Journal of the Chemical Society. Perkin transactions I p. 1197 - 1202 (1981)
Update date:2022-08-16
Topics:
Kometani, Tadashi
Takeuchi, Yoshio
Yoshii, Eiichi
Two routes for the synthesis of (+/-)-nanaomycin A (1) starting with 2-bromo-8-methoxy-1,4-naphtoquinone (2) are described.The benzindanone (3) prepared from (2) in three steps was treated with methylmagnesium iodide and then with hydrochloric acid to afford the benzindene (8).Lemieux-Johnson oxidation of (8) gave the ketoaldehyde (9), which was converted into the conjugated ester (10) by reaction with methoxycarbonylmethylenetriphenylphosphorane.Reductive cyclisation of (10) with sodium borohydride afforded a ca. 1:1.9 mixture of the cis-naphthopyran (11) and its trans-isomer (12).Oxidative demethylation of (11) and (12) with cerium(IV) followed by treatment with aluminium chloride yielded the corresponding quinones (15) and (16).Ester hydrolysis of (16) formed (+/-)-nanaomycin A (1).Reductive methylation of the 2-allyl derivative of (2) afforded the bromonaphthalene (18), which was treated with butyl-lithium followed by acetaldehyde to give the naphthylcarbinol (19).The lactol (20) obtained by Lemieux-Johnson oxidation of (19) was treated with trimethyl phosphonoacetate-sodium hydride to yield a ca. 2.1:1 mixture of the naphthopyrans (11) and (12).Cyclisation of (19) with mercury(II) acetate-sodium borohydride yielded a ca. 1:0.9 mixture of the cis-naphthopyran (21) and its trans-isomer (22), which were oxidatively demethylated to give (+/-)-eleutherin (4) and (+/-)-isoeleutherin (5) respectively.
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