Spectra tetrahydropyran

In 2007, another departure from carbonyl-type activation was marked by Kotke and Schreiner in the organocatalytic tetrahydropyran and 2-methoxypropene protection of alcohols, phenols, and other ROH substrates [118, 145], These derivatives offered a further synthetically useful acid-free contribution to protective group chemistry [146]. The 9-catalyzed tetrahydropyranylation with 3,4-dihydro-2H-pyran (DHP) as reactant and solvent was described to be applicable to a broad spectrum of hydroxy functionalities and furnished the corresponding tetrahydro-pyranyl-substituted ethers, that is, mixed acetals, at mild conditions and with good to excellent yields. Primary and secondary alcohols can be THP-protected to afford 1-8 at room temperature and at loadings ranging from 0.001 to 1.0mol% thiourea... 

X-Ray analysis of hexahydrofuro[2,3- ]pyran derivative 39 shows that the tetrahydropyran ring assumes a chair conformation with the C(7a)-0(1) bond found in the axial position <1998T8753>. This conformation agrees with that obtained by analysis of the NMR spectrum of 39. 

Although the 13C spectrum of tetrahydropyran was reported in 1965 (65JPC3925), almost a decade passed before this saturated system was investigated by this technique. 

The vacuum UV spectrum of the dihydropyran (13) in solution shows a broad band (Amax 195 nm) (48JCPI 17)466), but that of the vapour of tetrahydropyran consists of two systems of closely spaced narrow bands, one beginning at 193 nm and the other, of higher intensity, at 184 nm (51JA4865). 

The photoelectron spectrum of tetrahydropyran has been recorded (72JA5599), and analyzed along with the spectra of 3,4-dihydro-2//-pyran and 4//-pyran (78HCA1388). 

A one-to-one solution of 3-CP in tetrahydropyran was prepared and irradia ed under identical conditions. The spectrum was essentially the same. 

A complete assignment of the H NMR data for tetrahydropyran (THP) 140 has been reported <1998J(P2)1751>. At room temperature the 400 MHz spectrum of THP in 1 1 CDCl3 CFCl3 consists of three multiplets at S 3.63, 1.64, and 1.57 in a ratio of 2 1 2 (H(2), H(4), and H(3)). At -85 °C, all of the resonances are resolved and the assignment of axial and equatorial protons is possible. This data, in conjunction with the previously reported study of the coupling constants of tetrahydropyran and comparison with cyclohexane data (Table 11) <1976JOC1380>, provide a complete picture of the NMR of tetrahydropyran. 

Finally, our studies show all divinyl ether-maleic anhydride copolymers examined to date to be a mixture of the 5-membered and 6-membered bicyclic structures. The primary evidence for this, of course, is the presence of peak B at ca. 35 ppm which is assigned to the methylene carbon on a tetrahydropyran ring. Major features of the spectrum can be readily explained based on the available data present by both us and Professor Kunitake. However, still in question is the meaning of the fine structure contained particularly in peaks D, E, and F with respect to the relative stereochemistry of the copolymer as produced. 

Kunitake and Tsukino ( 0 also used 13c NMR to determine ring size in the copolymer, but they calculated chemical shifts by extrapolating published data on simpler cyclic compounds. By this method they concluded that a copolymer prepared in chloroform contained only tetrahydrofuran rings. However, their published spectrum of the copolymer contained the same peak B as ours, and therefore the copolymer must consist of both five- and six-membered rings. The spectrum of a copolymer prepared in acetone-carbon disulfide was too poorly resolved to show peak B, but Kunitake and Tsukino estimated the polymer to contain about 90% tetrahydropyran rings. 

Hoffmaniolide (180) has been isolated from Prorocentrum hoffmannianum The gross structure of hoffmaniolide (180) was obtained by analyzing the liquid secondary ion mass spectrometry (LSIMS)-MS/MS spectrum as well as 2D NMR such as H- H COSY, TOCSY, and HMBC, and the relative stereochemistry of a tetrahydropyran ring was obtained from J coupling data. Isolation of hoffmanniolide (180) from P. hoffmannianum suggested a biosynthetic capability of this genus to produce either linear or macrocyclic polyethers. 

Fig. 8J. 25 MHz, 3C-NMR spectrum of racemic poly(tetrahydropyran-2,6-diyloxymethylene) prepared in CH2C12 at —78 °C. 7% wt soln in CDClj 421...

Despite the characteristic features in the spectra of furanoses, some caution (24) should be exercised to exclude the possibility of rearrangements when interpreting the mass spectrum of an unknown. It has been reported (25) that isomeric tetrahydrofuran and tetrahydropyran diacetates have virtually identical mass spectra due to rearrangement of the latter to give after appropriate eliminations, a common cyclic oxonium ion at m/e 71. 

To assist in the interpretation of carbohydrate infrared spectra, one approach is to make use of model compounds which are of a simple nature but have similarities with the structure of the carbohydrate being examined. For example, tetrahydropyran is such a model compound since it contains the pyranose ring which is found in sugars. A knowledge of its spectrum can assist in the study of, and interpretation of, carbohydrate spectra. 

To demonstrate the utility of the tandem CM/thermal Sn2 reaction, we embarked on a synthesis of ( )-diospongin A (335). The diarylheptanoids diospongin A and B (335 and 336, Fig. 3.3) were isolated from the rhizomes of Dioscorea spongiosa [32] by Kadota and coworkers in 2004 and have attracted considerable synthetic interest due to antiosteoporotic activity (diospongin B) [33-41]. Their structures, including absolute stereochemistry, were determined by NMR data, Mosher ester analysis and the CD spectrum [42]. We envisioned that the 4-hydroxy-2,6-cfr-tetrahydropyran embedded in 3.55 could be accessed by using the tandem CM/thermal 8 2 reaction as the key bond-forming event. 

---