Synthesis of substituted dibenzophospholes. Part 8. Synthesis and resolution of atropisomers of a 4,6-diaryldibenzophosphole

Abstract

Regiospecific replacement of the 4″- and 6′-nitro groups in a 2′,2″,4″,6′-tetranitro-m-quaterphenyl by alkoxy groups has been effected in two ways: (i) the dialkali salts of α-oximinoalkanoic acids replaced one nitro group by a hydroxy group; after O-alkylation the other alkoxydenitration was effected by sodium benzaldehyde oxime followed by O-alkylation; (ii) both nitro groups were replaced by treatment with sodium 2,2-dimethoxy-1,2-diphenylethanone oximate followed by acidic hydrolysis, alkaline cleavage, and O-alkylation. From the product, synthetic procedures already developed gave 3,7-di-isopropoxy-5-methoxy-4,6-bis-(4-methoxy-2-methyl)dibenzophosphole 5-oxide, separated by chromatography into one racemic and two meso forms. The thermal interconversion of the three forms was demonstrated and measured. The racemic form was resolved by high-performance liquid chromatography (h.p.l.c.) on a chiral column.