Hydrogen cyanide, addition

1 Benzoin Condensation. The benzoin condensation is a related reaction consisting of treating an aromatic aldehyde with potassium cyanide or sodium cyanide usually in an aqueous ethanolic solution. Breslow studied the effects of inorganic salts on the rate 

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The presence of an aldehyde function m their open chain forms makes aldoses reactive toward nucleophilic addition of hydrogen cyanide Addition yields a mixture of diastereo meric cyanohydrins... 

Racemic pantolactone is prepared easily by reacting isobutyraldehyde (15) with formaldehyde ia the presence of a base to yield the iatermediate hydroxyaldehyde (16). Hydrogen cyanide addition affords the hydroxy cyanohydria (17). Acid-cataly2ed hydrolysis and cyclization of the cyanohydria (17) gives (R,3)-pantolactone (18) ia 90% yield (18). 

When, in 1832, Wohler and Liebig first discovered the cyanide-catalyzed coupling of benzaldehyde that became known as the benzoin condensation , they laid the foundations for a wide field of growing organic chemistry [1]. In 1903, Lapworth proposed a mechanistical model with an intermediate carbanion formed in a hydrogen cyanide addition to the benzaldehyde substrate and subsequent deprotonation [2]. In the intermediate active aldehyde , the former carbonyl carbon atom exhibits an inverted, nucleophilic reactivity, which exemplifies the Umpo-lung concept of Seebach [3]. In 1943, Ukai et al. reported that thiazolium salts also surprisingly catalyze the benzoin condensation [4], an observation which attracted even more attention when Mizuhara et al. found, in 1954, that the thiazolium unit of the coenzyme thiamine (vitamin Bi) (1, Fig. 9.1) is essential for its activity in enzyme biocatalysis [5]. Subsequently, the biochemistry of thiamine-dependent enzymes has been extensively studied, and this has resulted in widespread applications of the enzymes as synthetic tools [6]. 

The benzoin condensation catalyzed by N-heterocyclic carbenes has been investigated intensively. First investigations date back to 1832 when Wohler and Liebig discovered the cyanide-catalyzed coupling of benzaldehyde to benzoin (Wohler and Liebig 1832). In 1903 Lapworth postulated a mechanism for this reaction in which an intermediate car-banion is formed by hydrogen cyanide addition to benzaldehyde fol-... 

If a vinylic double bond is connected to the bicyclic skeleton of norbomene, a competition experiment shows that under the conditions employed hydrogen cyanide addition proceeds only at the endocyclic strained double bond. It is also noted that isomerization of the exocyclic olefinic bond may take place in the course of the reaction [22, 23, 37]. These experiments already reveal the most important features of homogeneously catalyzed hydrocyanation - the influence of the steric structure of the substrate and the fact that the catalyst also promotes isomerizations (cf. Section 2.5.5.1). 

Jackson, W.R. and Lovel, C.G. 1982. The stereochemistry of metal catalyzed hydrogen cyanide addition to alkenes. Tetrahedron Letters, 23 1621-1624. 

Unstable and hitherto unknown 2-azanorbornadiene has been generated, and its presence has been characterized spectroscopically. Its instability is due to a retro Diels-Alder reaction leading to cyclopentadiene and hydrogen cyanide. Addition of PTAD accelerated the retro reaction, and instantaneous quantitative formation of the Diels-Alder adduct of cyclopentadiene and PTAD proved the process (91TL6957). 

On heating (150 °C, 10 h) [Fe(CNMe)6]Cl2 is converted to a mixture of cis- and trans-[FeCl2(CNMe)4]. Somewhat surprisingly, [H4Fe(CN)j] reacts with aliphatic alcohols to form [Fe(CN)2(CNR)4] and other complexes. Intermediate species formed during this reaction can polymerize with the evolution of hydrogen cyanide. Addition of HCN displaces isocyanide, however, and so constitutes a catalytic cycle for the synthesis of RNC from HCN and ROH. 

Cyanohydrin NC — RR COII, the product of hydrogen cyanide addition to the carbonyl group. 

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