Syntheses related to some naturally occurring naphthopyranquinones

Bibliography: pages 248-257.The naphtho[2,3-c]pyran ring system occurs not infrequently in Nature as derivatives of the 5,10-quinone. Examples include the eleutherins, the nanaomycins and the protoaphins some of which have been shown to possess antibiotic activity. The synthesis of these natural products requires appropriate regiospecific aromatic oxygenation of 2- acetylnaphthoquinone. Syntheses of 3-acetyl-5-methoxy-1, 4- naphthoquinone and the corresponding 5,7-dimethoxy analogue are described and the use of these in the syntheses of several naturally occurring pyranquinones or their derivatives, has been investigated. In the course of this work, an unusual Fries rearrangement and a novel baseinduced cyclisation were discovered - the latter affording several naphtho[2,3-c]pyrans in high yield. Previous routes to (±)-isoeleutherin and (±)-deoxyquinone A dimethyl ether have been recorded, but they give rise to a mixture of eleutherin and isoeleutherin in the first case, and a mixture of deoxyquinone A dimethyl ether and its cisdimethyl isomer. The synthetic routes to isoeleutherin and deoxyquinone A dimethyl ether developed during this investigation are highly stereoselective. The formation of the dimethyl ethers of quinones A and A', which is also highly stereoselective represents the first reported synthesis of the degradation products of the aphid pigments, protoaphin-fb and protoaphin-s1. The synthesis of 7-methoxyeleutherin is also described. The reaction of trifluoroacetic anhydride with various naphthalene derivatives is described and the potential of some of these acylated naphthalenes to be employed in the syntheses of naphtho[2, 3-c]pyrans and naturally occurring quinones has been investigated