F Tetrahydropyran

Tetrahydronaphthalene, 3300 f Tetrahydropyran, 1965 Tridecanal, 3619 f Vinyl acetate, 1532 f 4-Vinylcyclohexene, 3004... 

Sodium 5,8,11,14-eicosatetraenoate, 3803 Sodium ethoxyacetylide, 1474 1,1,2,3-Tetrachloro-1,3-butadiene, 1385 f Tetrahydrofuran, 1607 Tetrahydronaphthalene, 3294 f Tetrahydropyran, 1959 Tridecanal, 3613 f Vinyl acetate, 1527 f 4-Vinylcyclohexene, 2999 See Indane-2-aldehyde ACETYLENIC COMPOUNDS ALKALI METALS ALKENES ALKYNES... 

Thiazolo[4,5-d]pyrans [CjNS-CsO]. 2-Dimethylamino-thiazoles will undergo cycloaddition with two moles of t-butylcyanoketen to give a mixture of two thiazolo[4,5-f/]tetrahydropyran-2-ones (153 = H or Me, = CN, R =... 

Alkoxyall l All l Peroxides. / /f-Butyl tetrahydropyran-2-yl peroxide [28627 6-5] (1), where R = tert — butyl, X = OR", R = H, R and R" = 1, 4 butanediyl, has been isolated. This is one of many examples of alkoxyalkyl alkyl peroxides which may be prepared by reaction of hydroperoxides with vinyl ethers (139) ... 

We have studied the anodic oxidation of unsaturated alcohols using the controlled potential electrolysis (E = 1.9V vs SCE) in CH3CN-O.I mol/1 Et4NC104 solution in a divided cell [110]. The oxidation of 4-pentenol after consumption of 0.8 F/mol gave 2-methyltetrahydrofuran and tetrahydropyran as the major products. The oxidation of 5-pentenol gave 2-methyltetrahydro-pyran and oxepam, while the oxidation of 3-butenol under the same reaction conditions did not give the cyclic products. We rationalized this reaction as the electrongenerated acid (EGA) catalyzed intramolecular cyclization (Scheme 44). 

The decomposition of arenediazonium tetrafluoroborates in the resulting fluoroarene as solvent has also been utilized.179 This method is very fruitful in the synthesis of fluorobenzene (96% yield) or fluorotoluenes (85-88% yield for the three isomers) but fails with substrates such as anisolediazonium tetrafluoroborates which probably arylate the reactive fluoroaromatic solvent. In contrast, perfluorinated tertiary amines (EF-L 174, F-C 40), perfluorinated alkyl tetrahydropyran (EF-L 102), perfluorodecahydronaphthalene (Flutec PP7) or other per-fluorocycloalkanes (Flutec s) are claimed to be the best media for fluorodediazoniation of all types of diazonium tetrafluoroborates.224 These media seem to be more efficient, at least in the synthesis of 1,2-difluorobenzene, than silicone oil which has also been claimed to improve fluorodediazoniation.225... 

The unsubstituted pentanedial yields the parent 4/f-pyran on successive treatment with hydrogen chloride and A AT-diethylaniline (62AG465). This two-step approach involving elimination of hydrogen chloride from the initially formed tetrahydropyran has been extended to the synthesis of substituted 4/f-pyrans (Scheme 15) (67MI22400). 

Analogous photorearrangements have been reported for other cyclic peroxides,194 and the conversion of the peroxide (243) to the benzo-furo[3,2-h]naphtho[l,2-d]furan (244) is believed to involve an intermediate oxiran.195 Studies of the photodecomposition of 3,4-dihydro-2/f-pyrans,196 tetrahydropyran,197 and 1,4-dioxan198 have been reported. 

Tetrahydropyran (THP) has been found to be a poor substrate in the present a-C-H hydroxyalkylation reaction (20% yield dr 80 20). This result seems to be related to the previous observation of the low susceptibility to hydrogen abstraction of THP. See Refs, [le, f). 

Anodic oxidation of homo allyltrimethylsilylmethyl ethers 238 or homo allyl trimethyl-stannyl methyl ethers in the presence of tetrabutylammonium tetrafluoroborate results in the formation of fluorine- containing tetrahydropyrans 239249(equation 131). The process involves formation of a resonance stabilized carbocation and its intramolecular cycliza-tion by the participation of a neighboring vinyl group, followed by attack of fluoride ion. This process is a convenient way to form the C—F bond involving electrochemical steps. 

L. F. Wiggins, Advan. Carbohydrate Chem. 5, 191-228 (1950). Tetrahydropyran, sugar moiety in streptomycin ... 

Phenols add intramolecularly to Michael acceptors. " Under acidic conditions, a one-pot sequence starts with initial electrophilic acetylation of the activated aromatic ring and is followed by cyclization." With an appropriate leaving group in the /f-position (OMe. or other amines such as in the unsaturated carbonyl compound (e.g., 4) is formed. Other approaches to pyroncs include the self-condensation of protected //-hydroxy acrylates,intramolecular aldol reactions followed by condensation,thermal cycli-zations of unsaturated ()-chloro esters,and an iodo-cyclization-elimination sequence w th Michael acceptors.Oxymercuration of an unsaturated alcohol is an alternative cyclization approach to tetrahydropyrans. 

An anomeric effect is observed in 3,4-dihydro-2/f-pyrans. For example, a 2-alkoxy group preferentially occupies an axial position (71DOK(i96)367). Indeed, a study of the NMR spectra of some 2-alkoxy-3,4-dihydro-2//-pyrans and their 4-methyl derivatives established that the anomeric effect was more important in the unsaturated heterocycles than in the corresponding tetrahydropyrans (72BSF1077). The axial preference of an alkoxy group is even more accentuated when the double bond is associated with a fused benzenoid ring, as in the 2-alkoxychromans. It is also of interest to note that the role of the polarity of the solvent on the conformational equilibrium is less important than for the saturated analogues. 

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