Two Approaches to the Aromatic Core of the Aminonaphthoquinone Antibiotics

Two
complementary approaches are presented for the synthesis of
the quinone chromophores of the naphthoquinone ansamycins and related
natural products. The first involves the use of an improved protocol
for the manganese­(III) acetate mediated cyclization of 5-aryl-1,3-dicarbonyl
compounds to β-naphthols, leading to the simple, scalable preparation
of building blocks suitable for the synthesis of naturally occurring
aminonaphthoquinones. The second approach involves the Diels–Alder
reaction of a series of new, ester-containing Danishefsky-type dienes
with N-protected aminobenzoquinones to allow more
expeditious access to similar intermediates.