Vinyl Tetrahydropyrans

Further condensation of the free hydroxyl group of 177 with another molecule of 

The yields ranged from good to excellent, and the syn-2,6-disubstituted tetrahy-dropyran products 203 were formed stereoselectively. The facial selectivity in the addition to the aldehyde, however, was minimal, as might be expected considering the distance between the reactive end of the enol function and the stereogenic center in enols 200 and 201. 

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Let s now consider concerted skeletal rearrangements which allow the direct transformation of a sugar structure into a carbocyde. The Claisen rearrangement has been used for the direct conversion of sugar C-glycosides to eight membered carbocycles, respectively. The reaction has precedents in the transformation of 2-methylene-6-vinyl-tetrahydropyrans to cyclooctenone derivatives, a transformation that has been applied in the synthesis of several natural products [54],... 

For cyclic molecules, the substitution is fast if the leaving group is in pseudoxial position and slow if in pseudoequatorial position [56]. Therefore, when the C-O bond can occupy a perpendicular direction to the C=C double bond, the reaction occurs rapidly. The following example illustrates this observation, since the 5-H dihydropyran 123 does not react with a Grignard reagent in the presence of Cu catalyst, whereas the vinyl tetrahydropyran 124 (which can present a conformer in which the intracyclic C O bond is perpendicular to the C=C double bond) reacts rapidly [56 Eq. (40)]. 

In 2006, Widenhoefer reported an effective gold(I)-catalyzed protocol for the exo-hydroalkoxylation of y- and 6-hydroxy allenes to form 2-vinyl tetrahydrofurans and 2-vinyl tetrahydropyrans, respectively [104]. For example, treatment of 1-phenyl-5,6-heptadienol with a catalytic 1 1 mixture of [P(f-Bu)20-biphenyl]AuCl and AgOTs in toluene at room temperature led to isolation of 2-phenyl-6-vinyltetrahydropyran in 96% yield as a 7.2 1 mixture of diastereomers (Eq. (12.33)). This gold(I)-catalyzed hydroalkoxylation protocol tolerated substitution at the terminal allenyl carbon atoms and along the alkyl chain that tethered the hydroxy group to the allenyl moiety and was also effective for the S-exo hydroalkoxylation of y-hydroxy allenes. Alcaide and Almendros have shown that gold(III) also catalyzes the S-exo hydroalkoxylation of y-allenyl alcohols in modest yields (Eq. (12.34)) [105]. 

Schmidt et al. [74] prepared spirocyclic lactones by hydroformylation-acetalization of vinyl-tetrahydropyranes followed by Ley-Griffith oxidation (Scheme 5.82). Versatile building blocks were obtained after cleavage of the lactone ring, which were suitable for the synthesis of natural compounds such as pseudomonic acid A (C-glycoside). 

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) ... 

Dimethoxy-2- l- 2-(tetrahydropyran-2-yloxy)ethyl]vinyl -l,3,6-oxadiazepine (4) Single Procedure 320... 

The cyclization of the homologous epoxide 36 under acidic conditions was also investigated (Table 9.5) [110]. As would be expected, compound 36a reacted by a 6-exo cyclization to give tetrahydropyran 38a (Entry 1). The a, 3-unsaturated hydroxy epoxide 36b gave a 1 3.5 mixture of oxepane 37b and tetrahydropyran 38b (Entry 2). Subjection of 36c and 36d, which both contain more electron-rich 71-systems, to the reaction conditions resulted in preferential 7-endo cyclization to give 37c and 37d, thus confirming the powerful regiodirecting effect of the vinyl moiety (Entries 3 and 4). 

Aubele et al. studied the aqueous Prins cyclization using cyclic unsaturated acetals as oxocarbenium ion progenitors and allylsilanes are used as nucleophiles. Cyclizations proceed efficiently inside Lewis acidic micelles (of cerium salt) in water. A variety of vinyl- and aryl-substituted tetrahydropyrans with excellent stereocontrol was obtained (Eq. 3.26).113... 

As these acetals could be converted into the 4,6-O-ethylidene derivatives on treatment with acid, it was reasoned that use of a cyclic vinyl ether, namely, 3,4-dihydro-2H-pyran, might prevent this second process, thus leading to a more useful method of selective acetalation.338 An equimolar reaction with methyl a-D-glu-copyranoside for 4 days in N,N-dimethylformamide led to utilization of 88% of the glycoside, and the 6-(tetrahydropyran-2-yl) ether constituted —85% of the crude reaction-product. In contrast to the steric control apparent in this instance, reaction of 3,4-dihydro-2H-pyran with the axial and equatorial hydroxyl groups in dl-1,4,5,6-tetra-O-acetyl-mi/o-inositol was completely unselective,339 a fact that has been rationalized310 in terms of the probable mechanism of these reactions. 

