The synthesis of methoxy-2-hydroxy-1,4- naphthoquinones and their reaction with aliphatic aldehydes under basic conditions.

Abstract

Although literature reports on the synthesis of variously substituted 2-hydroxy-1 ,4- naphthoquinones appeared to be reasonable; in our hands difficulty was experienced in duplicating much of the work. In order to address this problem, two protocols were used with the one involving conversion of substituted a-tetralones into hydroxyquinones using a solution of the tetralones in an oxygenated solution of tertiary butyl alcohol containing potassium tertiary butoxide, and the other involving Diels-Alder Condensation, oxidation, pyrolysis and basic hydrolysis of a 2-methoxy-1,4-naphthoquinone 79 into the corresponding 2-hydroxy analogue 80. Condensation reaction between 2-hydroxyy-8-methoxy-1,4-naphthoquinone 80 and caproaldehyde 111, produced the 3-alkenyl analogue 115 which was cyclised to the corresponding naphtho[2,3-b ]pyrenquinone 116 and eventually reduced to 8- methoxynaphtho[2,3-b ]pyran-5, 10-dione 1) 7. Condensation between 2-hydroxynaphthoquinone 80 and 4-dioxolanopentanal under basic conditions afforded the desired adduct which was cyclised with dichlorodicyanobenzoquinone, reduced and then hydrolysed with acid to produce 2- acetyl-3,4-dihydronaphtho[2,3-b ]pyran-5, 10-dione 125. By the employment of an alternative sequence of events, the corresponding 4-hydroxy analogue of the above 2- acetylnaphthopyrandione 125 was also prepared for evaluations. Finally condensation between 2-hydroxy-8-methoxy-1,4-naphthoquinone 80 and 5- dioxolanohexanal 128 under basic conditions afforded the 3-hexenyldioxolano 129 derivative, which was cyclised to the naphthopyrene 130 but the yields were disappointing in this instance.