Dimethylboron bromide

These reaction conditions do not affect most of the other common hydroxy-protecting groups and the methoxybenzyl group is therefore useful in synthetic sequences that require selective deprotection of different hydroxy groups. 4-Methoxybenzyl ethers can also be selectively cleaved by dimethylboron bromide.182... 

Allenyldibromoborane was obtained in 34% yield by the reaction of boron tribromide with allenyltributylstannane below -80 °C [28], Allenyldimethylborane was likewise prepared in 84% yield from dimethylboron bromide. In neither case was the propargylborane observed. Both allenylboranes react with acetone to yield 2-methyl-4-pentyn-2-ol after hydrolysis (Eq. 9.25). 

Dimethylboron bromide is also a regioselective reagent for the opening of cyclic ethers1112. B-bromobis(dimethylamino)borane is a less selective reagent1113. 

The next step was the introduction of the methylene acetal residue in 6 and 7 (Scheme 5). The initial plan was to effect this transformation in a single step, by exposure of the methoxymethyl derivatives 6 and 7 to dimethylboron bromide, following the conditions developed by Roush and co-workers (38). However, this reaction was not successful for either substrate, presumably due to competing cleavage of the acetonide residue. More promising results were obtained with triol 29 (obtainable from controlled hydrolysis of 7). Thus,... 

Deoxygenation of sulfoxidesf Dimethylboron bromide and 9-borabicy-clo[3.3. IJnonyl bromide (Aldrich) convert alkyl and aryl sulfoxides to sulfides at low temperature and in high yield. 

Acetals N-Bromosuccinimide. f-Bulyl hydroperoxide. Dimethylboron bromide. Na-fion-H. Organocopper reagents. Organoti-tanium reagents. Titanium(IV) chloride. 

The remaining MOM ether in intermediate 32 is cleaved by treatment with dimethylboron bromide in CH2CI2 at -78 °C to provide deoxylaulimalide 32 in 98 % yield. This sequence demonstrates the orthogonality of MOM ether and the 4-oxopent-2-yl group, even under acidic conditions. No 2,3- /Z-isomerization occurred during this deprotection step. 

Lastly in this section dimethylboron bromide has been reported as a useful catalyst of thiol-alcohol exchange for the... 

Conversion of MEM-protected alcohols to related cyanomethyl ethers by use of dimethylboron bromide in dichloromethane at low temperature, followed by addition of cyanide, has also been reported. 

An attractive feature of the MEM group is the ease with which it can be removed under nonaqueous conditions. Lewis acids such as zinc bromide, titanium tetrachloride, dimethylboron bromide, or trimethylsilyl iodide permit its removal. The MEM group is cleaved in preference to the MOM or THP groups under these conditions. Conversely, the MEM group is more stable to acidic aqueous hydrolysis than the THP group. These relative reactivity relationships allow the THP and MEM groups to be used in a complementary fashion when two hydroxyl groups must be deprotected at different points in a synthetic sequence. 

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