Dihaloalkanes preparation

Just as It IS possible to prepare alkenes by dehydrohalogenation of alkyl halides so may alkynes be prepared by a double dehydrohalogenation of dihaloalkanes The dihalide may be a geminal dihalide, one m which both halogens are on the same carbon or it may be a vicinal dihalide, one m which the halogens are on adjacent carbons... 

The malonic ester synthesis has been adapted to the preparation of cyclo alkanecarboxyhc acids from dihaloalkanes... 

In view of the ready availabiUty of optically pure lactic acid derivatives this reaction offers an attractive general method for the preparation of optically pure aromatic ester derivatives (41). Stereoselective alkylation (15—60% inversion) of ben2ene with optically active 1,2- 1,3- and 1,5-dihaloalkanes was also reported (42). 

This reaction gives fair-to-good yields of monoorganotin tribromides and trichlorides when quaternary ammonium or phosphonium catalysts are used (149). Better yields are obtained with organic bromides and staimous bromide than with the chlorides. This reaction is also catalyzed by tri alkyl antimony compounds at 100—160°C, bromides are more reactive than chlorides in this preparation (150,151). a,C0-Dihaloalkanes also react in good yield giving CO-haloalkyltin trihaHdes when catalyzed by organoantimony compounds (152). 

The first reported electroorganic synthesis of a sizeable amount of material at a modified electrode, in 1982, was the reduction of 1,2-dihaloalkanes at p-nitrostyrene coated platinum electrodes to give alkenes. The preparation of stilbene was conducted on a 20 pmol scale with reported turnover numbers approaching 1 x 10. The idea of mediated electrochemistry has more frequently been pursued for inorganic electrode reactions, notably the reduction of oxygen which is of eminent importance for fuel cell cathodes Almost 20 contributions on oxygen reduction at modified... 

Gusarova, N.K., Shaikhudinova, S.I., Dmitriev, V.I., Malysheva, S.F., Arbuzova, S.N., and Trofimov, B.A., Reaction of red phosphorus with electrophiles in superbasic systems. VII. Phospholanes and phosphorinanes from red phosphorus and a,co-dihaloalkanes in a single preparative step, Zhur. Obshch. Khim., 65, 1096, 1995. 

Several syntheses of l,3-dioxoperhydropyrrolo[l,2-c]imidazoles have been developed using different strategies. a-Substituted bicyclic proline hydantoins were prepared by alkylation of aldimines 135 of resin-bound amino acids with a,tu-dihaloalkanes and intramolecular displacement of the halide to generate cr-substituted prolines 136 and homologs (Scheme 18). After formation of resin-bound ureas 137 by reaction of these sterically hindered secondary amines with isocyanates, base-catalyzed cyclization/cleavage yielded the desired hydantoin products <2005TL3131>. 

Alkynes have been prepared from 1,1- and 1,2-dihaloalkanes and from haloalkenes under the influence of a quaternary ammonium salt geminal- and vic-dibromoalkanes are converted into alkynes under liquid liquid [10, 11] and soliddiquid [12-14] conditions with Aliquat or tetra-n-octylammonium bromide... 

Ethylenimines may also be prepared by the reaction of 1,2-dihaloalkanes with amines or ammonia. For example, ethylenimine may be prepared in the laboratory or on an industrial scale by the reaction of ethylene dichloride with ammonia [42]. The reaction of amines with a,/3-dibromo ketones yields imines as described in Eq. (18) [43]. 

In general, the preparation of gem-dizincioalkane via the treatment of 1,1-dihaloalkane with zinc is more difficult than the preparation of gewt-dizinciomethane. The reduction of gem-dihaloalkanes carrying fi-hydrogens may suffer from /J-hydride elimination and result in the formation of alkenes. In addition, depending on the substrate, the intermediary a-haloalkylzinc compound is less stable than a-halomethylzinc towards the a-elimination (Scheme 2). 

In the above procedures, the preparation of 1,1 -dihaloalkanes is indispensable, but it often contains some synthetic difficulties. Several efficient methods have been reported for their preparations. Halogen-exchange reaction is one of the most commonly used (Scheme 3)20. Selective reduction of 1,1-dihaloalkene with diazene also gives 1,1-dihaloalkane21. 

As described in Section II, the preparation of 1,1-dizincioalkane can be achieved not only by reduction of 1,1-dihaloalkane, but also by allylzincation of alkenyl metal compounds. The reaction of allylzinc with alkenyl Grignard reagent, which is followed by the addition of aldehydes, gives dienes as shown in Scheme 1511,41. 

Extremely shock-sensitive alkylene bis[5-thiatriazolyl]sulfides were prepared by Pilgram et al.44 45 by treating sodium thiatriazole-5-thiolate with dihaloalkane. Dichloromaleimide reacted analogously.45... 

Oligo- and polymethylene-bridged complexes can be prepared by reaction of metal carbonyl anions with w.w -dihaloalkanes. This method proved to be a simple entry to the iron series /j,-(CH2)j.][(t75-C5H5) Fe(CO)2]2 (x s 3) (283), but yielded quite different products in the case of Na[(T 5-C5H5)Mo(CO)3] (283) and Na[Mn(CO)s] (284). An alternative two-step synthesis of the iron compounds involves the preparation of the mononuclear w-haloalkyls LXM—(CH2)X—X, and a subsequent... 

Quite a large number of these are known and they may be prepared from the dihaloalkane and lithium dialkyl- or diphenyl-stibide in THF at low temperature, or from the sodium stibide in liquid ammonia. 

In the preparation of pyrroles and N-vinylpyrroles from ketoximes, along with vinyl halides, dihaloalkanes as acetylene equivalents can also be used. Pyrroles and /V-vinylpyrroles are formed in a yield of about 30% in the reaction of ketoximes with dihaloalkanes in the presence of excess alkali metal hydroxide in DMSO (Scheme 60) (79IZV2840). 

Nickelapentacycles have also been prepared by the reaction of 1,4-dihaloalkanes such as 1,4-dibromobutane or 1,4-dibromopentane with Ni(COD)(bipy) (bipy = 2,2 -bipyridyl) to afford complexes of type 71 as dark green crystalline... 

Alkynes can be prepared from dihaloalkanes by elimination of two molecules of HX. This reaction requires very strongly basic conditions so potassium hydroxide at elevated temperatures or the stronger base sodium amide (NaNH2) is commonly employed. Examples are provided by the following equations ... 

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