Koenigs-Knorr reactions

SCHEME 1.3 Early examples of chemical glycosylations. (a) The first reported chemical glycosylation. (b) A Koenigs-Knorr reaction. Ac, acetyl. 

FIGURE 1.12 The first identified branched-chain sugar, hamamelose. 

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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. 

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... 

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. 

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... 

A number of glycosides were available to Fischer by way of the Koenigs-Knorr reaction and his own glycoside synthesis, which involves treatment of... 

Most of the methods available for the synthesis of this class of compoimd have been referred to in the preceeding pages. These include the modified Koenigs-Knorr reaction (p. 406), the use of glycosyl halides with non-... 

A second method is based on the abnormal course of the Koenigs-Knorr reaction with fluoroalkyl alcohols. Indeed, when there are two or three methylenes between the Rf group and the hydroxyl, the reaction does not lead to substitution of the anomeric bromide but instead affords an orthoester. In the presence of mercuric bromide, this orthoester can undergo a rearrangement into an (9-fluoroalkyl glycoside (Figure 6.47). 

M. Dejter-Juszinsky and H. M. Flowers, Koenigs-Knorr reaction. 11—synthesis of an oi-L-linked disaccharide from tri-O-benzyl-L-fucopyranosyl bromide, Carbohydr. Res. 18 219 (1971). 

K. Igarashi, The Koenigs-Knorr reaction, Adv. Carbohydr. Chem. Biochem. 34 243 (1977). 

Koenigs-Knorr reaction is carried out using simple, liquid aglycons (methanol or ethanol, for example), the alcohol also serves as the solvent for the halide, and is frequently present in large excess. In such cases, the halide is rapidly converted into glycoside, and the water formed in the secondary reaction between the liberated hydrogen halide and silver carbonate is seldom cause for concern. 

An aglyconic derivative of KDO, having 0-7 and 0-8 temporarily blocked, was required for the synthesis of the model disaccharide Koenigs-Knorr reaction of 3 with a suitable halide derivative of KDO would be expected to occur exclusively at the (equatorial) 0-4 while 0H-5, being axially-disposed and experiencing additional steric shielding by H-7, would be practically unreactive. X-ray crystal structure analysis of KDO derivatives (14, 15) has shown that H-7 is orient-... 

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