Reactions of a Ruthenium Complex with Substituted N‐Propargyl Pyrroles |
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| Authors: | Pi‐Yeh Chia Shou‐Ling Huang Yi‐Hong Liu Prof?Dr Ying‐Chih Lin |
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| Affiliation: | 1. Department of Chemistry, National Taiwan University, Taipei, Taiwan;2. (+886)?223636359
0000-0002-5887-0880
Department of Chemistry, National Taiwan University, Taipei, Taiwan |
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| Abstract: | In an investigation into the chemical reactions of N‐propargyl pyrroles 1 a – c , containing aldehyde, keto, and ester groups on the pyrrole ring, with Ru]?Cl (Ru]=Cp(PPh3)2Ru; Cp=C5H5), an aldehyde group in the pyrrole ring is found to play a crucial role in stimulating the cyclization reaction. The reaction of 1 a , containing an aldehyde group, with Ru]?Cl in the presence of NH4PF6 yields the vinylidene complex 2 a , which further reacts with allyl amine to give the carbene complex 6 a with a pyrrolizine group. However, if 1 a is first reacted with allyl amine to yield the iminenyne 8 a , then the reaction of 8 a with Ru]?Cl in the presence of NH4PF6 yields the ruthenium complex 9 a , containing a cationic pyrrolopyrazinium group, which has been fully characterized by XRD analysis. These results can be adequately explained by coordination of the triple bond of the propargyl group to the ruthenium metal center first, followed by two processes, that is, formation of a vinylidene intermediate or direct nucleophilic attack. Additionally, the deprotonation of 2 a by R4NOH yields the neutral acetylide complex 3 a . In the presence of NH4PF6, the attempted alkylation of 3 a resulted in the formation the Fischer‐type amino–carbene complex 5 a as a result of the presence of NH3, which served as a nucleophile. With KPF6, the alkylation of 3 a with ethyl and benzyl bromoacetates afforded the disubstituted vinylidene complexes 10 a and 11 a , containing ester groups, which underwent deprotonation reactions to give the furyl complexes 12 a and 13 a , respectively. For 13 a , containing an O‐benzyl group, subsequent 1,3‐migration of the benzyl group was observed to yield product 14 a with a lactone unit. Similar reactivity was not observed for the corresponding N‐propargyl pyrroles 1 b and 1 c , which contained keto and ester groups, respectively, on the pyrrole ring. |
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| Keywords: | cyclization heterocycles ruthenium structure– activity relationships vinylidenes |
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