Anhydro preparation

Decomposition of the diazoimide (551) by heating in the presence of copper acetylaceton-ate also generated a ketocarbene (552). This undergoes an intramolecular condensation to give the anhydro-4-hydroxy-3-methyl-4-p-nitrophenyl-2-phenyloxazolium hydroxide (553), which cannot be prepared by more classical means (75CL499). 

Zl -Pyrrolines have been isolated from the hydrogenation products of y-ketonitriles (23-26) and in a large number of reactions during which enamino ketones are formed as intermediates. The preparation of pyrrolines from anhydro-5-hydroxyoxazolinium hydroxides (13, R, R" = Ph, R = Me) is also important (27). By the reaction of 13 with styrene, l-methyl-2,3,5-triphenyl-/l -pyrroline (14) is formed. 

That alkylation of the anhydro-bases takes place at the indole nitrogen atom in the jS-carboline series was established conclusively by the identity of the product (429), prepared by treatment of pyr-N-ethyl-jS-carboline anhydro-base (428) with ethyl iodide, with 2,9-diethyl-jS-carbolinium iodide (429) obtained from the reaction of imi-A-ethyl-jS-carboline (430) with ethyl iodide (see Section IV, A, 2). 

Deoxy-D-jcylo hexose 6-(dihydrogen phosphate) (21) has also been synthesized (2) the reaction sequence makes use of 3-deoxy l 2,5 6-di-O-isopropylidene D-galactofuranose (16), a compound that can be easily prepared from D-glucose (2, 60). The mono-isopropylidene derivative (17) formed by partial hydrolysis of the di-ketal is converted into the 6-tosylate (18) by reaction with one molar equivalent of p-toluenesulfonyl chloride. From this the epoxide (19) is formed by reaction with sodium methoxide. Treatment of the anhydro sugar with an aqueous solution of disodium hydrogen phosphate (26) leads to the 6-phosphate (20)... 

Likewise, complete synthesis of acarbose was conveniently accomplished by use of the anhydro derivative 392b prepared from maltotriose. Condensation of 392b with optically active 359 afforded two products, one of which was, after deprotection, shown to be identical to an authentic sample of acarbose. 

C-Glycosyl derivatives may be prepared by utilizing glycosyl fluorides. Ishido and coworkers reported that the reaction of 2,3,5-tri-O-benzyl-a-(36a) or - -D-ribofuranosyl fluoride (36fi) with isopropenyl trimethylsilyl ether under BF3 catalysis (0.1 -0.05 mol. equiv. for the fluoride, in ether or acetonitrile) gave a mixture of 4,7-anhydro-5,6,8-tri-C)-benzyl-l,3-dideoxy-D-altro- (139, major) and -D-a//o-2-octulose (140) 139 was stated to isomerized to 140 (should be vice versa) under Lewis acid catalysis. Similar... 

The 4-triflates 277, 279, and 281 of benzyl 2,3-anhydro-o -D- and -) -L-ri-bopyranosides and -a-D-lyxopyranoside gave, - readily, on reaction with BU4NF [CgHg (24 h) or MeCN (5-8 h), r.t.], the respective 2,3-anhydro-4-deoxy-4-fluoro derivatives 278,280, and 282 in good yields. The conformation ( //s) of the starting compounds remained the same after fluorination. Methyl 2,3-anhydro-4-deoxy-4-fluoro-a-L-lyxopyranoside (284, 86%) was prepared from the 4-triflate 283 by treatment with EtjN- 3HF (CH2CI2-EtjN, 40°, 5 h). 

Trideoxy-2,3,4-trifluoro-D-galacto- and -gluco-pyranosyl derivatives 391 and 392 have been prepared from l,6-anhydro-4-(9-benzyl-2-deoxy-2-fluoro-/ -D-glucopyranose (385) by use of DAST, through several intermediates, as shown [385 386,10% 387- 388,72% 389 390,90% refl. toluene (for 385) or dichloromethane (for 387 and 389), 24 h]. 

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