Monoprotection

Monoprotection of a symmetrical diol can be effected by reaction with a polymer-supported phenylacetyl chloride. The free hydroxyl group is then converted to an ether and the phenylacetate cleaved by aqueous ammonia-dioxane, 48 h. ... 

BuLi, BzCl, 10% Nh2C03, H2O, 82% yield.These conditions were used to monoprotect 1,4-butanediol. 

A variety of cyclic ortho esters,including cyclic orthoformates, have been developed to protect czs-1,2-diols. Cyclic ortho esters are more readily cleaved by acidic hydrolysis (e.g., by a phosphate buffer, pH 4.5-7.5, or by 0.005-0.05 M HCl) than are acetonides. Careful hydrolysis or reduction can be used to prepare selectively monoprotected diol derivatives. 

MONOPROTECTION OF DICARBONYL COMPOUNDS Selective Protection of a- and /3-Diketones... 

Cyclohexane-1,2-dione reacts with ethylene glycol (TsOH, benzene, 6 h) to form the diprotected compound. Monoprotected 1,3-oxathiolanes and 1,3-dithiolanes are isolated on reaction under similar conditions with 2-mercaptoethanol and eth-anedithiol, respectively. ... 

Coxon and Stoddart have directed their attention to the formation of penta-erythritol-derived cryptands. With these molecules, the strategy was to block one pair of hydroxyl groups as an acetal and form a crown from the remaining diol. In the first of the two reports cited above, this was accomplished by treating the 0-benzylidine derivative of pentaerythritol with base and diethylene glycol ditosylate. The crown was then treated with a mixture of UAIH4 and BF3 which gives partial reduction of the acetal as shown in (8.9), above. The monoprotected diol could now be treated in a fashion similar to that previously described and the benzyloxy cryptand (77) would result. The scheme is illustrated below as Eq. (8.10). 

DMSO, molybdenum peroxide, benzene, reflux, 7-20 h, -60% yield. This method was used to monoprotect 1,2-diols. The method is not general, because oxidation to a-hydroxy ketones and diketones occurs with some substrates. Based on the mechanism and on the results, it would appear that overoxidation has a strong conformational dependence. 

Dihydropyran, Dowex 50wx2, toluene, 10-355 min, 78-95% yield. These conditions were developed to monoprotect symmetrical l,m-diols. ... 

The authors prepared a number of substituted 2-diazomethylene derivatives of picolyl oxide to use for monoprotection of the cw-glycol system in nucleosides. The 3-methyl derivative proved most satisfactory. ... 

Bu3Sn)20 BzCl. The use of microwaves accelerates this reaction. Bu2Sn(OMe)2 is reported to work better than Bu2SnO in the monoprotection of diols. The monoprotection of diols at the more hindered position can be accomplished through the stannylene if the reaction is quenched with PhMe2SiCl (45-77% yield).Microwave heating has been found to be effective for this transformation in some cases. ... 

As with the benzylidene ketals, the carbonate can be opened to give a monoprotected diol. ... 

The TBDPS ether has been used for the monoprotection of a catechol (TBDPSCl, Im, DMF, 5 h, 83% yield) or simple phenol protection. It is cleaved with Bu4N F- (THF, 94% yield). ... 

Methyiaiuminum Bis(2,6-di-f-butyi-4-methyiphenoxide) Compiex, 364 MONOPROTECTION OF DICARBONYL COMPOUNDS... 

This ester was designed as a base-labile protective group. Monoprotection of aspartic acid was achieved using the DCC/DMAP protocol. Cleavage is... 

In many cases, a thiol group is introduced into a substrate through the use of a thiol (e.g., monoprotected H2S), by a simple displacement or an addition reaction. ... 

In an amine bearing two BOC groups, 2 eq. of TFA in CH2CI2 will cleave only one BOC, leaving a monoprotected primary cunine. ... 

For monoprotection of a phosphonic acid NCCH2CH2OH, CI3CCN, 74-93% yield. ... 

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