Tetrahydropyran rings

Retrosynthetic disassembly of the tetrahydropyran ring in 14, a mixed cyclic ketal, provides ketone 15 as a plausible precursor. In the synthetic direction, the solvolytic cleavage of the ester functions in 15 would likely be attended by the formation of a cyclic hemi-ketal. On treatment with acidic methanol, this substance could then be converted to mixed ketal 14. 

There are two possible ways for the ring opening of 35 in the polymerization The C1—O7 bond cleavage leads to the formation of a substituted tetrahydropyran ring 36 in the polymer chain, while the C1—O2 bond cleavage produces a substituted tetrahydrofuran ring 37. Product analysis of the acid-catalyzed hydrolysis of the... 

The cyclic dimer, tetramer, and hexamer can be crystallized in acetonitrile, and also in chloroform (the former two oligomers). X-ray analysis of the crystals of the cyclic dimer47 disclosed that it consisted of a pair of different enantiomers of 53 and that all of the four substituents attached to the two tetrahydropyran rings occupied the axial position as illustrated in Fig. 54s). Such a conformation is in... 

Proton noise decoupled 13C-NMR spectra of equimolar mixtures of the cyclic hexamer and metal thiocyanates showed that the signals of the carbonyl carbon and two methine carbons gave downfield shifts upon the addition of metal thiocyanates, while those of the three methylene carbons of the tetrahydropyran ring gave upfield... 

Cyclic hemiacetals or hemiketals of sugars with a five-membered (tetrahydrofuran) ring are called furanoses, those with a six-membered (tetrahydropyran) ring pyran-oses. For sugars with other ring sizes see 2-Carb-5. 

A disadvantage of the THP group is the fact that a new stereogenic center is produced at C(2) of the tetrahydropyran ring. This presents no difficulties if the alcohol is achiral, since a racemic mixture results. However, if the alcohol is chiral, the reaction gives a mixture of diastereomers, which may complicate purification and/or characterization. One way of avoiding this problem is to use methyl 2-propenyl ether in place of dihydropyran (abbreviated MOP, for methoxypropyl). No new chiral center... 

A tandem combination initiated by a Mukaiyama reaction generates an oxonium ion that cyclizes to give a tetrahydropyran rings.48... 

Fall D, Duval RA, Gleye C, Laurens A, Hocquemiller R. Chamuvarinin, an aceto-genin bearing a tetrahydropyran ring from the roots of Uvaria chamae. J Nat Prod 2004 67 1041-1043. 

Rychnovsky and coworkers very recently described a so-far unknown domino Michael addition/2 -oxonia Cope/aldol-type reaction to give tetrahydropyran rings [475]. The transformation has as its origin an annulation process (see Section 2.1) which was discovered by the same group. 

The structure of the antibiotic, 9, which has been variously named lacto-quinomycin-A and medermycin, was first reported by Okabe and coworkers in 1985.58 In early 2002,59 a communication was published reporting that the original structure, 9, was incorrect based on synthesis and that the substituted tetrahydropyran ring was attached to the 6-position to give 10, rather than the 8-position as originally reported. The authors based their conclusion on the fact that a key intermediate was identified as 6-bromo-3-hydroxybenzaldehyde rather than the 4-bromo-3-hydroxy benzaldehyde as previously reported.60... 

The oxidation of enol ethers at a reticulated vitreous carbon anode [2, 3] (Scheme 1) in a mixture of methanol/THF containing tetraethylammonium tosylate as the electrolyte and 2,6-lutidine as the base leads to substituted tetrahydrofu-ran and tetrahydropyran rings in good yields (51-96%). The major product obtained had a trans-stereochemistry. The cyclization failed to make seven-membered ring products. In order to determine the... 

Under reasonable conditions tetrahydropyran ring is not affected. Catalytic hydrogenation of 1,2-dihydropyran over Raney nickel at room temperature and 2.7 atm saturated the double bond to give quantitative yield of tetrahydropyran [634. ... 

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