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[摘要]：The bromination of dimethyl 8-methoxy-1,6,10-trimethylheptalene-4,5-dicarboxylate (6; Scheme 2) with N-bromosuccinimide (NBS) in N,N-dimethylformamide (DMF) leads in acceptable yields to the corresponding 9-bromoheptalenedicarboxylate 10 (Table 1). Ether cleavage of 6 with chlorotrimethylsilane (Me3SiCl)/NaI results in the formation of oxoheptalenedicarboxylate 13 in good yield (Scheme 4). The latter can be acetyloxylated to the (acetyloxy)oxoheptalenedicarboxylate 14 with Pb(OAc)(4) in benzene (Scheme 5). Oxo derivative 14, in turn, can be selectively O-methylated with dimethyl sulfate (DMS) in acetone to the (acetyloxy)methoxyheptalenedicarboxylates 15 and 15' (Scheme 6). The AcO group of the latter can be transformed into a benzyl or methyl ether group by treatment with MeONa in DMF, followed by the addition of benzyl bromide or methyl iodide (cf Scheme 9). Reduction of the ester groups of dimethyl 7,8-dimethoxy-5,6,10-trimethylheptalene-1,2-dicarboxylate (25') with diisobutylaluminium hydride (DIBAH) in tetrahydrofuran (THF) leads to the formation of the corresponding dimethanol 26', which can be cyclized oxidatively (IBX, dimethyl sulfoxide) to 8,9-dimethoxy-6,7,11-trimethylheptaleno[1,2-c]furan (27; Scheme 11). |
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