| Co-Investigator(Kenkyū-buntansha) |
KOYASU Yukio Mitsubishi Chemical Co., Chemical Laboratory, Research Scientist, 理化研究所, 副主任研究員
ISHII Youichi Univ. of Tokyo, Graduate School of Engineering, Lecturer, 大学院・工学系研究科, 講師 (40193263)
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| Budget Amount *help |
¥6,200,000 (Direct Cost: ¥6,200,000)
Fiscal Year 1996: ¥2,400,000 (Direct Cost: ¥2,400,000)
Fiscal Year 1995: ¥3,800,000 (Direct Cost: ¥3,800,000)
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| Research Abstract |
beta-Substituted pyrroles are widely found in biologically active compounds such as antibiotics, but this class of compounds can hardly be obtained by the conventional electrophilic substitution reactions of pyrrole. This research project aims at developing a novel synthetic method for beta-substituted pyrroles by utilizing molecular nitrogen as the nitrogen source.
Hydrazido (2-) complexes trans-[MX (NNH_2)(dppe)_2]^+ (M=Mo, W ; X=F,CL ; dppe=ph_2PCH_2CH_2PPh_2) and cis, mer-[WX_2 (NNH_2)(PMe_2Ph)_3](X=Cl, Br), which are readily derived from trans-[M (N_2)_2 (dppe)_2](1) and cis-[W (N_2)_2 (PMe_2Ph)_4]by protonation, condensed with 2,5-dimethoxytetrahydrofuran to afford pyrrolylimido complexes of the type trans-[MX (NNCH=CHCH=CH)(dppe)_2]^+ (2^+) and cis, mer-[WX_2 (NNCH=CHCH=CH)(PMe_2Ph)_3 (3), respectively. Their structures were characterized spectroscopically, and further confirmed by X-ray diffraction study. Electrophilic substitution reactions at the pyrrole ring in complexes 2^+
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occurred selectively at the beta-position to give the corresponding beta-substituted pyrrolylimido complexes trans-[MX (NNCH=C (E) CH=CH)(dppe)_2]^+ (E=Br, CN,SO_3^-, COR), although only chlorination of 2^+ with N-chlorosuccinimide in THF took place predominantly at the alpha-position, This beta-regioselectivity is in sharp contrast to the alpha-regioselectivity of free pyrrole, and is probably caused by the steric effect of the dppe ligands. Complexes 2^+ were readily reduced under ambient conditions with LiAlH_4 to liberate pyrrole and N-aminopyrrole in high yields. Further, the tetrahydrido complexes [MHH_4 (dppe)_4], which can be converted back into the original dinitrogen complexes 1, were recovered in moderate yields after the reduction. This accomplishes the synthetic cycle for pyrrole and N-aminopyrrole starting from the dinitrogen complexes 1. beta-Heptylpyrrole was also prepared starting from 2a^+ (M=W,X=Cl) by the beta-selective heptanoylation followed by the reduction with LiAlH_4. On the other hand, reduction of 3a (X=Br) with LiAlH_4 predominantly produced pyrrole, whereas treatment of 3a with KOH/EtOH liberated N-aminopyrrole in a high yield. Less
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