Ian J. Fletcher

Olefin Synthesis with Anils

Publisher Summary This chapter presents the sequence of reactions involved in the preparation of heteroaromatic stilbenes by direct condensation of methyl or methylene groups with anils derived from aromatic aldehydes, in the presence of strong base, and in certain dipolar aprotic solvents. Both 2-( p -tolyl)-5- phenylthiazole and 2-( p -tolyl)benzothiazole can be converted to the corresponding stilbene derivatives by reaction with aromatic aldehyde anils under the influence of potassium hydroxide. Pyrazoles substituted in the 1-, 3-, or 5-position with a p -tolyl group are converted to the corresponding stilbenyl derivatives, with benzalanilines in the presence of potassium hydroxide, only in very low yield. The use of aniles in the synthesis of triazoles and condensed triazoles including 2 H -1,2,3-triazoles and 1,2,4-triazoles; and benzotriazoles, naphtho[1,2- d ]triazoles, and benzo[1,2- d :3,4- d′ ]bis-triazoles, are also presented in the chapter. The reactions of nitrogen-containing six-membered rings including (1) pyridines, (2) pyrimidines, (3) 1,2,4- and 1,3,5-triazines, (4) quinazolines, and (5) quinoxalines, are discussed in the chapter. A further use of anils in the synthesis of heterocyclic compounds including pyronocoumarins, pyrono-2-quinolones, and dihydroquinolines is also discussed in the chapter.

1,3-Dipolar character of six-membered aromatic rings. Part 52. 2π+ 8π Cycloaddition reactions of 1-substituted 3-oxidopyridinium betaines

Dichloroketen and a series of aryl(bromo)ketens react with various 1-substituted 3-oxidopyridiniums to give novel bicyclic compounds by addition across the C(4)–O and the C(2)–O positions. Frontier-MO theory is used to rationalise the orientation of these cycloadditions. Acid-catalysed hydrolysis of the C(2)–O adducts (9) yielded 3-hydroxy-2-benzylpyridines.