THP ether

The oxidation of higher alkenes in organic solvents proceeds under almost neutral conditions, and hence many functional groups such as ester or lac-tone[26,56-59], sulfonate[60], aldehyde[61-63], acetal[60], MOM ether[64], car-bobenzoxy[65], /-allylic alcohol[66], bromide[67,68], tertiary amine[69], and phenylselenide[70] can be tolerated. Partial hydrolysis of THP ether[71] and silyl ethers under certain conditions was reported. Alcohols are oxidized with Pd(II)[72-74] but the oxidation is slower than the oxidation of terminal alkenes and gives no problem when alcohols are used as solvents[75,76]. 

CH3SCH3, CH3CN, (PhC0>202, 0°, 2 h, 75-95% yield. Acetonides, THP ethers, alkenes, ketones, and epoxides all survive these conditions. 

The introduction of a THP ether onto a chiral molecule results in the formation of diastereomers because of the additional stereogenic center present in the tetrahy-dropyran ring (which can make the interpretation of NMR spectra somewhat troublesome at times). Even so, this is one of the most widely used protective groups employed in chemical synthesis because of its low cost, the ease of its installation, its general stability to most nonacidic reagents, and the ease with which it can be removed. 

The THP ether can be converted directly to an acetate by refluxing in AcOH/AcCl (91 % yield). These conditions would probably convert other related acetals to acetates as well. The THP group can also be converted through the 0-SnBu3 to benzyl, MEM, benzoate, and tosylate groups. ... 

Ph2CHC02-2-tetrahydrofuranyl, 1% TsOH, CCI4, 20°, 30 min, 90-99% yield. The authors report that formation of the THF ether by reaction with 2-chlorotetrahydrofuran avoids a laborious proce ure that is required when dihydrofuran is used. In addition, the use of dihydrofuran to protect the 2 -OH of a nucleotide gives low yields (24-42%)." The tetrahydrofuranyl ester is reported to be a readily available, stable solid. A tetrahydrofuranyl ether can be cleaved in the presence of a THP ether. ... 

N HCl, THE, 0°, 100% yield. The ethoxyethyl ether is more readily cleaved by acidic hydrolysis than the THP ether, but it is more stable than the 1-methyl-1-methoxyethyl ether. 

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. 

ACOH/H2O, (3 1), 35°, 10 min, 100% yield. An IPDMS ether is more easily cleaved than a THP ether. It is not stable to Grignard or Wittig reactions, or to Jones oxidation. 

TiCl4, Et20, Lil, it, 61-91% yield. A THP ether was stable to these conditions, but methyl ethers can be cleaved. 

The (dextrorotatory) 11,15-bis-THP ether of PGp2a was also transformed into prostaglandins of the first series by selective hydrogenation of the Z-A bond (Ref. 3). 

Tonsil, a Mexican Bentonite, acetone, 30 min, it, 60-95% yield. MOM and MEM groups are stable and phenolic THP ethers were also cleaved." ... 

CAN, MeOH, 0°, 0.5-3 h, 81-95% yield. TBDMS ethers are more easily cleaved thus, a TBDMS ether is cleaved selectively in the presence of a THP ether (15 min, 95%). ... 

THP ethers can be converted directly to TBDMS and TES ethers using the silyl hydride and Sn(OTf)2 or the silyl triflate (70-95% yield). The use of TMSOTf gives the free alcohols upon isolation. ... 

From a THP ether TBDMSOTf, Me2S, CH2CI2, -50°, 24-97% yield. Allylic THP ethers are converted inefficiently. ... 

Ceric ammonium nitrate, MeOH, 0°, 15 min, 82-95% yield. Dioxolanes and some THP ethers are not affected, but in general, with extended reaction times, THP ethers are cleaved. 

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

In 1975, van der Baan and Bickelhaupt reported the synthesis of imide 37 from pyridone 34 as an approach to the hetisine alkaloids, using an intramolecular alkylation as the key step (Scheme 1.3) [23]. Beginning with pyridone 34, alkylation with sodium hydride/allyl bromide followed by a thermal [3,3] Claisen rearrangement gave alkene 35. Next, formation of the bromohydrin with A -bi omosuccinimide and subsequent protection of the resulting alcohol as the tetrahydropyranyl (THP) ether produced bromide 36, which was then cyclized in an intramolecular fashion to give tricylic 37. 

Silica gel successfully catalyzed the stereoselective synthesis of several glucoside terpenoids. Treatment of 49a with propan-2-ol, geraniol, the tetrahydropyranyl (THP) ether of coniferyl alcohol, and (—)-perillyl alcohol gave glucosides 52a-d in good yields (Scheme 12). The acid-labile THP group was retained under these reaction... 

Using day supported ammonium nitrate (dayan), selective deprotection of methoxyphenyl methyl (MPM) ether has been achieved recently using microwave irradiation in solvent-free conditions (Scheme 6.15) [56]. The same reagent has been used for the cleavage of tetrahydropyranyl (THP) ethers. A similar selective preparation and deavage of THP ethers has been achieved under microwave irradiation catalyzed by iodine [57] or neat reaction in an ionic liquid [28],... 

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