Introduction

As the supply of GBL quickly diminishes, the desire to find a synthesis of GBL from tetrahydrofuran (THF) increases.

Just to make this a more thorough study, here are a few more ref's for a few more procedures worth looking at. I think you'll like them; the oxidation of THF into butyrloactone is a classic, and is the basis of a huge number of studies. Enjoy. Gratis a Beilstein magnificum.

Bibliography

Reaction 1 (sodium bromate)

Reagent: NaBrO₃
Catalyst: 47% HBr
Solvent: CH₂Cl₂
Time: 5 hours
Temp: 35°C
Yield: 67%

Oxidation of Alcohols and Ethers Using Sodium Bromate-Hydrobromic Acid System
Kajigaeshi, Shoji; Nakagawa, Takashi; Nagasaki, Noritaka; Yamasaki, Hiromochi; Fujisaki, Shizuo
Bull. Chem. Soc. Jpn. 59(3), 747-750 (1986)

Reaction 2 (sodium bromate)

Reagent: NaBrO₃, NaHSO₃
Solvent: H₂O
Time: 16.25 hours
Temp: 20°C
Yield: 68%

Oxidation of Diols and Ethers by NaBrO₃/NaHSO₃ Reagent
Sakaguchi, Satoshi; Kikuchi, Daisuke; Ishii, Yasutaka
Bull. Chem. Soc. Jpn. 70(10), 2561-2566 (1997)

Reaction 3 (calcium hypochlorite)

Reagent: Ca(OCl)₂
Solvent: acetic acid, acetonitrile, H₂O
Time: 1 hour
Temp: 0°C
Yield: 68%

The Oxidation of Alcohols and Ethers Using Calcium Hypochlorite
Stephen O.; Keehn, Philip M.
Tetrahedron Lett., No. 23, 35-38 (1982)

Reaction 4 (nitric acid)

Reagent: aqueous HNO₃
Solvent: benzene
Temp: 25°C

Moschkin
Trudy Sovesc. Vopr. Ispolz. Pentozan. Syria Riga; 225, 244 (1955)
Chem. Abstr. 15048 (1959)

Reaction 5 (palladium/oxygen)

Reagent: CO₂-O₂, HCl
Catalyst: PdCl₂-CuCl₂
Temp: 25°C
Pressure: 24 atm

El'man, A. R.; Slivinskii, E. V.; Loktev, S. M.
Bull.Acad.Sci.USSR Div.Chem.Sci. (Engl.Transl.), 37, 1969 (1988)
Izv.Akad.Nauk SSSR Ser.Khim.; RU; 9, 2188-2189 (1988) [In Russian]

Reaction 5 (titanium/hydrogen peroxide)

Reagent: TS-1 (titanium silicate), 30% H₂O₂
Time: 12 hours
Temp: 70°C
Yield: 55%

Catalytic Oxidation of Ethers with H₂O₂ over Zeolites
Sasidharan, M.; Suresh, S.; Sudalai, A.
Tetrahedron Lett. 36, 9071-9072 (1995)

Reaction 6 (Peroxyphosphoric Acid)

Reagent: H₃PO₅
Time: 2 hours
Temp: 25°C
Yield: 34%

Novel Oxidation of Tetrahydrofuran to γ-Butyrolactone with Peroxyphosphoric Acid
Ogata, Yoshiro; Tomizawa, Kohtaro; Ikeda, Toshiyuki
J. Org. Chem. 45, 1320-1322 (1980)

Reaction 9 (manganese(VII) oxide)

Reagent: Mn₂O₇
Solvent: CCl₄, acetone
Temp: -45°C
Yield: 86%

[Selective oxidation of organic compounds with Mn(VII) Oxide]
Troemel, Martin; Russ, Manuel
Angew.Chem. 99(10) 1037-1038 (1987)

Reaction 10 (zinc permanganate)

Reagent: Zn(MnO₄)₂/SiO₂
Solvent: CH₂Cl₂
Time: 0.25 hours
Temp: 20°C
Yield: 51%

Oxidation of organic compounds by zinc permanganate
Wolfe, Saul; Ingold, Christopher F.
J. Amer. Chem. Soc. 105, 7755-7757 (1983)

Reaction 11 (zinc dichromate)

Reagent: ZnCr₂O₇·3H₂O
Solvent: CH₂Cl₂
Time: 1 hour
Temp: 25°C
Yield: 70%

Firouzabadi, H.; Sardarian, A. R.; Moosavipour, H.; Afshari, G. M.
Synthesis, No. 4, 285-288 (1986)

Reaction 12

Reagent: benzyltrimethylammonium tribromide, Na₂HPO₄
Solvent: H₂O
Time: 10 h
Temp: 60°C
Yield: 67%

