Reactions of a Ruthenium Complex with Substituted N‐Propargyl Pyrroles. Issue 7 (25th February 2016)

• Record Type: Journal Article
• Authors: Chia, Pi‐Yeh; Huang, Shou‐Ling; Liu, Yi‐Hong; Lin, Ying‐Chih
• Is Part Of: Chemistry, an Asian journal. Volume 11:Issue 7(2016)
• Page Start: 1098
• Page End: 1106
• Publication Date: 2016-02-25
• Subjects: cyclization -- heterocycles -- ruthenium -- structure–activity relationships -- vinylidenes; Chemistry -- Periodicals; 540.5
• DOI: 10.1002/asia.201600074
• Languages: English
• ISSNs: 1861-4728

Abstract

Abstract: In an investigation into the chemical reactions of N ‐propargyl pyrroles1 a –c, containing aldehyde, keto, and ester groups on the pyrrole ring, with [Ru]−Cl ([Ru]=Cp(PPh3 )2 Ru; Cp=C5 H5 ), an aldehyde group in the pyrrole ring is found to play a crucial role in stimulating the cyclization reaction. The reaction of1 a, containing an aldehyde group, with [Ru]−Cl in the presence of NH4 PF6 yields the vinylidene complex2 a, which further reacts with allyl amine to give the carbene complex6 a with a pyrrolizine group. However, if1 a is first reacted with allyl amine to yield the iminenyne8 a, then the reaction of8 a with [Ru]−Cl in the presence of NH4 PF6 yields the ruthenium complex9 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 of2 a by R4 NOH yields the neutral acetylide complex3 a . In the presence of NH4 PF6, the attempted alkylation of3 a resulted in the formation the Fischer‐type amino–carbene complex5 a as a result of the presence of NH3, which served as a nucleophile. With KPF6, the alkylation of3 a with ethyl and benzyl bromoacetates afforded the disubstituted vinylidene complexes10 a and11 a, containing ester groups, which underwent deprotonation reactions to give the furyl complexes12 a and13 a, respectively. For13 a, containing an O‐benzyl group, subsequent 1, 3‐migration of the benzyl group was observed to yield product14 a with a lactone unit. Similar reactivity was not observed for the corresponding N ‐propargyl pyrroles1 b and1 c, which contained keto and ester groups, respectively, on the pyrrole ring. Abstract : Accept no substitutes : In the chemical reactions of N ‐propargyl pyrroles, containing aldehyde, keto, and ester groups on the pyrrole ring, with [Ru]−Cl ([Ru]=Cp(PPh3 )2 Ru; Cp=C5 H5 ), an aldehyde group in the pyrrole ring is found to play a crucial role in stimulating the cyclization reaction (see scheme).