Photochemical approach to functionalized naphtho[2,1-d]oxazoles and heterobenzoxazoles

U ovom radu pripravljen je niz 4-(aril/heteroariletenil)oksazola 2-7, skupine spojeva strukturno sličnih stilbenu u čijoj strukturi je jedna benzenska jezgra zamijenjena oksazolskim prstenom, sintetiziranih Wittigovim reakcijama iz 2-metil-oksazol-4-karbaldehida (1) uz odgovarajuće fosfonijeve soli. Aldehid 1 dobiven je redukcijom iz odgovarajućeg oksazolskog estera, metil-2-metiloksazol-4-karboksilata. Sintetizirani derivati oksazola su 4-(2-(furan-2-il)vinil)-2-metiloksazol (2), 2-metil-4-(2-(tien-2-il)vinil)oksazol (3), 2-metil-4-(4-metoksistiril)oksazol (4), 2-metil-4-(4-nitrostiril)oksazol (5), 2-metil-4-(2-cijanostiril)oksazol (6) i 2-metil-4-(4-metilstiril)oksazol (7). Osim primjene fosfonijevih soli u reakciji sinteze oksazolskih derivata korišten je i TOSMIC, reagens koji zbog svojih reaktivnih skupina olakšava raspon transformacija zbog čega postaje široko primjenjivan u organskoj kemiji. Primjenom 4-dimetilamino-cimtaldehida (a), 4-fluor-cimtaldehida (b) i 4-klor-cimtaldehida (c) u reakciji s K2CO3, MeOH i TOSMIC reagensom kao produkt također dobivamo 4-(aril/heteroariletenil)oksazole 8-10. Sintetizirani derivati oksazola su 4-(2-dimetilaminostiril)oksazol (8), 5-(4-fluorstiril)oksazol (9) i 5-(4-klorstiril)oksazol (10). Sintetizirani novi derivati 4-(aril/heteroariletenil)oksazola 4-10 podvrgnuti su fotokemijskim reakcijama ciklizacije, na 300 nm ili 350 nm u otopini toluena uz dodatak joda pri čemu su kao produkti nastali novi ciklički derivati naftoksazola. Sintetizirani naftoksazolski derivati su 2-metil-8-metoksinafto[2,1-d]oksazol (11), 2-metil-8-nitronafto[2,1-d]oksazol (12), 2-metil-nafto[2,1-d]oksazol-6-karbonitril (13), 8-dimetilaminonafto[2,1-d]oksazol (14), 8-fluornafto[2,1-d]oksazol (15), 2-metil-8-metilnafto[2,1-d]oksazola (16) i 8-klornafto[2,1-d]oksazol (17). Početni spojevi 4-(aril/heteroariletenil)oksazola 2-10 i spojevi 11-17 nastali kao fotoprodukti fotokemijske ciklizacije, pročišćeni su kolonskom kromatografijom i dobiveni uiskorištenjima od 30-77%. Također, svaki izolirani spoj okarakteriziran je spektroskopskim metodama.In this work, there are prepared a series of 4-(aryl/heteroarylethenyl) oxazoles 2-7, structurally similar to stilbene compounds where one benzene core is replaced by an oxazole ring, and synthesized by Wittig reaction from 2-methyloxazole-4-carbaldehyde (1) and suitable phosphonium salts. Aldehyde 1 was obtained by reduction of the corresponding oxazole ester, methyl 2-methyloxazole-4-carboxylate. Synthesized and isolated oxazole derivatives are 4-(2-(furan-2-yl) vinyl)-2-methyloxazole (2), 2-methyl-4-(2-(thien-2-yl) vinyl)oxazole (3), 2-methyl-4-(4-methoxystyryl)oxazole (4), 2-methyl-4-(4-nitrostyryl) oxazole (5), 2-methyl-4- (2-cyanostyryl) oxazole (6) and 2-methyl-4-(4-methylstyryl) oxazole (7). Apart from the application of phosphonium salts in photochemical cyclization, TOSMIC is also used as areagent which, because of its reactive groups, facilitates the range of transformations making it widely applicable in organic chemistry. Using 4-dimethylamino-cinnamaldehyde (a), 4-fluoro-cinnamaldehyde (b) and 4-chloro-cinnamaldehyde (c) in reaction with K2CO3, MeOH and TOSMIC reagent, as a product are also prepared new 4-(aryl/heteroarylethenyl) oxazoles 8-10. The synthesized oxazole derivatives are 4-(2-dimethylaminostyryl) oxazole (8), 5-(4-fluorostyryl)oxazole (9) and 5-(4-chlorostyryl)oxazole (10). 4-(aryl/heteroarylethenyl) oxazole derivatives 4-10 are subjected to photochemical cyclization reactions at 300 nm or 350 nm in a toluene solution with the addition of iodine, where are produced new derivatives of naphthoxazole as photochemical products. The synthetized and isolated naphthoxazole derivatives are 2-methyl-8-methoxynaphtho[2,1-d]oxazole (11), 2-methyl-8-nitronaphtho [2,1-d]oxazole (12), 2-methylnaphtho[2,1-d]oxazole-6-carbonitrile (13), 8-dimethylaminonaphtho[2,1-d] oxazole (14), 8-fluoronaphtho[2,1-]oxazole (15), 2-methyl-8-methylnaphtho[2,1-d] oxazole (16) and 8-chloronaphtho[2,1-d]oxazole (17). All new compounds 4-(aryl/heteroarylethenyl) oxazole 2-10 and and their new photoproducts of cyclization 11-17 are purified by column chromatography in the moderate-to-good yields of 30-77%. Also, every new compound is characterized by spectroscopic methods