Prepn. of oxygen heterocyclics of formula (I) comprises cyclisation of phosphonium salts (IIe in the liquid phase in the presence of a base. In the formulae, is an aromatic ring esp. benzene, opt. substd. by oxonitro, hydroxy, halo or organic radicals such as those of R1, R3, R10, r10 O-R10CO, R10COO or R10OOC-, D is -CHR3-O- or -O-, R1, R3 are H, lower alkyl, aryl, aralkyl or cycloalkyl and when D is -CHR3-O- then R1 and R3 may be an organic radical, R2 is H or an organic radical (pref. R10, R10O-), R10 is alkyl, alkenyl, alkynyl, aryl, aralkyl, aralkenyl, aralkynyl or cycloaliphatic, R1 is alkyl, aryl or aralkyl, and X- is an anion. (I) are cpds. such as benzofurnas, chromene and isochromenes which have numerous known uses such as vasodilators (e.g. khellinone), spasmolytics, antibacterials (e.g. 2-(p-nitrophenyl)-benzofuran), parasiticides, stimulants, tranquillisers, endocrine active agents, herbicides, phytohormones, photosensitisers (e.g. psoralene, methoxsalene and trioxsalene) and intermediates. The process is partic. useful for the prepn. of benzofurans, providing a general synthesis, which may give improved yields and allow prodn of cpds. inaccessible by known synthetic routes.
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