Pyrans, tetrahydro- from

Furfural — see Furan-2-oarbaldehyde, 532 Furfuryl acetate, o -(butoxycarbonyl)-anodic oxidation, 1, 424 Furfuryi acrylate polymerization, 1, 279 Furfuryl alcohol configuration, 4, 544 2-Furfuryl alcohol polyoondensation, 1, 278 reactions, 4, 70-71 Furfuryl alcohol, dihydro-pyran-4-one synthesis from, 3, 815 Furfuryl alcohol, tetrahydro-polymers, 1, 276 rearrangement, 3, 773 Furfuryl chloride reactions... 

Pyran, 3-chloro-3,4-dihydro-2,2-dimethoxy-synthesis, 3, 796-797 Pyran, 2-(chloromethyl)tetrahydro-5,10-pentadecadienol synthesis from, 1, 428 Pyran, 2-chlorotetrahydro-conformation, 3, 629 H NMR, 3, 579 Pyran, 4-chlorotetrahydro-synthesis, 3, 777... 

In the cyclization of the corresponding cis-epoxides, with the aim of obtaining the corresponding cis-2,3-disubstituted tetrahydropyrans, a similar trend was observed. For these systems, however, the 6-endo pathway was less favored, which was ascribed to difficulties in attaining a TS conformation that would allow for maximum stabilization of the developing p-orbital with the adjacent 7t-system. Alternatively, palladium-catalyzed cyclization of the tetrabutylammonium alkoxide derived from 33b results in the corresponding ris-2,3-disubstituted tetrahydro-pyran in excellent yield and selectivity (90%, dr >99 1), while the ris-epoxide gives stereoisomer 37b (86%, dr 98 2) [112]. 

Double deprotonation of tetrahydro-2-(2-nilroethoxy)-2//-pyran (8) and reaction with electrophiles provides a variety of substituted and functionalized nitroaldols1 Reaction with aldehydes affords 2-nitro-l,3-alkanediols 9 in 44 90% yield and high diastereoselectivities. From analogy of their II-NMR spectra and comparison with known compounds, the (R, R ) relative configuration is likely15. 

Addition of the dianion derived from tetrahydro-2-(2-nitroethoxy)-2//-pyran (8) to (5)-2-methylbutanal provides two of the four possible diastereomeric products in 64% yield. The major component, probably the (2/ ,3/ ,4.5)-diastereomer, is formed in 73% diastereoselectivity1S. 

The addition of (Z)-3-(alkylamino)-2-butenoic acid esters to nitroalkenes derived from open-chain sugars gave a 50 50 mixture of diastereomeric products 32. The reaction of chiral 2-sub-stituted l-(2-nitroethenyl)pyrrolidines with zinc enolates of 3-substituted tetrahydro-2//-pyran-2-oncs in 1,2-dimethoxyethane at — 78 °C afforded the corresponding 3,3-disubstituted products in 82-96% ee via an addition-elimination process33. The stereochemical course of the reaction was determined by chemical correlation of (S)-( )-3-ethyltetrahydro-3-(2-ni-troethenyl)-2//-pyran-2-one with ( + )-quebrachamine. 

Although alcohols are oxidized by tetra-n-butylammonium persulphate when the reaction is conducted in dichloromethane, tetrahydropyranyl ethers have been produced (>90%) when attempts to oxidize the alcohol are conducted in tetrahydro-pyran (see Chapter 10) [ 19], Tetrahydrofuranyl ethers have been prepared by an analogous method [20,21 ]. Base-mediated elimination of halo acids from P-halo alcohols under phase-transfer catalysed conditions produce oxiranes in high yield (70-85%). The reaction has particular use in the synthesis of epihalohydrins from p,y-dihalo alcohols [22],... 

In recent studies, Jamison and coworkers reported the formation of tetrahydro-pyran via cascade epoxide-opening reactions in water (Scheme 9) [96]. In this study, polytetrahydropyran precursor, such as 53, was synthesized from the epoxidation of polyalkene 52. 

Extracts of the male oil palm bunch moths, Tirathaba mundella Walker (Lepidoptera Pyralidae), were shown to contain four compounds namely, 5S, 65)-2,2,6-trimethyl-6-vinyl-tetrahydro-pyran-3-ol, 4-hydroxy-3-methoxy benzaldehyde (vanillin), 6,10,l4-trimethyl-2-pentadecanone, and the corresponding alcohol 6,10,l4-trimethyl-2-pentadecanol, which elicited responses from the females. However, when synthetic compounds were used in lures, the ketone and alcohol by themselves did not attract females, suggesting that they might not be an essential part of the blend. This can only be confirmed once their absolute configuration has been determined and the proper stereoisomers tested in the... 

