pK a = 31.7 in DMF [73,74]), which makes it an exceedingly poor proton (deuteron) donor in comparison with either HFIP or phenol, the use of D 2 O provides an excellent signature for the intermediacy of alkyl carbanions. Alkanes, which appear prominently among the products derived from direct electrochemical reduction of alkyl halides at carbon cathodes in the presence of 200-1000 mM D 2 O [62, [77][78][79][80], are usually monodeuterated to Table 1 Coulometric data and product distributions for catalytic reduction of 20 mM 1-iodooctane by 2.0 mM nickel(I) salen electrogenerated at reticulated vitreous carbon cathodes held at À1.00 V in DMF containing 0. 10 the extent of 40-50%.…”

Intramolecular reductive cyclisations using electrochemistry: development of environmentally friendly synthetic methodologies

“…The example of Scheme 34 illustrates the synthesis of spiropentane 67 from the electrolysis of 1,3-dibromo-2,2-bis (bromomethyl)propane 66 at a mercury cathode. 105 More recent work concerning the direct reduction of a,odihaloalkanes in DMF confirmed that, while the direct electrolyses of 1,3-dihalopropanes afforded cyclopropanes in high yields, 106 the direct reduction of higher 1,o-dihaloalkanes [107][108][109] gave the corresponding cyclic derivatives in very low yields. However, in the presence of electrogenerated Ni I (salen), 1,6-dibromohexane affords cyclohexane in up to 78% yield in DMF.…”