Synthesis of a pyranonaphthoquinone-spiroacetal

Abstract

A synthesis of pyranonaphthoquinone-spiroacetal 12 is reported which represents an efficient entry to the pentacyclic framework of the pyranonaphthoquinone antibiotic griseusin A. The key step involves assembly of the furo[3,2-b]naphtho[2,3-d]pyran 11via a ceric ammonium nitrate oxidative rearrangement of the furo[3,2-b]naptho[2,1-d]furan 10. This latter heterocycle 10 in turn was constructed via the uncatalysed 1,4-addition of 2-trimethylsilyloxyfuran 9 to naphthoquinone 8. Naphthoquinone 8 is readily available from 1,4-dimethoxynaphthalene-2-carbaldehyde 3 and acetylene 4.