Sinteza naftoksazola fotokemijskom ciklizacijom 4-stiriloksazola

In this work photochemical cyclization reactions were studied for stilbene like systems, where one benzene ring is replaced by an oxazole ring. A series of 4-(aryl/heteroarylethenyl)oxazoles 3-10 was synthesized by Wittig reaction from the corresponding oxazole-4-carbaldehyde (1)/2-methyl-oxazole-4-carbaldehyde (2) and diverse phosphonium salts. Aldehydes 1 and 2 were obtained by reduction from the corresponding oxazole esters, ethyl-4-oxazolecarboxylate and methyl-2-methyloxazole-4-carboxylate. The synthesized oxazole derivatives are as follows, 4-(4-methoxystyryl)oxazole (3), 4-(4-methylstyryl)oxazole (4), 4-(2-cyanostyryl)oxazole (5), 4-(4-nitrostyryl)oxazole (6), 4-(4methoxystyryl)-2-methyloxazole (7), 2-methyl-4-(4-methylstyryl)oxazole (8), 4-(2-cyanostyryl)-2-methyloxazole (9) and 2-methyl-4-(4-nitrostyryl)oxazole (10). Photochemical electrocyclization reaction of 4-(aryl/heteroarylethenyl)oxazoles 3-10 gave a series of new naphthoxazoles. The reaction took place at 300 nm or 350 nm, in conditions with oxygen and iodine present, in toluene solution. New naphthoxazole derivatives that were purified are as follows, naphtho[2,1-d]oxazole-6-carbonitrile (13), 8-methylnaphtho[2,1-d]oxazole (14), 8-nitronaphtho[2,1-d]oxazole (15), 8-methylnaphtho[2,1-d]oxazole (16) and 2-methyl-8-methylnaphtho[2,1-d]oxazole (17). All of the new compounds were fully characterized by modern spectroscopic methods (one-dimensional and two-dimensional NMR, UV / Vis and IR).