Benzyloxymethyl group alcohol protection

Alcohol Protecting Group. The foremost use for this reagent is as a protecting group for the alcohol functional group. This can be illustrated in a step utilized in the total synthesis of kijanolide (eq 1). An enantioselective synthesis of the taxol side chain used the benzyloxymethyl (BOM) ether for protection of an alcohol group (eq 2). ... 

From intermediate 12, the path to key intermediate 7 is straightforward. Reductive removal of the benzyloxymethyl protecting group in 12 with lithium metal in liquid ammonia provides diol 27 in an overall yield of 70% from 14. Simultaneous protection of the vicinal hydroxyl groups in 27 in the form of a cyclopentanone ketal is accompanied by cleavage of the tert-butyldimethylsilyl ether. Treatment of the resultant primary alcohol with /V-bromosuccini-mide (NBS) arid triphenylphopshine accomplishes the formation of bromide 7, the central fragment of monensin, in 71 % yield from 27. 

Acyclic 0,0-acetals are used for the temporary protection of mono-alcohols. Most commonly used are the tetrahydropyranyl (THP), the methoxymethyl (MOM), the benzyloxymethyl (BOM), or the methoxyethoxymethyl (MEM) protecting groups. 

A new and direct synthesis of (Z)-trisubstituted allylic alcohols has appeared [equation (13)] involving a lithium-free Wittig reaction of unstabilized phosphor anes with acyclic a-alkoxyketones Z.E ratios are best for R = 2-tetrahydropyranyl but, where steric hindrance at the carbon atoms to be joined makes reaction sluggish, the less bulky benzyloxymethyl protecting group may be preferable. 

In our efforts, we found that ethers other than methyl transfer efficiently as long as steric or electronic differences were insignificant. In fact, benzyloxymethyl substrates 57, readily prepared from protection of homoallylic alcohols with commercially available BOMCl, underwent efficient benzyl ether transfer (Scheme 37.16). This process significantly expands the scope of the reaction because, in contrast to methyl ethers, benzyl groups can be easily cleaved by hydrogenolysis. Thus, the ether transfer can provide access to orthogonally protected iy -l,3-diol units. 

---