_{Oxidation Using Quaternary Ammonium Polyhalides. III.}
An Effective Oxidation of Alcohols and Ethers by the Use of Benzyltrimethylammonium Tribromide
Kajigaeshi, Shoji; Kawamukai, Hiroshi; Fujisaki, Shizuo
Bull. Chem. Soc. Jpn. 62(8), 2585-2588 (1989)

Reaction 13 (N-hydroxyphthalimide)

Reagent: N-hydroxyphthalimide
Solvent: pyridine
Yield: 11%
Other Conditions: anodic oxidation

Masui, Masaichiro; Hara, Seijiro; Ueshima, Takahiro; Kawaguchi, Tetsuo; Ozaki, Shigeko
Chem.Pharm.Bull. 31(11), 4209-4212 (1983)

Reaction 14 (benzil/oxygen)

Reagent: benzil, oxygen
Time: 6 hours
Temp: 0°C
Other Conditions: Irradiation

Oxidation of ethers to esters by photo-irradiation with benzil and oxygen
Seto, Hideharu; Yoshida, Keigo; Yoshida, Shigeo; Shimizu, Takeshi; Seki, Hiroshi; Hoshino, Mikio
Tetrahedron Lett. 37(24), 4179-4182 (1996)

Reaction 15 (exotic cobalt reagent)

Reagent: O₂, tris(acetylacetonato)Co(III), 2,3-butanedione
Time: 6 hours
Temp: 50°C
Pressure: 1 atm
Yield: 60%

Hata, Eiichiro; Takai, Toshihiro; Mukaiyama, Teruaki
Chem. Lett., No. 9, 1513-1516 (1993)

Reaction 17 (ruthenium (VIII) oxide)

Reagent: RuO₄
Solvent: CCl₄
Time: 24 hours
Temp: 25°C
Yield: 65%

Smith, Amos B.; Scarborough, Robert M.
Synth. Commun. 10(3), 205-212 (1980)

Reaction 18 (exotic ruthenium reagent)

Reagent: trans-[Ru^VI(N,N'-dimethyl-N,N'-bis(2-pyridylmethyl)propylenediamine)O₂]·[ClO₄]₂
Solvent: acetonitrile
Time: 1 hour
Temp: 25°C
Yield: 98%

Synthesis, Electrochemistry, and Reactivities of trans-[Ru(L)O₂]²⁺
(L = N,N'-dimethyl-N,N'-bis(2-pyridylmethyl)propylenediamine
Che, Chi-Ming; Tang, Wai-Tong; Li, Chi-Keung
J. Chem. Soc. Dalton Trans., No. 12, 3735-3739 (1990)

Reaction 19 (exotic ruthenium reagent)

Reagent: Ru^(V)L(O)²⁺ L = 2-hydroxy-2-(pyridyl)ethyl-bis[2-(2-pyridyl)ethyl]amine
Solvent:Acetonitrile, HClO₄
Temp: 24.9°C
Yield: 80%

Che, Chi-Ming; Ho, Clare; Lau, Tai-Chu
J. Chem. Soc. Dalton Trans. No. 5, 1259-1263 (1991)

Reaction 21 (exotic ruthenium reagent)

Reagent: aq. t-BuOOH
Catalyst: trans-(Ru(H₂O)₂(bipy)₂)·(PF₆)₂·H₂O
Solvent: benzene
Time: 5 hours
Temp: 25°C
Yield: 33%

Bailey, Alan J.; Griffith, William P.; Savage, Paul D.
J. Chem. Soc. Dalton Trans., No. 21, 3537-3542 (1995)

Reaction 22 (exotic Ruthenium reagent)

Reagent: trans-[Ru(VI)(dmpipy)₂O₂]·(ClO₄)₂
Solvent: Acetonitrile
Time: 4 hours
Temp: 25°C
Yield: 85%

Che, Chi-Ming; Leung, Wai-Ho; Li, Chi-Keung; Poon, Chung-Kwong
J. Chem. Soc. Dalton Trans., No.3, 379-384 (1991)

Reaction 23 (exotic Ruthenium reagent)

Reagent: cis-[Ru^VI(6,6'-Cl₂bpy)₂O₂]·ClO₄
Solvent: acetonitrile
Time: 90 min
Temp: 25°C
Yield: 41%

Che, Chi-Ming; Leung, Wai-Ho
J. Chem. Soc. Chem. Commun., No. 18, 1376-1377 (1987)

Reaction 24 (exotic Ruthenium reagent)

Reagent: trans-[Ru(L)O₂]²⁺ (L = sym-Octahydro-14,18-dimethyl-13H-dibenzo-sym-dioxadiazacyclopentadecine
Solvent: trifluoroacetic acid, H₂O
Temp: 24.9°C

Che, Chi-Ming; Tang, Wai-Tong; Wong, Kwok-Yin; Li, Chi-Keung
J.Chem.Soc.Dalton Trans., No. 12, 3277-3280 (1991)

Reverend Drone