Cyclopropanes, 1,1-dihalo-, formation

Cyclohexanone pyridylhydrazones, cyc-lization of, 91, 92, 94 Cyclopropanes, 1,1-dihalo-, formation of, 61... 

The intramolecular Wurtz-type coupling of dihaloorganic compounds with use of metallic zinc is a classical synthetic route to cyclic compounds. For example, cyclopropane derivatives can be prepared from 1,3-dihalo-propanes (29, 189a, 248, 451), and cyclobutane derivatives from 1,4-dihalobutanes (71). These reactions presumably proceed via the intermediate formation of organozinc compounds. The reaction of diethylzinc with esters of a,a -dibrominated aliphatic dicarboxylic acids leads to the... 

There are only two examples for the conversion of allyl halides to nonheteroatom-substituted vinylcyclopropanes. Firstly, vinyl- and (2-chlorovinyl)cyclopropanes can be prepared in yields of 18-77% by oxidative addition of a 3,3-dihalo-l-alkene onto a low-valent metal, e.g. Cu(0), thus forming a carbenoid which either reacts directly or after formation of the carbene with an alkene (see Houben-Weyl, Vol. E19b, pp673-674). ... 

A copper-containing oxocarbenoid is assumed to be involved in the formation of both the cyclopropanes 9 and the 4,5-dihydrofurans 10. It is therefore not surprising that the formal cyclotrimers of oxocarbenes, triacylcyclopropanes 12, were obtained in the absence of suitable reagents that could trap the oxocarbenoid. Cyclopropanes 12 are likely to be formed via the formal oxocarbene dimers 11, which in some cases are also found among the reaction products. In addition to the copper-mediated debromination of a,a-dibromo ketones, triacylcyclopropanes can also be obtained from a,a-dihalo ketones by metal-induced a-elimination in other cases, e.g. from a,a-dibromo ketones with Ni(0), Fe(0), or Co(0) complexes,", and from a,a-dichloro ketones with a zinc-copper couple. 

Formation of al icy die hydrocarbons by the action of sodium (Freund reaction) or zinc (Gustavson reaction) on open chain dihalo compounds 1,3-dichloropropane derived from the chlorination of propane obtained from natural gas is cyclized in the Hass cyclopropane process by treating with zinc dust in aqueous alcohol in the presence of catalytic sodium iodide ... 

Formation of cyclopropane derivatives by reaction between an a,/ -dihalo compound and an acidic methylene compound can, in principle, be initiated by direct cathodic formation of the anion... 

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