4.4- dihalo-2- -3- alkanal

Total reduction of unbranched open-chain and cyclic derivatives of dichloro and dibromo alkanes occurs at room temperature within 30 minutes in dichloro-methane solutions containing ca. 2.5 equivalents of triethylsilane and ca. 0.25 equivalents of aluminum chloride.189 The reaction occurs equally well with geminal, vicinal, and m-dihalo alkanes. For example, 1,5-dibromopentane gives n-pen lane in 85% yield when treated in this way (Eq. 53).189... 

An efficient synthesis of thietanes (29) via reaction of 1,3-dihalo alkanes (28) with sodium sulfide was recently reported by Lancaster and Smith.S7... 

The method of greatest applicability is the reaction of alkali metal phosphides with dihalo-alkanes, -alkenes, etc. (equation 4). Generally this reaction proceeds well and in high yield excess dihaloalkane should be avoided as this leads to the production of phosphonium salts which can contaminate the product. 

The cleavage of tetrahydrofuran and its alkylated derivatives with halogen acids is an excellent method for the preparation of, A-dihalo-alkanes.The reaction of tetrahydrofuran with the less-reactive hydrogen chloride stops at the chlorohydrin stage, whereas the reaction in the presence of zinc chloride catalyst leads to the formation of the dichloride. The crude reaction mixture containing the intermediate chlorohydrin may be treated directly with phosphorus tribromide, yielding tetramethylene chlorobromide. The preparation of dibromides can be accomplished easily with hydrogen bromide or phosphorus and bromine and diiodides, by the action of potassium iodide and orthophosphoric acid. ... 

Electrophilic sulfur mustards formed from conjugation with vicinal dihalo alkanes. 

With a,/S-dihalo alkanes and formation of thiazolidine-2-thiones. . 619... 

With a./5-dihalo alkanes and formation of perhydro-l,3,4-thiadi-... 

Method A 2-amino alcohol and CS, (Section IIj). Bj 2-halo amine and CSj (Section TVj), B 2-sulfato amine and CSj (Section IVj). C ethyleneimine unsaturated amines) and CSj (Section IVj). D 2-amino thioles and CSj (Section III,). E 2-iminothiazolidines and CSj (Section HI,). F jS,y-unsaturated amine and CSj (Section IVJ. G amines, CSj and a-halo ketones (Section IV,), H amines, CSj and 1,2-dihalo alkanes (Section VIg). 

Since thiazolidine-2-thiones (LX) can be readily prepared from 2-halo amines and carbon disulfide (Section IV.t), it is, in principle, possible to prepare these substances from a dithiocarbamic acid (CLXXXVI) and a 1,2-dihalo alkane (method H, Table 21). 

Monohalo or dihalo alkanes, carboxylic acids, or ketones are obtained on treating diazoalkanes,1167 diazocarboxylic esters,1168 or diazo ketones with hydrogen halides or halogens. The reaction usually occurs at room temperature or below. However, preparative importance attaches only to the formation of the halo ketones from diazo ketones they are obtained free from isomers (cf. page 189). 

This involves an intramolecular reaction. Thus, piperidines are also formed by cyclizing 1,5-dihalo-alkanes with primary amines. 

Adsorption of Halides on Aluminium. Very recently the adsorption of iodoal-kanes [18] as well as of 1,3-dihalo-alkanes [19] on Al(lOO) and Al(lll) surfaces was studied. 

Carbanions formed from methyl methylthiomethyl sulfoxide 94 and ethyl ethylthio-methyl sulfoxide 95 were shown to be alkylated in excellent yields126,127. Treatment of 94 with rc-BuLi or KH and subsequent reaction with 1, n-dihalo- or bis(tosyloxy)alkane gave 3-, 4-, 5- and 6-membered 1-methylsulfmyl-l-methylthiocycloalkanes128"130. Upon hydrolyses of these products, the corresponding aldehydes and ketones are obtained. 

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