Acetonides cleaved

Cyclop entylidene are slightly easier to cleave than acetonides... 

Me3SiBr, CH2CI2, 0°, 8-9 h, 80-97% yield.This reagent also cleaves the acetonide, THP, trityl, and r-BuMe2Si groups. Esters, methyl and benzyl ethers, r-butyldiphenylsilyl ethers, and amides are reported to be stable. 

NCSBu2Sn)20 1%, THF, H20. Acetonides and TMS ethers are also cleaved under these conditions, but TBDMS, MTM, and MOM groups are stable. This catalyst has also been used to effect transesterifications. ... 

Dichlorodicyanoquinone (DDQ), CH2CI2, H2O, 40 min, it, 84-93% yield.This method does not cleave simple benzyl ethers. This method was found effective in the presence of a boronate. The following groups are stable to these conditions ketones, epoxides, alkenes, acetonides, to-sylates, MOM ethers, THP ethers, acetates, benzyloxymethyl (BOM) ethers, and TBDMS ethers. 

TsOH, MeOH, 25°, 5 h. These conditions failed to cleave the acetonide of a 2, 3 -ribonucleoside. ... 

In the following example the acetonide protective group is selectively converted to one of two t-butyl groups. The reaction appears to be general, but the alcohol bearing the t-butyl group varies with structure.Benzyli-dene ketals are also cleaved. 

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. 

I2, MeOH, reflux, 2 h, 79% HCIO4, H2O, 25°, 16 h, 87% yield. These conditions also cleave acetonides and benzylidene acetals. ... 

Acetonides are quite stable to base, and to oxidation, dehydration and acylation reactions carried out in pyridine. They are cleaved by acid hydrolysis. The 17,21-acetonides of 17a,21-dihydroxy-20-keto steroids and related acetals are split by very mild acid conditions. ... 

Acetonides of 21-hydroxy- and 21-desoxy-20-ketones and related acetals are often stable to dilute boiling mineral acid " but in certain instances, acetonides are cleaved in modest yield by 0,5 A hydrochloric acid in... 

A nitrophenylsulfenate, cleaved by nucleophiles under very mild conditions, was developed as protection for a hydroxyl group during solid-phase nucleotide synthesis. The sulfenate ester is stable to the acidic hydrolysis of acetonides. ... 

The rather unusual conversion of an acetonide to an isopropenyl ether was developed to differentiate a terminal acetonide from several internal ones. The isopropenyl ether was in turn converted to the 1-methylcyclopropyl ether, which was later cleaved with NBS or DDQ. ... 

Me2BBr, TEA, BH3-THF, —78° warm to —20° over 1 h, 70-97% yield. These conditions cleave the benzylidene acetal, to leave the least hindered alcohol as a free hydroxyl. If diborane is omitted from the reaction mixture and the reaction is quenched with PhSH and TEA, the benzylidene group is cleaved to give an (9,5 -acetal [ROCH(SPh)Ph]. Acetonides are cleaved similarly." ... 

BH3 SMe2, CH2CI2, 0°, 1 h, then BF3, 5 min. Simple benzylidene acetals are cleaved efficiently without hydroboration of alkenes that may be present, and acetonides are converted to the hydroxy isopropyl ethers. 

BH2CI-DMS, toluene, reflux, 95% yield. Acetonides and THP ethers are cleaved, and epoxides are converted to the chlorohydrin." ... 

For in = 2, 3) H5IO5, ether, THF, 77-99% yield. This method also cleaves oxathioacetals, but did not affect the acid-sensitive acetonide or 1,3-diox-olane. Note that ethereal periodic acid has been used to cleave terminal acetonides with subsequent glycol cleavage. ... 

NaN02, 1 N HCl, CH3OH, H2O, 0°, 3 h, 76% yield. In the last step of a synthesis of erythronolide A, acid-catalyzed hydrolysis of an acetonide failed because the carbonyl-containing precursor was unstable to acidic hydrolysis (3% MeOH, HCl, 0°, 30 min, conditions developed for the synthesis of erythronolide B). Consequently, the carbonyl group was protected as an oxime, the acetonide was cleaved, and the carbonyl group was regenerated. 

Cp2Zr, then water, 66% yield.O-Allyl ethers are cleaved at a faster rate THP, acetonide. Bn ethers, and benzoates are stable. 

The C2-symmetric epoxide 23 (Scheme 7) reacts smoothly with carbon nucleophiles. For example, treatment of 23 with lithium dimethylcuprate proceeds with inversion of configuration, resulting in the formation of alcohol 28. An important consequence of the C2 symmetry of 23 is that the attack of the organometallic reagent upon either one of the two epoxide carbons produces the same product. After simultaneous hydrogenolysis of the two benzyl ethers in 28, protection of the 1,2-diol as an acetonide ring can be easily achieved by the use of 2,2-dimethoxypropane and camphor-sulfonic acid (CSA). It is necessary to briefly expose the crude product from the latter reaction to methanol and CSA so that the mixed acyclic ketal can be cleaved (see 29—>30). Oxidation of alcohol 30 with pyridinium chlorochromate (PCC) provides alde-... 

Treatment of the elimination product 107 with triethylamine resulted in smooth isomerization of the olefin, to afford the a,p-unsaturated ketone 108. Ally lie oxidation of 108 then generated the secondary alcohol 109 in 72 % yield. The acetonide and silyl ether functions of 109 were cleaved in one reaction to afford a tetraol intermediate that was regioselectively acylated at the secondary alcohol functions, to provide the triacetate 110 in high yield (89 %). Hydrogenolysis of the benzyl ether... 

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