4-Methoxy-5,6-dihydro-2/7-pyrane

Vinyl ethers and a,P unsaturated carbonyl compounds cyclize in a hetero-Diels-Alder reaction when heated together in an autoclave with small amounts of hydroquinone added to inhibit polymerisation. Acrolein gives 3,4-dihydro-2-methoxy-2JT-pyran (234,235), which can easily be hydrolysed to glutaraldehyde (236) or hydrogenated to 1,5-pentanediol (237). With 2-meth5lene-l,3-dicarbonyl compounds the reaction is nearly quantitative (238). 

The reactions of 5,6-dihydro-2-methoxy-2H-pyran (101) with 1,3-dibromo-5,5-dimethylhydantoin in ether-methanol,137 and with ethanesulfenyl chloride,138 have been described by Baldwin and Brown. The former reaction gave a 2 1 mixture of the isomers 3/3-bromotetrahydro-2a ,4a-dimethoxypyran (102) and 3a-bromotetrahy-dro-2a,4/3-dimethoxypyran (103), respectively the structures and favored conformations of the isomers are shown. The reaction of ethanesulfenyl chloride with 5,6-dihydro-2-methoxy-2H-pyran (101)... 

Hydroboration was also employed"0 in the synthesis of methyl 2,3-dideoxy-4-0-methyl-a-DL-g/ /C(TO-pentopyranoside (182) from 3,4-di-hydro-2-methoxy-2H-pyran (181). Catalytic dealcoholation of 182 afforded 3,4-dihydro-3-methoxy-2f/-pyran (183), which, on bromination in methanol, gave"0 methyl 2-broino-2,3-dideoxy-4-0-methyl-a-DL-en/t/iro-pentopyranoside (184) as the main product. 

Addition of acetic acid to 6-(acetoxymethyl)-5,6-dihydro-2-methoxy-2ff-pyran (223) gave117118 three stereoisomeric 2,4-diacetoxy-6-(ace-... 

The greater hydrolytic lability of O-formyl than of O-benzoyl groups has been used in the preparation of ribonucleoside 2 -acetal 5 -esters.153 Acid-catalyzed reaction between 5,6-dihydro-4-methoxy-2//-pyran and N2-benzoyl-5 -0-benzoyl-3 -0-formylguanosine, followed by selective deformylation of the product with dilute methano-lic ammonia, gave N2-benzoyl-5 -0-benzoyl-2 -0-(4-methoxytetrahy-dropyran-4-yl)guanosine. 

The elimination of methanol, ethanol, or acetic acid is useful for the preparation of 4f/-pyrans, provided that the products exhibit sufficient stability. Thus the thermolyses of 2-ethoxy- and 2-acetoxy-2, 3-dihydro-4//-pyrans 265 undoubtedly led to unsubstituted 4//-pyran (5),18,293 but only when R = Ac was it possible to separate the unstable product 5 from reaction mixtures by GLC in 15 to 30% yields.18 Analogously, 25% of air-sensitive 2-methoxy-2//-pyran (267) was obtained on heating 266 with aluminum tri-butoxide under a nitrogen atmosphere at 155°C.33 A general technique for the preparation of condensed 4//-pyrans from their 2-ethoxy-2,3-dihydro derivatives is based on the elimination of ethanol in the presence of p-toluenesulfonic acid or polyphosphoric acid at decreased pressures293 to give... 

Hydroboration and oxidation of 3,4-dihydro-2-methoxy-2//-pyran gives a mixture of cis- and rra s-5-hydroxy-2-methoxytetrahydropyran (70CJC2334). After methylation, trans-2,5-dimethoxytetrahydropyran was isolated in small amounts. The cis isomer was obtained from 3,4-dihydro-3-methoxy-2//-pyran via 3-bromo-2,5-dimethoxytetrahydropyran. 

The reaction of 6-ethylthio-3,4-dihydro-2-methoxy-27f-pyran with aldehydes is promoted by SnCU, and has been used in the diastereoselective synthesis of highly functionalized tetrahydropyrans (Eq. 53) [88a] whereas the reaction of 2,2-diethoxy-6-(ethylthio)-3,4-dihydro-2//-pyran with aldehydes in the presence of SnCU gives aldol adducts of glutarates (Eq. 54) [88b]. 

