3,4-Dihydropyran

Dihydropyran
Names
	Preferred IUPAC name 3,4-Dihydro-2H-pyran
	Other names 2,3-Dihydro-4H-pyran, DHP
Identifiers
CAS Number	110-87-2 ;
3D model (JSmol)	3,4 isomer: Interactive image;
ChEMBL	ChEMBL3184439;
ChemSpider	7789 ;
ECHA InfoCard	100.003.465
EC Number	203-810-4;
PubChem CID	8080;
UNII	T6V9N71IHX;
UN number	2376
CompTox Dashboard (EPA)	DTXSID6041426 ;
	InChI InChI=1/C5H8O/c1-2-4-6-5-3-1/h2,4H,1,3,5H2 Key: BUDQDWGNQVEFAC-UHFFFAOYAJ;
	SMILES 3,4 isomer: O1\C=C/CCC1;
Properties
Chemical formula	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:
Pictograms
Signal word	Danger
Hazard statements	H225, H315, H317, H319
Precautionary statements	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). verify (what is ?) Infobox references

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]

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.

References

^ Paul Ch. Kierkus (2001). "3,4-Dihydro-2H-pyran". EEROS. doi:10.1002/047084289X.rd230. ISBN 0471936235.
^ R. L. Sawyer and D. W. Andrus (1955). "2,3-Dihydropyran". Organic Syntheses; Collected Volumes, vol. 3, p. 276.
^ R. A. Earl L. B. Townsend (1990). "Methyl 4-Hydroxy-2-butynoate". Organic Syntheses; Collected Volumes, vol. 7, p. 334.
^ Arthur F. Kluge (1990). "Diethyl [(2-Tetrahydropyranyloxy)methyl]phosphonate". Organic Syntheses; Collected Volumes, vol. 7, p. 160.
^ 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.

[1] Paul Ch. Kierkus (2001). "3,4-Dihydro-2H-pyran". EEROS. doi:10.1002/047084289X.rd230. ISBN 0471936235.

[2] R. L. Sawyer and D. W. Andrus (1955). "2,3-Dihydropyran". Organic Syntheses; Collected Volumes, vol. 3, p. 276.

[3] R. A. Earl L. B. Townsend (1990). "Methyl 4-Hydroxy-2-butynoate". Organic Syntheses; Collected Volumes, vol. 7, p. 334.

[4] Arthur F. Kluge (1990). "Diethyl [(2-Tetrahydropyranyloxy)methyl]phosphonate". Organic Syntheses; Collected Volumes, 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.

[1]

[2]

[3]

[4]

[5]

Preparation

Reactions

See also

References