Di- or tetrahydropyrans with vinyl side chains obtainable by diastereo-selective ring closing metathesis or by addition of vinylmagnesium chloride to appropriately functionalized tetrahydropyranones are converted to spirocyclic hemiacetals under hydroformylation conditions (Scheme 4) [33]. Oxidation yields the corresponding lactones. 

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

The polymerization kinetics of alkali salts of living vinyl polymers In ethereal solvents, such as tetrahydrofuran CD, tetrahydropyran (2), dlmethoxyethane Q), oxepane (4) and dloxane... 

Details of the Janda-Chen synthesis were as follows. A tetrahydropyran (THP) linker was attached to the NCPS support enabling attachment of alcohols via THP ether formation.13 The THP-NCPS resin 1 is derivatized with / -(+)-4-hydroxy-2-cyclopentanone 2, giving the THP ether-based resin 3, followed by coupling of the C13 20 fragment by enone-cuprate addition. The cuprate required was generated from the corresponding E-vinyl stannane 4. The resulting enolate was trapped as the silyl end ether... 

Unsaturated tetrahydropyran derivatives have received only cursory attention in the literature as heterocyclic monomers. 2,3-Dihydropyran and several of its substituted derivatives apparently undergo cationic polymerization in a manner typical of vinyl ethers (72MI11103), while tetrahydropyranyl esters of methacrylic acid (123) are fairly typical free radically polymerizable monomers (Scheme 35) (74MI11105). The THP group was used in this study as a protecting group for the acid functionality, and it was found that deprotection of polymers (124) could be accomplished under extremely mild conditions. 

The levels of 1,5-asymmetric induction in the palladium-catalyzed alkoxy-carbonylations of alkenols to form 2,6-disubstituted tetrahydropyrans have been shown to be quite reasonable (Table 10 and equation 50).144 Recent studies have shown that cyclization with palladium(II) acetate in DMSO in the absence of CO results in controlled -hydride elimination to form vinyl-substituted tetrahydropyrans with high levels of 1,4- and 1,5-asymmetric induction (equation 51).144b... 

Catalytic oxy-palladation is an extremely useful method for the synthesis of functionalized THF and tetrahydropyran moieties. This reaction is brought about simply by treating a 1,4- or 1,5-hydroxy alkene with 0.1 mol-eq of Pd(II) salts and copper(I) chloride in DMF, with oxygen (equation 181)655. If this reaction is carried out in the presence of carbon monoxide in methanol, then an ester moiety is introduced into the product molecule (equation 182)656-658. If an alkene is introduced in place of the CO, then a tandem vinylation reaction also takes place (equation 183)659. 

Cleavage-cationic cyclization of bromocyclopropanes. Bromocyclopropanes sub-st i tuted by a suitably situated hydroxyl or carboxyl group undergo cleavage-cyclization at 25° in the presence of 1-1.5 equiv. of AgOCOCF3 or Hg(OAc)2. Vinyl lactones, tetrahydropyranes, or tetrahydrofuranes can be prepared in this way.1... 

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... 

The synthesis of 5- -methylene tetrahydropyrans 378 can be accomplished by a regioselective ruthenium catalyzed C-C coupling reaction of prop-2-yn-l-ols 379 and allylic alcohol (Equation 156) <1999JOC3524>. A ruthenium catalyzed alkylative cycloetherification reaction between allene 380 and vinyl ketones furnishes 2-substituted tetrahydropyrans 381 in high yield (Equation 157) <1999JA10842>. 

Treatment of the vinyl acetals 384 with triisobutylaluminium results in the transposition of an O-atom with a C-atom on the ring, providing tetrahydropyrans 385 in excellent yield (Equation 160, Table 19) <1996TL141>. 

Glasses. The solvents used to form the glass with polymers should be clear in the UV region to allow maximum absorption of radiation by the polymer. The ESR of irradiated solvents should not interfere with that of the polymer. Three solvents were found to be close to ideal tetrahydrofuran (THF) p-dioxane (DX) and tetrahydropyran (TP). All three were purified by repeated distillation and column chromatography. Poly(vinyl chloride) and the copolymer solutions (5-15%, w/v) were prepared from these solvents, degassed, sealed under vacuum (10-6 torr), and irradiated. 

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. 

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