Japp-Klingemann cleavag

Eistert, B., Regitz, M. Japp-Klingemann cleavages. I. Cleavage of the coupling products of p-nitrobenzenediazonium chloride with carboxylic acid esters of tetrahydrothiopyran-3-one and thiophan-3-one. Ann. 1963, 666, 97-112. 

Jacobsen reaction 19, 611 Japp-Klingemann cleavage 7,406 19,28,185 Jones reagent (chromium trioxide-sulfuric acid-acetone) 2, 289 12, 335... 

Selective hydrolysis s. 19, 27 a-Ketosulfone hydrazones from a-azo- -ketosulfones Japp-Klingemann cleavage also ring opening s. 19, 28 Garbamyl disulfides from dithioformimidic acid esters s. 16,626... 

Dihalogenomethylenehydrazines from 1,2,3-triketone 2-monohydrazones via Japp-Klingemann cleavage of a-azo-a,c(-dihalogenoketones... 

Ring opening of a-azocycloketones Japp-Klingemann cleavage... 

SO the product in this case is also the hydrazone, and not the azo compound. In fact, compounds of the type 16 are seldom isolable from the reaction, though this has been accomplished. The cleavage step shown is an example of 12-41 and, when a carboxyl group cleaves, of 12-38. The overall process in this case is called the Japp-Klingemann reaction and involves conversion of a ketone (17) or a carboxylic... 

Larger amounts of pyridine drastically enhanced the coupling reaction and loading of 118, but also led to an increased formation of Japp-Klingemann type by-products 120. Several procedures to transform the diazonium salts into traceless products were explored before the formation of pure (3-lactams. The best conditions for traceless cleavage turned out to be simplified Keumi conditions [147]. (Scheme 37-38)... 

Enolates of P-dicarbonyl and similar doubly activated compounds are aminated by aryldiazonium salts to give hydrazones by rearrangement of the intermediate azo compounds.14,15,615,616 The Japp-Klingemann reaction617,618 is a variation in which either acyl cleavage or decarboxylation occurs in situ after the amination. The hydrazones may be reduced to amines 619... 

Serotonin has been synthesised by several routes the method shown relies on a Fischer indole synthesis, the requisite aryl-hydrazone being constructed by a process known as the Japp-Klingemann reaction in which the enol of a 1,3-dicarbonyl compound is reacted with an aryl-diazonium salt, with subsequent cleavage of the 1,3-dicarbonyl unit. 

Formation of a C-N bond with cleavage of a C-C bond occurs occasionally as undesired side reaction during nitration,166,1183 nitrosation, or azo coupling. Some examples of this have been mentioned in the respective Sections. Such reactions have preparative interest only when they form the main reaction, as in the Japp-Klingemann reaction (see page 436) and in certain oximations by nitrous acid (see page 429). 

A. P. Kozihowski and W. C. Floyd. Borohydride reduced cleavage of azo derivatives of j3-keto esters. A useful variant of the Japp-Klingemann reaction for C-nucleoside synthesis. Tetrahedron Letters, 1978,1, 19. 

---