Lovastatin and mevastatin Lovastatin, (lS,3R,7S,8S,8aR)-l,2,3,7,8,8a-hexahydro-3, 7-dimethyl-8-[-[2R,4R]-[tetrahydro-4-hydroxy-6-oxo-2H-pyran-2-yl]ethyl]-l-naphthyl (S)-2-methylbutyrate (20.2.7) is isolated from Monascus rubber [17] mA Aspergillus terreus [18], as is mevastatin (lS,3R,7S,8S,8aR)-l,2,3,7,8, 8a-hexahydro-7-metliyl-8-[-(2R,4R)-[tetrahydro-4-hydroxy-6-oxo-2H-pyran-2-yl]ethyl]-l-naphthyl (S)-2-metliylbutyrate (20.2.8), which is isolated from Penicillium citrinum [19, 20] as well as from Penicillium brevicom-pactum [21]. 

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... 

Diels-Alder reactions have featured heavily during the period of review. Ar-Vinyl-2-oxazolidinone has been reported as a dienophile for the first time, including the preparation of various tetrahydro-277,77/-pyrano[4,3-. ]pyrans <2002SL952>. The heterodiene cycloaddition reaction of 3-formylchromone with a series of ketene acetals formed from C2-symmetric l,2-diarylethane-l,2-diols is completely diastereoselective (Scheme 40) <1995J(P1)2293>. 

Removal of the auxiliary group from 12 (see p413) to give 13 followed by several steps yields (-)-(65)-tetrahydro-6-undecyl-2//-pyran-2-one (14), a pheromone of the wasp Vespa orientalis. Comparison of the optical rotation of the synthetic product with that of the natural product served to confirm the stereochemistry of the initial reduction to 12. 

Either enantiomer of a-alkylated alkanoic acids, 3-substituted dihydro-2(3//)-furanones and 3-substituted tetrahydro-2//-pyran-2-ones with known absolute configuration and high optical purities can be obtained from metalation and alkylation of chiral 4,5-dihydrooxazoles (see Section 1.1.1.4.3.). 

N,N, N"-tris (8-tetrahydro-2H-pyran-2yl)oxy-3-tosyl-6-oxa-3-azaoctyl)amine, 3. A 30.9-g sample of compound 1 is dissolved in 400 mL dry DMF and 6.1 g NaH (60% dispersion in mineral oil) is added. This reaction mixture is stirred at room temperature for 1.5 h, 10 g of anhydrous K2C03 is added, and the solution is heated to 100°C. A solution of 33.5 g of compound 2 in 100 mL DMF is then added dropwise over 1 h. Heating is continued for another 18 h. The insoluble material is filtered off, and the solvent is removed from the filtrate by evaporation under reduced pressure. The oily residue is dissolved in 300 mL ether, washed twice with 100 mL water, and dried over anhydrous Na2S04. Separation from Na2S04 hydrate and removal of ether leaves a yellow oil (57 g) of compound 3, which is used directly for the next step. 

Tetrahydro-2-vinylbenzaldehyde (13) has been synthesized from 2-s-butoxy-methylenecyclohexanone (70HCA485). Above 70 °C the aldehyde equilibrates with its valence isomer, the fused 2//-pyran (14). However, the ring-opened form is the thermodynamically favoured isomer. The pyran itself is unstable but has been trapped as the adduct (15) with TCNE (Scheme 1). 

Dihydro-2//-pyran (1.11 g, 13.2mmol) was added dropwise to a stirred solution of benzenesulfinic acid (1.88 g, 13.2 mmol) in dry dichloromethane at room temperature under argon. Stirring was continued for 2h, then the solvent was removed under reduced pressure and the product recrystallized from diethyl ether/petroleum to give 2-(benzenesulfonyl)tetrahydro-2//-pyran (1) (2.45 g, 82%) as white needles, m.p. 78°C. 

A novel acid-catalysed rearrangement of 2-hydroxy-2-phenylazo-y-butyrolactone (45) to the interesting /V-substituted tetrahydro-l,3-oxazine-2,4-dione derivative (46) has been reported.58 The photo- and thermo-chemistry of diazo(2-furyl)methane and diazo(3-furyl)methane have been investigated59 using matrix isolation techniques, and 3,7-diphenylpyrano[4,3-c]pyran-l,5-diones have been prepared60 from 5,5 -diphenyl-... 

Pravastatin was isolated as products of enzymatic hydroxylation by some kinds of microorganisms of [lS-[l-a(R ),7p,8P(2S, 4S )8a 3]]-2-methylbutanoic acid l,2,3,7,8,8a-hexahydro-7-methyl-8-[2-(tetrahydro-4-hydroxy-6-oxo-2))-pyran-2-yl)ethyl]-l-naphthalenic lactone (campactin) or their carboxylic acid or their salts (products of animal metabolism of microorganisms from the genera Nocardia, Streptomyces et cetera). 

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