Ma. Brimble et al., Double furofuran annulation to a bis-naphthoquinone: an approach to dimeric pyranonaphthoquinones, J CHEM S P1, (24), 1998, pp. 4165-4173
The preparation of bis-naphthoquinone 7, a key intermediate in the synthesi
s of dimeric pyranonaphthoquinones related to the actinorhodins is describe
d. Initial efforts directed to 7 which focussed on a double Fries rearrange
ment of bis-acetate 14 to 2-acetylnaphthol 13 were low yielding. Use of a S
tille coupling reaction between dimeric bromonaphthalene 20 and (alpha-etho
xyvinyl)tri-n-butyltin 19 as a means to introduce the acetyl groups at C-2
was also low yielding. The optimum route to bis-naphthoquinone 7 involved t
he synthesis of 2-acetylnaphthol 13 from bromide 25 using a Suzuki-Miyaura
coupling. Addition of 2-trimethylsilyloxyfuran to bis-naphthoquinone 7 affo
rded the bis-annulation adducts 30,31 which underwent double oxidative rear
rangement to bis-lactols 32,33. Reduction of the bis-lactols to bis-ethers
34,35 completed the first synthesis of a dimeric pyranonaphthoquinone.