C6H9N06 isosorbide 5-nitrate 16051-77-7 25.00 1 3721 2 7849 C6H10O2 3,4-dihydro-2-methoxy-2H-pyran 4454-05-1 -18.15 1.2099 2... 

Protection of chiral alcohols as THP ethers leads to mixtures of diastereoisomers. To avoid this problem, use 5,6-dihydro-4-methoxy-2JT-pyran. ... 

Beilstein Handbook Reference) BRN 0107274 2,3-Dihydro-2-methoxy(4H)pyran 3,4-Di-hydro-2-methoxy-2H-pyran EINECS 224-698-3 MDP 2-Methoxy-3,4-dihydro-2H-pyran NSC 44974 2H-Pyran, 3,4-dihydro-2-methoxy-. 

METHYSTICIN[Afe r k/K/ fariE 6056 12 62i8] H3-METHYSTICm 6-[2-(i,3-benzodioxoL5-yl)cthenyl]-5,6-dihydro-4-methoxy-2i/ pyran-2-one kavahin kavatin kavakin kawakin kanakin... 

The substrate for the synthesis of hexoses, rrans-5,6-dihydro-6-hydroxy-methyl-2-methoxy-2H-pyran (326,R = H), was resolved by means of its to-camphanyl ester into enantiomers. The Zcvo-rotating enantiomer was determined to have the 25 65 configuration. 

The steric effects involved in the cis-hydroxylation of 5,6-dihydro-2H-pyrans substituted at positions 6 and/or 2 with aqueous potassium permanganate were studied by Mochalin and co-workers. It was found that the reaction course is dependent on the steric hindrance exerted by the bulky substituent at C-2 both OH groups enter preferentially trans with respect to that substituent. In consequence, products of (x-lyxo or -erythro configuration are obtained in the case of di- or mono-substituted substrates. However, in the case of 5,6-dihydro-2-methoxy-2H-pyran, both possible stereoisomeric products, methyl 4-deoxy-a-and p-DL-eo t o-pentopyranosides, were formed in approximately equal amounts. 

Cjs-hydroxylation of 3,6-dihydro-2-methoxy-2H-pyran (341) afforded " a mixture of methyl 2-deoxy-a- and (3-DL-etyfAro-pentopyranosides (342). Hydrolysis of this mixture gave free 2-deoxy-DL-eo op ntos (2-deoxyribose). Compound 341 was obtained by the reductive removal of the p-toluenesul-fonyloxy group in methyl 3,4-dideoxy-2-0-p-toluenesulfonyl-a,p-DL-pent-3-eno-pyranoside (345). Mochalin °° obtained 341 in three steps starting from the Diels-Adler adduct 343 via the amide 344 and its Hoffman degradation in methanol solution. 

Sharpless oxyamination reagent, composed of chloramine-T and a catalytic quantity of osmium tetraoxide, was reacted with a series of 6-substituted 5,6-dihydro-2-methoxy-2H-pyrans. Both regioisomeric methyl 2,4-dideoxy-2-p-to-luenesulfonylamido- and 3,4-dideoxy-3-p-toluenesulfonylamido DL-/yjro-hexo-pyranosides (346 and 347) were obtained in yields of 40-60%, with the latter distinctly prevailing in mixtures. 

Me glycoside Methyl 3-deoxy-j3-D-g yceio-pentopyranosid-4-ulose. Dihydro-5-hydroxy-6-methoxy-2H-pyran-3 (4H ) -one... 

Dihydro-5-hydroxy-2-(hydroxymethyl)-477-pyran-4-one, D-675 Dihydro-5-hydroxy-6-methoxy-2 -pyran-3(477)-one, D-342 Dihydro-4-hydroxy-5-methyl-2(377)-furanone, D-707... 

Arentzen, R., YanKui,Y.T. and Reese, C.B. (1975) Improved procedures for the preparation of tetrahydro-4H-pyran-4-oneand 5,6-dihydro-4-methoxy-2H-pyran. Synthesis, 509-510. 

For the purposes of workup, it will appear as if two compounds are present with different Rf values, melting points, etc. This has been overcome by replacing 2,3-dihydropyran with 5,6-dihydro-4-methoxy-2H-pyran. The THP ether product is symmetrical. 

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