Tetrahydrofuran s. a. Furan tetrahydro

A related reaction occurs on irradiation of a hypochlorite (Scheme 2). The alkoxyl radical can again abstract a hydrogen atom in a l,S-shift, and the final chloro alcohol can be cyclized to form a tetrahydro-furan. Some processes lead directly to the cyclic product For instance, an alcohol with an accessible 8-hydrogen can be directly converted to a tetrahydrofuran on refluxing with lead tetraacetate. In a related reaction, treatment of an alcohol with silver carbonate and bromine can lead to the cyclic ether by initial formation of a hypohalite. The cyclization occurs when the rearranged radical is converted to a cation, either by oxidation with Pb(OAc)4 or by silver-assisted loss of halide ion. Hypoiodites are also fiequent-ly used, generated in situ. ... 

An approach to enantiomerically pure (R)- and (S)-2-(alkenyl)tetrahydrofurans has been devised via a nucleophilic substitution on an allylic complex of palladium(O). This substitution proceeds with chirality transfer from a preexisting stereogenic center to the newly formed center. Thus, starting from (/ )-(,E)-7-methyI-4-octene-l,6-dioI (1), an efficient transfer is realized by treatment with a catalytic amount of tetrakis(triphenylphosphane)palladium in the presence of triethylamine in acetonitrile66. After 30-45 min at 35-37 °C, (5)-tetrahydro-2-f( )-3-methyl-l-butenyl]furan (2) is obtained in 95% yield and 80% ee. The absolute stereochemistry and the optical purity [a]D —10.7 (c = 2.279, CH2C12) are conveniently determined by conversion to the known (S)-tetrahydro-2-furanmethanol. 

Hexene converted to trihexylborane by treatment with borane in tetrahydro-furan, a soln. of diazoacetone in tetrahydrofuran added during ca. 20 min. with stirring and ice-cooling at 20°, stirred 0.5 hr. at room temp., then refluxed 0.5 hr. -> 2-nonanone. Y 65%. - As in other syntheses with organoboranes, only one of the alkyl groups of the intermediate trialkylborane is constructively consumed. F. e. s. J. Hooz and S. Linke, Am. Soc. 90, 5936 (1968) synthesis of diketones s. Chem. Commun. 1969, 139 synthesis of carboxylic acid esters and nitriles s. Am. Soc. 90, 6891 deuterio compounds s. Am. Soc. 91, 6195 (1969). 

Ethereal methyllithium added at -70 to -60° to propargyl chloride in tetrahydro-furan, treated immediately at -70 to -60° with a soln. of tricyclohexylborane prepared from borane and cyclohexene in tetrahydrofuran, allowed to warm to room temp., ether and tetrahydrofuran removed under reduced pressure, the residue treated with acetic acid, and stirred 1 hr. at 25-30° 1-cyclohexyl-1,2-propadiene. Y 77%. F. e. s. T. Leung and G. Zweifel, Am. Soc. 96, 5620 (1974). 

M -butyllithium in hexane added to a soln. of diisopropylamine in tetrahydro-furan at —20°, stirred at 0° for 15 min, a soln. of startg. N,N-dimethylhydrazone in tetrahydrofuran added, cooled to —78° after 2 h, a mixture of 2-bromoethyl-l,3-dioxolane and HMPA added slowly, warmed slowly to room temp, after 1 h, and stirred for 2 h intermediate (Y 70%), in acetic acid refluxed for 4 h 3-Aj-butyl-pyridine (Y 50%). Alkylation of ketone dimethylhydrazones takes place exclusively at the less-substituted a-carbon, thereby allowing selective preparation of 2- and 3-monoalkyl pyridines. F.e.s. M. Marchetti, J. Heterocyc. Chem. 25, 1761-5 (1988). 

Tripeptides. A soln. of N-carbobenzoxyglycine and triethylamine in tetrahydro-furan cooled to —5°, ethyl chloroformate in tetrahydrofuran added dropwise with stirring, which is continued for 30 min., a soln. of N-trimethylsilyl- -alanine trimethylsilyl ester in tetrahydrofuran added, stirred 90 min. at 5°, 90 min. at room temp., refluxed briefly, cooled, and the above procedure repeated with N-trimethylsilylglycine trimethylsilyl ester, finally treated with aq. NaHCOj N carbobenzoxyglycyl-y9-alanylglycine. Y 76%. F. e. and method s. L. Birkofer, A. Ritter, and P. Neuhausen, A. 659, 190 (1962). 

A mixture of 3/ -acetoxy-5-cholenic acid and N,N -carbonyldiimidazole in dry tetrahydrofuran allowed to stand 1 hr. at room temp., dil. with more tetrahydro-furan, and irradiated 8 hrs. with a medium-pressure Hg-lamp in a quartz immersion well -> 20-methylene-5-pregnen-3/ -ol acetate. Y 64%. F. e. s. S. Iwasaki, Helv. 59, 2753, 2738 (1976). 

Tetrahydrofuran ring. An aq. soln. of l,2-dihydro-2-hydroxy-7-methoxy-czs-l,2-dimethyl-l-(2-dimethylaminoethyl)naphthalene methiodide digested 20 min. with thallous hydroxide on a steam bath -> l,2,3a,9b-tetrahydro-8-methoxy-czs-3a,9b-dimethylnaphtho[24-b]furan. Y 78%.—Thallous hydroxide proved to be superior to silver hydroxide. F. e. s. E. L. May and H. Kugita, J. Org. Ghem. 26,188 (1961). 

Trimethylsilyl can be used in peptide synthesis for blocking of carboxyl as well as for protection of hydroxyl and sulfhydryl. It can be easily removed by treatment with water or alcohol.—E N-Carbobenzoxyglycine warmed 1 hr. at ca. 50° with 10% excess N,N -carbonyldiimidazole in anhydrous tetrahydro-furan, cooled, shaken and treated dropwise with a soln. of N,0-bis (trimethylsilyl) -DL-serine trimethylsilyl ester, refluxed ca. 1 hr., tetrahydrofuran removed by distillation at 12 mm, and treated with water N-carbobenzoxyglycyl-DL-serine. Y 80%. F. e., also with POCI3 (cf. Synth. Meth. 13, 450), s. L. Birkofer, W. Konkol, and A. Ritter, B. 94, 1263 (1961) N.N -carbonyldiimidazole method s. Synth. Meth. 14, 452. 

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