HYDROBORATION .52. MONOHALOBORANE METHYL SULFIDE ADDUCTS AS NEW REAGENTS FOR THE HYDROBORATION OF ALKENES - CONVENIENT SYNTHESIS OF DIALKYLHALOBORANES AND THEIR DERIVATIVES FOR ORGANIC-SYNTHESIS

Reactions of alkenes with the recently discovered monochloroborane-methyl sulfide (H2BCl-SMe2, monobromoborane-methyl sulfide (H2BBr-SMe2, and monoiodoborane-methyl sulfide (H2BI-SMe2were investigated in detail in order to establish their usefulness as hydroborating agents. H2BCl-SMe2hydroborates alkenes rapidly and quantitatively at 25 °C. Simple distillation under low pressure affords pure RjBCl. Similarly, the hydroboration of alkenes with H2BBr-SMe2followed by distillation affords pure R2BBr in the case of hindered alky! groups and the corresponding methyl sulfide complexes in the case of unhindered alkyl groups. Distillation of R2BBr-SMe2following the addition of 1 mol equiv of BBr3gives pure R2BBr. The reactions of H2BI-SMe2are slower, but it reacts satisfactorily with alkenes in refluxing dichloromethane. Distillation affords dialkyliodoboranes almost free from SMe2. These dialkylhaloboranes are readily converted into other dialkylboron derivatives by treatment with appropriate reagents. Such derivatives are useful as intermediates in organic synthesis. © 1979, American Chemical Society. All rights reserved.