The synthesis of conjugated trienes and related oxidation products of α- farnesene (1), principally from the epoxides of α- farnesene (1), is reported. Base-promoted ring opening of 6,7-epoxide (4) by KOBut/LiNPri2 affords the conjugated triene (2), whilst the 3,4-epoxide (5) affords trienol (7). In contrast, 10,11-epoxide (6) fails to undergo epoxide ring opening; it rearranges to the conjugated triene epoxide (8). Base-promoted ring opening of bisepoxide (9) afforded trienol epoxide (11) at -30°C, whilst cyclization to tetrahydrofurans (10a,b) occurred at room temperature. Photosensitized oxidation of 10,11-epoxide (6) followed by in situ treatment with acid gave the cyclic peroxide (3) and on reduction triol (12). Bisallylic alcohol (13) was prepared by alkylation of 3-methylsulfolene with geranial. Trienes (2) and (3) have been isolated previously as autoxidation products of α- farnesene (1) and are implicated as the causal agents of superficial scald of stored apples.
The synthesis of 2-methylpyrrolo[l,2-alpyrazin-l(2H)-one (2) present in the insect feeding deterrent peramine (1) through oxidation of the saturated lactam (3) is described. The preparation of the related 6-methyl-1 H-pyrrolo[2,3-clpyridin-7(6 H)-one (12) through a Lewis-acid-catalysed cyclization of the amide acetal (7) is also described.
Addition of 2-trimethylsilyloxyfuran (19) to naphthoquinone (20) gave in 91% yield the furo [3,2-b] naphtho [2,1-d]furan (18) which upon treatment with ceric ammonium nitrate gave the hydroxy ester (24) in 70% yield. Attempts to induce an intramolecular transesterification of hydroxy ester (24) to bislactone (6), a key intermediate required for the synthesis of several pyranonaphthoquinone antibiotics, were unsuccessful. Hydroxy ester (24), however, is closely related to the antibiotic juglomycin (32).
The synthesis of aromatic spiroacetal ring systems related to the papulacandins is reported. ortho-Metalation of diisopropylbenzamide, followed by reaction with the electrophiles δ- valerolactone, γ- butyrolactone and γ-valerolactone, provided the keto alcohol adducts (10),(16) and (21) respectively. Reduction of the ketone followed by treatment with acid afforded phthalides (12),(18) and (23). Finally oxidative cyclization with iodobenzene diacetate provided the spiroacetals (7),(14) and (19).
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