Phthalazine 2-oxide (I) reacted with dimethyl acetylenedicarboxylate (IIa) to afford 2-phthalazinium 3-methoxy-1-methoxycarbonyl-2, 3-dioxopropylide (III), methyl pyrrolo [2, 1-α] phthalazine-1, 2, 3-tricarboxylate (IVa), methyl 2-hydroxy-1, 3-naphthalenedicarboxylate (V), methyl 1, 2-epoxy-2, 3-naphthalenedicarboxylate (VIa) and VII (C
17H
15NO
7). Compound I reacted with methyl propiolate (IIb) to afford methyl pyrrolo [2, 1-α]-phthalazine-1, 3-dicarboxylate (IVb), methyl 3-hydroxy and 4-hydroxy-2-naphthalenecarboxylate (IXa, IXb), and methyl 3, 4-epoxy-2-naphthalenecarboxylate (VIb). The structures of XIII, XIV and XVII, which were obtained in the reaction of 1-phenylphthalazine 3-oxide (XII) with II, were presumed to be methyl 1-phenyl-2-methoxycarbonyl-α-oxo-indene-2-ethanoate (XIII), methyl 1-phenyl-2-benzoxepine-3, 4-dicarboxylate (XIV), and methyl 3-hydroxy-4-phenyl-2-naphthalenecarboxylate (XVII), respectively. It is considered that these products are formed by the liberation of nitrogen from 1, 3-dipolar cycloadducts.
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