Borane-1,4-thioxane

Borane—dimethyl sulfide complex (BMS) (2) is free of these inconveniences. The complex is a pure 1 1 adduct, ca 10 Af in BH, stable indefinitely at room temperature and soluble in ethers, dichioromethane, benzene, and other solvents (56,57). Its disadvantage is the unpleasant smell of dimethyl sulfide, which is volatile and water insoluble. Borane—1,4-thioxane complex (3), which is also a pure 1 1 adduct, ca 8 Af in BH, shows solubiUty characteristics similar to BMS (58). 1,4-Thioxane [15980-15-1] is slightly soluble in water and can be separated from the hydroboration products by extraction into water. 

General Reactions.- Borane-1,4-thioxane hydroborated alkenes rapidly, and was used to prqKire synthetically useful monoalkyl- or dialkylboranes the 1,4-thioxane byproduct did not interfm-e with with the subsequrat utilisation of these reagents. The addition of catecholbor-ane to 2-substituted l-buten-3-ynes was catalysed by phosphine palladium(0) complexes the... 

Borane complexes, borane-THF and borane dimethylsulfide, are generally the appropriate reducing agents in this reaction. Borane thioxane has been used, but it suffers from the inconvenience that thioxane is quite expensive. Diborane gas has been tried by Callery and has proved to be very efficient. The use of this reagent could open new industrial developments for this technology. Catecholborane has shown some advantages at low temperature when selectivity is needed.40... 

Borane-dimethyl sulfide is a particularly useful reagent. The complex is more stable than borane-THF and can be prepared in neat form. It is soluble in a range of organic solvents and retains sufficient looseness to allow it to react readily with alkenes. It carries out most of the reactions of borane-THF, perhaps somewhat more slowly, and gives the same selectivity almost irrespective of solvent. It has been used to hydroborate alkynylsilanes at the a-position. Borane-thioxane is an alternative to borane-dimethyl sulfide. °... 

For the oxazaboroHdine-catalyzed reduction of prochiral ketones various borane reductants are employed. Borane-tetrahydrofuran and borane-dimethyl sulfide are the most frequently used reductants. Borane-l,4-thioxane [34], dibo-rane, catecholborane [35, 36, 37, 38], and diethylanihne-borane [39] are also useful borane reductants in this reduction system. 

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