3,4-Dihydropyran

3,4-Dihydropyran (DHP) is a heterocyclic compound with the formula C5H8O. The six-membered C5O ring has the unsaturation adjacent to oxygen. The isomeric 3,6-dihydropyran has a methylene separating the double bond and oxygen. DHP is used for protecting group for alcohols. It is a colorless liquid.[1]

Dihydropyran
3,4-dihydropyran skelet
Names
Preferred IUPAC name
3,4-Dihydro-2H-pyran
Other names
2,3-Dihydro-4H-pyran, DHP
Identifiers
3D model (JSmol)
ChEMBL
ChemSpider
ECHA InfoCard 100.003.465
EC Number
  • 203-810-4
UNII
UN number 2376
  • InChI=1/C5H8O/c1-2-4-6-5-3-1/h2,4H,1,3,5H2
    Key: BUDQDWGNQVEFAC-UHFFFAOYAJ
  • 3,4 isomer: O1\C=C/CCC1
Properties
C5H8O
Molar mass 84.118 g·mol−1
Appearance Colorless liquid
Density 0.922 g/mL
Melting point −70 °C (−94 °F; 203 K)
Boiling point 86 °C (187 °F; 359 K)
Hazards
GHS labelling:
GHS02: FlammableGHS07: Exclamation mark
Danger
H225, H315, H317, H319
P210, P233, P240, P241, P242, P243, P261, P264, P272, P280, P302+P352, P303+P361+P353, P305+P351+P338, P321, P332+P313, P333+P313, P337+P313, P362, P363, P370+P378, P403+P235, P501
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa).
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Infobox references

Preparation

Dihydropyran is prepared by the dehydration of tetrahydrofurfuryl alcohol over alumina at 300–400 °C.[2] THFA is itself prepared from tetrahydro-2-furoic acid.

Reactions

In organic synthesis, the 2-tetrahydropyranyl (THP) group is used as a protecting group for alcohols.[3][4] Reaction of the alcohol with DHP forms a THP ether, protecting the alcohol from a variety of reactions. The alcohol can later be restored by acidic hydrolysis, concomitant with formation of 5-hydroxypentanal.[5]

Protection of an alcohol as THP ether followed by its deprotection. Both steps require acid catalysts.

See also

References
  1. Paul Ch. Kierkus (2001). "3,4‐Dihydro‐2H‐pyran". eEROS. doi:10.1002/047084289X.rd230.
  2. R. L. Sawyer and D. W. Andrus (1955). "2,3-Dihydropyran". Organic Syntheses.; Collective Volume, vol. 3, p. 276
  3. R. A. Earl L. B. Townsend (1990). "Methyl 4-Hydroxy-2-butynoate". Organic Syntheses.; Collective Volume, vol. 7, p. 334
  4. Arthur F. Kluge (1990). "Diethyl [(2-Tetrahydropyranyloxy)methyl]phosphonate". Organic Syntheses.; Collective Volume, vol. 7, p. 160
  5. Wuts, Peter G. M.; Greene, Theodora W. (2006). "Protection for the Hydroxyl Group, Including 1,2‐ and 1,3‐Diols". Greene's Protective Groups in Organic Synthesis (4th ed.). pp. 16–366. doi:10.1002/9780470053485.ch2. ISBN 9780470053485.
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