Organometallic compounds halogenations, bromine

Ketones can be a-brominated on solid phase by treatment with synthetic equivalents of bromine, such as pyridinium tribromide (Entry 2, Table 6.1) or phenyltri-methylammonium tribromide (DCM, 20 °C, 3 h [10]). Resin-bound organometallic compounds, such as vinylstannanes [11] or organozinc derivatives [12], react cleanly with iodine to yield the corresponding vinyl or alkyl iodides (see also Section 3.13). Additions of halogens or their synthetic equivalents to C=C double bonds on cross-... 

The C—I bond is very unstable and more reactive than C—Br, C—Cl and C—F bonds. Iodine is the most expensive of the common halogens and is much less frequently used in synthesis than bromine, chlorine or fluorine. Organometallic reactions proceed with iodinated aliphatic or aromatic compounds more easily than with the other halogens. Noble metal catalysis with palladium complexes is most effective with iodinated compounds. A useful synthetic procedure is the facile reduction of iodinated derivatives under mild conditions. Replacement of iodine by hydrogen at an sp carbon is an exothermic reaction with A// = -25 kJ mol . ... 

The stereodefined alkenyl halides are of prime importance due to the developments of di- or trisubstituted alkene synthesis by cross-coupling reactions between organometallics and alkenyl halides, catalyzed by transition metal compounds [1-4]. 1-Halo-l-alkenes are conveniently synthesized via hydrobo-ration-halogenation reaction [5]. However, with these methods it is not possible to synthesize 2-halo-1-alkenes. Although the halometalation reaction is considered to be a powerful tool for the synthesis of 2-halo-1-alkenes, the reaction has not been adequately developed for such purpose [6]. Lappert and coworkers [7-10] are perhaps the first to report the systematic haloboration reactions of unsaturated hydrocarbons with BX,. However, there is no systematic approach to the haloboration with B-X-9-BBN to organic synthesis [11]. The desired B-X-9-BBN is prepared [12] by the reaction of 9-BBN with phosphorous pentachlo-ride, bromine, or HI. Alternatively, B-X-9-BBN are very conveniently obtained... 

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