Cleavage tetrahydropyranyl esters

The Sc(OTf)3/ionic liquid system could also be utilized in chemoselective thioac-etalization and transthioacetalization of carbonyl compounds [79]. On the other hand, deprotection of tetrahydropyranyl or methoxymethyl ethers [80], tert-butyl amides [81, 82], debenzylation and cleavage of esters [83, 84] also proceeded well using scandium catalysts. 

Our final example is a base-labile 4-(phenylsulfonyl)methyl-l,3-dioxolane protecting group for aldehydes and ketones.4 Protection is carried out by the reaction of diol 17,1 (obtained by dihydroxylation of ally phenyl sulfone) with a carbonyl compound in the presence of pyridinium p-toluene sulfonate [Scheme 2.17], Cleavage is accomplished by treatment with DBU. /erf-Butyldimethylsilyl ethers, p-toluenesulfonate esters, tetrahydropyranyl ethers, carboxylic esters and benzoates are well tolerated. A disadvantage to the use of 17.1 is the introduc-... 

Recent methods for the cleavage of allyl ethers that have that have yet to be tested on the anvil of complex target synthesis include (a) diborane generated in situ by reaction of sodium borohydride with iodine in THF at 0 °C (cyanoT ester, nitro, acetonide and tetrahydropyranyl groups survive) 434 (b) cerium(Ill) chloride and sodium iodide in refluxing acetonitrile (benzyl. THP and Boc groups survive) 435 (c) iodotrimethylsilane in acetonitrile at room temperature 436 and (d) DDO in wet dichloromethane (secondary allyl ethers, benzyl, acetate and TBS groups survive).437... 

To use diastereomer [38] of [37] for synthesis of [41], a different sequence was required. As for [37], ester [38] was first converted to the tetrahydropyranyl ether [41]. The stereochemistry was corrected by esterification aiui THP cleavage to give benzoate [42], in the same stereo-... 

Tetrahydropyranyl ethers (I, unsymmetrical acetals) are oxidized exclusively to the hydroxy ester (2) on heating, this is converted into 6-valerolactone (3) with liberation of the alcohol. The reaction thus constitutes a useful method for cleavage of tetrahydropyranyl ethers under neutral conditions. 

Protection and deprotection. CuClj catalyzes tetrahydropyranylation of alcohols," as well as cleavage of phenacyl esters." In the latter process, oxygen is introduced into the refluxing medium (aqueous DMF). 

Tetrahydropyranyl (THP) ethers are frequently used as a protecting group for the hydroxyl group. Their formation and cleavage from alcohols and phenols have been successfully catalyzed by Bi(N03)3 5H20 [92] and Bi(0Tf)3 %H20 [93]. The conversion of THP ethers to acetate and formate esters has been reported to be efficiently catalyzed by Bi(0Tf)3 xH20 [94]. 

Zhou et al. [177] use a random copolymer of tetrahydropyranyl methacrylate (THPMA) and methyl methacrylate (MMA) polymer doped with BSB-S2 as the PAG for microfabrication. At the laser focal spot, the THPMA groups were converted to carboxylic acid groups due to photogenerated acid-induced ester cleavage reactions, and were therefore rendered soluble in aqueous base developer. Figure 45 shows the 3D microstructure produced by this method. By two-photon fluorescence imaging, it was found that the buried channels are open and a continuous connection was made between the two cavities. 

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