Pyrans, dihydro tetrahydro

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... 

Beckmann rearrangement, 3, 710 Pyran-4-carbaldehyde, 2,2-dimethyl-tetrahydro-Reformatsky reaction, 3, 732 4H-Pyran-4-carbaldehydes synthesis, 3, 760-761 Pyran-2-carbonitrile, 5,6-dihydro-reactions, 3, 732... 

The addition of the lithium enolates of various acetic add esters to (S)-3-(4-methylphcnyl-sulfmyl)-2(5//)-liiranone and (,S)-5,6-dihydro-3-(4-methylphenylsulfinyl)-2//-pyran-2-one gives, after desulfurization with Raney nickel, 4-substituted dihydro-2(3//)-furanoncs and 4-substituted tetrahydro-2//-pyran-2-ones, respectively, in good to quantitative enantiomeric excess. Addition of the enolate occurs via the nonchelate mode. The enolate of methyl (phenylthio)acetatc is best overall in regards to chemical yields and enantiomeric purity of the final lactone product13. 

Propionic acid, 2-iodo-3-nitro-, ethyl ester [Propanoic acid, 2-iodo-3-mtro-, ethyl ester], 65 2//-Pyran, 3,4-dihydro-, 51 2//-PYR AN-2-ONE, 49 2H Pyran 2-one, 5 bromo 5,6-dihydro, 50 27/-PYRAN-2-ONE, 5,6 DIHYDRO-, 49 PYRIDINE, 2,3,4,5 TETRAHYDRO, 118 Pyridines, -substituted, 34 a Pyrone-6-carboxyhc acid [2H Pyran-6-Larboxyhc acid 2-oxo ], 51 Pyrroles, 34... 

Pyran, 3,4-dihydro-, 55, 63 Pyran, tetrahydro-, 2,3-dichIoro- [2//-Pyran, tetrahydro-, 2,3-dichloro-], 55, 63 Pyran, tetrahydro-, 3-chloro-2-methyl- [2H-Pyran, tetrahydro-, 3-chloro-2-methyl-], 55 63... 

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... 

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.). 

Preparation of 3-Substituted Dihydro-2(3f/)-furanones and 3-Substitutcd Tetrahydro-2A/-pyran-2-ones... 

Disproportionation has been observed frequently with thiopyrans and rarely with 4//-pyrans, and all cases involve a tetragonal carbon center (position 2 or 4) bearing at least one C—H bond. Some molecules of the substrate are aromatized to corresponding thiopyrylium or pyrylium ions and others reduced to dihydro or tetrahydro products. The relative abilities of pyrans and thiopyrans to disproportionate were interpreted within a proposed hydride transfer mechanism by a CNDO/2 method.45... 

Stepwise catalytic reduction of pyran-2-ones to the dihydro (300) and tetrahydro (301) pyran-2-ones is achieved by suitable choice of catalyst and reaction conditions (Scheme 17). Anhydrous copper(II) sulfate simultaneously dehydrates the alcohol (78JHC1153). 

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. 

Chemical Name 2H-Pyran-2-acetic acid, 6-(2-(2-(5-(6-ethyl-3,6-dihydro-5-methyl-2H-pyran-2-yl)-3-methyl-l,4-hexadienyl)-3-methylcyclopropyl) ethenyl)tetrahydro-4,5-dihydroxy-... 

Pterins are redox active in their own right and can adopt one of several oxidation levels, for example, fully oxidized, dihydro, or tetrahydro (Fig. 18). The stereochemical nature of MPT observed in each protein crystallographic study (13) is equivalent to that of the fully reduced, or tetrahydropterin, state. This argues against the existence of dihydropterin states such as 5,6-dihydrop-terin or 7,8-dihydropterin, and one of the various quininoid forms of the dihydropterin, in the crystalline forms of these enzymes that have been characterized by X-ray crystallography. However, it is important to note that, for the tricyclic structure of MPT, the tetrahydropterin state is equivalent to that of a dihydropterin, as manifest in the pyran ring-opened form of the bicyclic... 

TLC analysis was carried out on precoated plastic silica gel plates (with fluorescent indicator) using diethyl ether as eluant. With this eluant, the R of starting material is 0.50 and the Ri of 3,4-dibromo-3,4,5,6-tetrahydro-2(H)-pyran-2-one is 0.83. In addition to these two spots, a third spot, R = 0.55, corresponding to 3-bromo-5,6-dihydro-2(H)-pyran-2-one was detected. TLC analysis is not always reliable and it is better to analyze a small aliquot by NMR. 

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