Dichloroborane-dimethyl sulfide

If alkyldichloroboranes are specifically required, dichloroborane-dimethyl sulfide is the reagent of choice. It is more stable and more convenient than the dichloroborane-diethyl ether complex, but its hydroborating properties are very similar." Dichloroborane complexes ethers even more strongly than monochloroborane, and its reactions with alkenes in this solvent are slow and lead to mixtures. Therefore, it is generally used in pentane and trichloroborane is added to liberate uncomplexed dichloroborane. Under these conditions it readily gives alkyldichloroboranes on reaction with alkenes or alkenyldichloro-boranes on reaction with alkynes. " " The latter reaction has been applied to alkynylsilanes (equation 44)." ... 

Monochioroborane-Dimethyl sulfide, H2BCI-S(CH3)2 Dichloroborane-Dimethyl sulfide, HBCI2 S(CH3)2. These stable hydroborating agents are prepared from borane-dimethyl sulfide (4, 124, 191 5, 47) and boron trichloride dimethyl sulfide (equations I and II). They possess the advantage over chloroborane etherates of indefinite stability. They show regiospecificity comparable to the... 

Hydroboration. This reagent, in contrast to dichloroborane-dimethyl sulfide, hydroborates alVenes directly without necessity for an added Lewis acid such as BCI3. Actually HBBr2 - S(CH3)2 would be expected to be less reactive than HBCl2 S(CH3)3, since it should be more acidic. Irrespective of the theoretical interpretation of the unexpected activity, hydroboration with this reagent leads to synthesis of the previously unknown alkyldibromoboranes, obtained as the S(CH3>2 addition compounds. These complexes can be freed from dimethyl sulfide by distillation in the presence of BBrs. The directive effects are similar to those observed with other borane reagents. 

Hydroboration of Alkenes and Alkynes. The hydroboration of alkenes with dichloroborane-dimethyl sulfide (DCBS) in refluxing dichloromethane produces considerable quantities of R2BCI and R3B as impurities, presumably as the result of disproportionation of the reagent. The addition of boron trichloride liberates dichloroborane and the hydroboration proceeds cleanly at25°C (eq 1). ... 

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