And the Kiliani-Fischer synthesis

Note that the Wohl degradation and the Kiliani-Fischer synthesis are conceptually opposite transformations. 

Both Fischer projections and the Kiliani-Fischer synthesis are named after Emil Fischer, a noted chemist of the late nineteenth and early twentieth centuries, who received the Nobel Prize in Chemistry in 1902 for his work in carbohydrate chemistry. Fischer s most elegant work is the subject of Section 27.11. 

Show the common reactions of monosaccharides that were presented in this chapter oxidation with nitric acid oxidation with bromine reduction with sodium borohydride esterification glycoside formation and the Kiliani-Fischer synthesis. 

The Kiliani-Fischer synthesis accomplishes the opposite of the Ruff degradation. Ruff degradation of either of two C2 epimers gives the same shortened aldose, and the Kiliani-Fischer synthesis converts this shortened aldose htack into a mixture of the same two C2 epimers. For example, glucose and mannose are degraded to arabinose, and the Kiliani-Fischer synthesis converts arabinose into a mixture of glucose and mannose. 

The Ruff degradation and the Kiliani—Fischer synthesis allow us to place all of the aldoses into families or family trees based on their relation to D- or L-glyceraldehyde. Such a tree is constructed in Fig. 22.7 and includes the structures of the D-aldohexoses, 1-8. 

The addition of cyanide to the aldehydic carbon of polyhydroxyaldehydes (see Carbohydrates, Chapter 11, and the Kiliani-Fischer synthesis) and simple aldehydes... 

The range of transformations achievable through hydrolysis of [ C]cyanohydrins includes the formation of a-hydroxy or a,/3-unsaturated [l- C]carboxylic acids and the Kiliani-Fischer synthesis of [l- C]aldoses. In the former, simultaneous acid-catalyzed... 

Just as the Kiliani-Fischer synthesis lengthens an aldose chain by one carbon, the Wohl degradation shortens an aldose chain by one carbon. The Wohl degradation is almost the exact opposite of the Kiliani-Fischer sequence. That is, the aldose aldehyde carbonyl group is first converted into a nitrile, and the resulting cyanohydrin loses HCN under basic conditions—the reverse of a nucleophilic addition reaction. 

A sequence known as the Kiliani-Fischer synthesis was developed primarily for extending an aldose chain by one carbon, and was one way in which configurational relationships between different sugars could be established. A major application of this sequence nowadays is to employ it for the synthesis of " C-labelled sugars, which in turn may be used to explore the role of sugars in metabolic reactions. 

The Kiliani-Fischer synthesis lengthens the carbon chain of an aldose by one carbon at the aldehyde end and forms a new aldose with its corresponding epimers. When glucose and its epimer are produced from the corresponding pentose via the Kiliani-Fischer synthesis, and then both epimers are reacted with dilute nitric acid, both form optically active compounds. 

Which of the following pentoses, when undergoing the Kiliani-Fischer synthesis, will yield D-glucose and D-mannose ... 

D-(+)-glyccraldchyde was allowed to undergo the Kiliani-Fischer synthesis. and the reaction ran to completion. After separation of any isomers, how many optically active products were formed ... 

The final reaction to be covered in this section is known as the Kiliani-Fischer synthesis. It is a method that converts an aldose to two diastereomeric aldoses that contain one more carbon than the original sugar. The Kiliani-Fischer synthesis is illustrated in the following reaction sequence, which shows the formation of the aldopentoses D-ribose and D-arabinose from the aldotetrose D-erythrose ... 

Application of the Kiliani-Fischer synthesis to the aldopentose D-arahinose produces aldohexoses D-glucose and D-mannose. Because the Kiliani-Fischer synthesis incorporates the stereocenters of D-arabinose without changes, D-glucose and D-mannose must have the same configurations at carbons 3,4, and 5 as does D-arabinose at carbons 2, 3, and 4, respectively. Furthermore, D-glucose and D-mannose must differ only in their configuration at carbon 2. 

The Kiliani-Fischer synthesis accomplishes the opposite of the Ruff degradation. Ruff degradation of either of two C2 epimers gives the same shortened aldose, and the... 

Ruff degradation of D-arabinose gives D-erythrose. The Kiliani-Fischer synthesis converts D-erythrose to a mixture of D-arabinose and D-ribose. Draw out these reactions, and give the structure of D-ribose. 

The Kiliani-Fischer synthesis lengthens a carbohydrate chain hy adding one carhon to the aldehyde end of an aldose, thus forming a new stereogenic center at C2 of the product. The product consists of epimers that differ only in their configuration about the one new stereogenic center. For example, the Kiliani-Fischer synthesis converts D-arabinose into a mixture of D-glucose and D-mannose. 

Because the Kiliani-Fischer synthesis forms two epimers at C2, glucose and mannose have the same configurations at three stereogenic centers (C3-C5), but opposite configurations at C2. Thus, glucose and mannose are either 1 and 2,3 and 4,5 and 6, or 7 and 8. 

We can now narrow down the possible structures for arabinose, the aldopentose that forms glucose and mannose from the Kiliani—Fischer synthesis (Fact [1]). 

A D-aldohexose A is formed from an aldopentose B by the Kiliani-Fischer synthesis. Reduction of A with NaBH4 forms an optically inactive alditol. Oxidation of B forms an optically active aldaric acid. What are the structures of A and B ... 

Identify compounds A-D. A D-aldopentose A is oxidized with HNO3 to an optically inactive aldaric acid B. A undergoes the Kiliani-Fischer synthesis to yield C and D. C is oxidized to an optically active aldaric acid. D is oxidized to an optically inactive aldaric acid. 

The addition of HCN to aldehydes has been a well-known reaction since the 19th century, especially in the context of the Kiliani-Fischer synthesis of sugars. Even older is the Strecker synthesis of amino acids by simultaneous reaction of aldehydes with ammonia and HCN followed by hydrolysis. The challenge in recent years has been to achieve face-selectivity in the addition to chiral aldehydes. These face-selective additions, known as nonchelation-controlled processes, refer to the original formulation of Cram s for the reaction of nucleophiles with acyclic chi carbonyl compounds. The chelation-controlled reactions refer also to a formulaticxi of Cram s, but whose stereochemical consequences sometimes differ. 2... 

Cyanohydrins derived from aldehydes are generally more stable than those from ketones (Ternay, 1976). Cyanohydrin formation is the first step in the well-known chain-lengthening sequence, the Kiliani-Fischer synthesis. For example, D-arabinose, an aldopentose, ultimately affords both o-glucose and D-mannose by this set of reactions (Carey, 2000b). 

---