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Widely used hydroxyl-protecting reagent3,4-Dihydro-2H-pyran is used as a hydroxyl-protecting reagent in organic synthesis. It acts as an intermediate in synthetic chemistry. It is used to protect various reactive functional groups. It is involved in the polymerization reaction either alone or with unsaturated compound and finds application in polymer industries. Further, it is employed in the preparation of bicyclic compounds of epoxide-fused, halo compounds and allenic alcohols.
Protects OH groups as their tetrahydropyranyl, (THP) ethers, stable to bases, Grignard or organolithium reagents, metal hydrides, etc., but readily removed by mild acid. Introduction (acetal formation) generally employs an acid catalyst, often p-TsOH. For example of protection, reaction with Grignard, and deprotection, see: Org. Synth. Coll., 7, 334 (1990). For alternative catalysts for THP ether formations, see: Pyridinium p-toluenesulfonate, A15708, Triphenylphosphine hydrobromide, L14290, Boron trifluoride diethyl etherate, A15275, Amberlyst® 15, 89079, Montmorillonite K10, L15160, Acetonyltriphenylphosphonium bromide, B22434, Indium(III) trifluoromethanesulfonate, 40131. Sulfuric acid/ silica gel: Synth. Commun., 22, 159 (1992), allows the catalyst to be removed by simple filtration. POCl3, described for the protection of diethyl hydroxymethylphosphonate, permits use in the Horner-Wadsworth-Emmons reaction: Org. Synth. Coll., 7, 160 (1990). See also Iodotrimethylsilane, A12902, providing non-acidic conditions; cf also Tetrahydropyran, A13392. For selective monotetrahydropyranylation of symmetrical diols, catalyzed by acidic ion-exchange resin, Dowex® 50WX2 50-100 (H), L13943, see: J. Org. Chem., 63, 8183 (1998).
For selective deprotection of THP ethers under non-acidic conditions with LiCl in wet DMSO, see: J. Org. Chem., 61, 6038 (1996).
The lithio-derivative, formed with tert-BuLi, reacts with, e.g. alkyl iodides or carbonyl compounds: Tetrahedron Lett., 4187 (1977).
Acetals and ortho esters, in the presence of Lewis acid catalysts, add readily to the vinyl ether system: Chem. Lett., 1101 (1988).
Can, K. H.; Şahin, Ö. Design, Synthesis and Characterization of 3,4-Dihydro-2H-pyran Containing Copolymer/Clay Nanocomposites. J. Macromol. Sci. Part A Pure Appl. Chem. 2015, 52 (6), 465-475.
Donslund, B. S.; Monleón, A.; Larsen, J.; Ibsen, L.; Jørgensen, K. A. The stereoselective formation of highly substituted CF3-dihydropyrans as versatile building blocks. Chem. Commun. 2015, 51 (71), 13666-13669.
Hazard Statements: H225-H315-H317-H319
Highly flammable liquid and vapour. Causes skin irritation. May cause an allergic skin reaction. Causes serious eye irritation.
Precautionary Statements: P210-P233-P240-P241-P242-P243-P261-P264b-P272-P280-P303+P361+P353-P305+P351+P338-P333+P313-P337+P313-P363-P370+P378q-P501c
Keep away from heat/sparks/open flames/hot surfaces. - No smoking. Keep container tightly closed. Ground/bond container and receiving equipment. Use explosion-proof electrical/ventilating/lighting/ equipment. Use only non-sparking tools. Take precautionary measures against static discharge. Avoid breathing dust/fume/gas/mist/vapours/spray. Wash face, hands and any exposed skin thoroughly after handling Contaminated work clothing should not be allowed out of the workplace. Wear protective gloves/protective clothing/eye protection/face protection. IF ON SKIN (or hair): Remove/Take off immediately all contaminated clothing. Rinse skin with water/shower. IF IN EYES: Rinse cautiously with water for several minutes. Remove contact lenses, if present and easy to do. Continue rinsing. If skin irritation or rash occurs: Get medical advice/attention. If eye irritation persists: Wash contaminated clothing before reuse. In case of fire: Use CO2, dry chemical, or foam Dispose of contents/ container to an approved waste disposal plant