Koenigs-Knorr

Although the Koenigs-Knorr reaction appears to involve a simple backside S 2 displacement of bromide ion by alkoxide ion, the situation is actually more complex. Both a and /3 anomers of tetraacetyl-o-glucopyranosyl bromide give the same /3-glycoside product, implying that they react by a common pathway. 

Figure 25.6 Mechanism of the Koenigs-Knorr reaclion, showing the neighboring-group effect of a nearby acetate.

The participation shown by the nearby acetate group in the Koenigs-Knorr reaction is referred to as a neighboring-group effect and is a common occurrence... 

Koenigs-Knorr reaction (Section 25.6) A method for the synthesis of glycosides by reaction of an alcohol with a pyranosyl bromide. 

Koenigs-Knorr reaction of, 990 molecular model of, 119, 126, 985 mutarotation of, 985-986 pentnacetyl ester of, 988 pentamethyl ether of, 988 pyranose form of, 984-985 pyruvate from. 1143-1150 reaction with acetic anhydride, 988 reaction with ATP, 1129 reaction with iodomethane, 988 sweetness of. 1005 Williamson ether synthesis with. 988... 

El reaction and, 392 E2 reaction and, 386 S l reaction and, 373-374 Sjxj2 reaction and, 362-363 Kishner, N. L. 715 Knoevenagel reaction, 913 Knowles, William S., 734, 1027 Kodel, structure of, 1222 Koenigs-Knorr reaction, 990 mechanism of, 990 neighboring-group effect in, 990-991... 

In the Koenigs-Knorr method and in the Helferich or Zemplen modifications thereof, a glycosyl halide (bromide or chloride iodides can be produced in situ by the addition of tetraalkylammonium iodide) is allowed to react with a hydrox-ylic compound in the presence of a heavy-metal promoter such as silver oxide, carbonate, perchlorate, or mercuric bromide and/or oxide,19-21 or by silver triflu-oromethanesulfonate22 (AgOTf). Related to this is the use of glycosyl fluoride donors,23 which normally are prepared from thioglycosides.24... 

The synthesis93 of N-(2,4-dinitrophenyl)-3-0-(tetra-0-acetyl-/ -D-glu-copyranosyl)-L-threonine methyl ester (131) involved a two-step procedure. First, formation of the intermediate, L-threonine orthoester 130 was achieved by treatment of tetra-O-acetyl-a-D-glucopyranosyl bromide (128) with the methyl ester of N-(2,4-dinitrophenyl)-L-threonine94 (129) under the conditions of the Koenigs-Knorr reaction (see next paragraph), and this was then converted into the L-threonine glycoside 131. 

Lindberg and associates103 105 applied the Koenigs - Knorr procedure to the synthesis, from 138 and 139, of 3-0-/ -D-xylopyranosyl-L-serine103 (140), which constitutes the carbohydrate-protein linkage in such pro-... 

Although various modifications of the Koenigs-Knorr procedure were used by these workers, the best overall yields of the O-deacetylated glycopeptide derivatives were only 5 to 10%. 

The disaccharide derivatives 196 and 197 of N-tosyl-L-serine, of interest for the study of D-galactose-binding lectins, were prepared by Kaifu and Osawa148 from 194 and 195, respectively, by protection of 0-4 and -6 with a benzylidene group, condensation of the acetal with tetra-O-acetyl-a-D-galactopyranosyl bromide (110) under Koenigs-Knorr conditions, and deprotection. 

From a historic perspective glycosyl chlorides and bromides introduced, respectively, by Michael [2] and Koenigs and Knorr [3] were the most widely used donors in the saccharide synthesis for a very long time. The introduction of 1,2-orthoesters in 1964 [4] was the first important attempt to find an alternative to the Koenigs-Knorr method. However, Paulsen in his 1990 review of reliable donors for glycosyl... 

Carbohydrate orthoesters, first reviewed by Pacsu more than 60 years ago [8], were reported by Fischer et al. [9] as by-products of the Koenigs-Knorr reaction [3] of acetobromo-L-rhamnose (1) with methanol. Orthoacetate 3 was isolated along with the expected a- and P-methyl rhamnosides 2 (Scheme 5.2). However, its true structure was assigned only 10 years later by several research groups [10-12]. 

Kodel, 20 33, 37 Koenigs-Knorr reaction, 4 704 Kogenate, cell culture technology product, 5 346t... 

The Koenigs-Knorr method in the presence of an insoluble silver salt proceeds mainly with inversion of configuration. Silver silicate and silver-silicate-aluminate have often been used as the heterogeneous catalyst. This procedure has been traditionally used for the synthesis of p-mannosidcs and has been recently reviewed.35 However, it only works well with very reactive halides and sufficiently reactive alcohol components. 

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