- Uncatalyzed addition of N-(tert-butoxycarbonyl)-2-tert-butyldimethylsilyloxypyrrole to activated quinones
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The uncatalyzed addition of N-(tert-butoxycarbonyl)-2-tert-butyldimethylsilyloxypyrrole 3 to 1,4-quinones bearing an electron withdrawing group at C-2 is reported. Use of 2-methoxycarbonyl-1,4-benzoquinone 4 and 2-methoxycarbonyl-1,4-naphthoquinone 5 provided an efficient synthesis of the pyrrolidinobenzofuran adduct 9 and the corresponding pyrrolidinonaphthofuran adduct 10, respectively, whereas use of 2-acetyl-1,4-benzoquinone 6, 2-acetyl-1,4-naphthoquinone 7 and 2-acetyl-8-methoxy-1,4-naphthoquinone 8 formed silyloxypyrroles 11, 12, and 13 resulting from direct electrophilic substitution of the silyloxypyrrole by the electrophilic quinone. Addition of PPTs to the reaction of 2-acetyl-8-methoxy-1,4-naphthoquinone 8 with N-(tert-butoxycarbonyl)-2-tert-butyldimethylsilyloxypyrrole 3 afforded pyrrolidinonaphthofuran adduct 14 which then underwent smooth oxidative rearrangement to pyrrolidino pyranonaphthoquinone 15, thereby providing a novel approach for the synthesis of aza-analogues of the pyranonaphthoquinone antibiotics such as kalafungin 16.
- Brimble, Margaret A.,Halim, Rosliana,Petersson, Maria
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- Synthesis of 5-epi-7-Deoxykalafungin and 5-epi-7-O-Methylkalafungin
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The syntheses of 5-epi-7-deoxykalafungin (12a) and 5-epi-7-o-methylkalafungin (12b), compounds closely related to the pyranonaphthoquinone antibiotic kalafungin (1), have been completed making use of the transformation of the one tricyclic ring system into another.The uncatalysed 1,4-addition of 2-trimethylsilyloxyfuran (4) to the 2-acetyl-1,4-naphthoquinones (8) gave the furonaphthofurans (9) which underwent facile oxidative rearrangement, in 72-76percent yield using cerium(IV) ammonium nitrate, to the furonaphthopyrans (11) which contain the same ring system as the natural product kalafungin (1).Reduction of the hemiacetals (11) to the cyclic ethers (12) was effected using triethylsilane in trifluoracetic acid.The analogous rearrangement of the furobenzofuran (5a) to the furobenzopyran (6) proceeded in only 27percent yield.Further insight into the mechanism of the intial 1,4-addition reaction was gained by isolation of the intermediate (13) in the reaction of 2-trimethylsilyloxyfuran (4) with the naphthoquinone (8a).
- Brimble, Margaret A.,Stuart, Susan J.
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p. 881 - 885
(2007/10/02)
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- REARRANGEMENT OF A FURONAPHTHOFURAN TO A PYRANONAPHTHOQUINONE
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The ceric ammonium nitrate oxidation of the furonaphthofuran-8(9H)-ones (5c,5d) gave the rearranged hemiketals (11c,11d) in 72-76percent yield.Reduction of the hemiketals (11c,11d) provided an entry to a pyranonaphthoquinone with a fused γ-lactone as present in the pyranonaphthoquinone antibiotics kalafungin (6) and nanaomycin D (7).
- Brimble, Margaret A.,Hodges, Richard,Stuart, Susan J.
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p. 5987 - 5990
(2007/10/02)
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