Synthesis of 2,5-disubstituted pyrroles via dehydrogenative condensation of secondary alcohols and 1,2-amino alcohols by supported platinum catalysts

Abstract

Direct synthesis of 2,5-disubstituted pyrroles has been achieved via acceptorless dehydrogenative heterocyclization of 1,2-aminoalcohols and secondary alcohols by utilizing a heterogeneous carbon-supported Pt catalyst (Pt/C). The optimized method gave 92 % yield of 2-ethyl-5-phenyl-1H-pyrrole as a desired product from 2-amino-1-butanol and 1-phenylethanol in the presence of 0.1 mol% of Pt/C and 1.1 equiv. of KOtBu. It has been revealed that Pt/C demonstrates superior catalytic activity to a number of catalysts tested in this study including other transition metal-loaded carbon and various metaloxide-supported Pt catalysts. In addition, turnover number (TON) obtained in the present system was found to be higher than those obtained in previously-reported catalytic systems. It is significant that the Pt/C catalyst could be recycled as a heterogeneous catalyst without significant loss in the activity and showed wide substrate scope for the 2,5-disubstituted pyrrole forming process.

A Synthetic Methodology for Pyrroles from Nitrodienes

“…2‐Ethyl‐5‐(4‐methoxyphenyl)‐1 H ‐pyrrole (2e): White solid; yield: 72 %. 1 H NMR (300 MHz, CDCl 3 ): δ = 8.07 (br.…”

Efficient [Cu(NHC)]‐Catalyzed Multicomponent Synthesis of Pyrroles

“…Later on, a ruthenium pincer catalyst was reported by Milstein and co‐workers for this two‐component reaction that reached up to 88 % yield in refluxing toluene for 24 h in the presence of 0.5 equiv of KO t Bu . Saito and co‐workers described a similar approach for a Ru‐catalyzed synthesis of pyrroles from the corresponding β‐aminoalcohol and a ketone, whereas Shimizu and co‐workers used supported platinum catalysts in the presence of sec ‐alcohols instead of ketones. Beller and co‐workers have reported a three‐component reaction involving a primary amine or ammonia, a ketone, and a diol (Scheme c), using a Ru/Xantphos catalyst in the presence of 0.2 equiv of KO t Bu in t ‐amyl alcohol at 130 °C for 16 h, providing access to various substituted pyrroles in up to 92 % yield .…”

Recent Advancements in Pyrrole Synthesis

“…In this example, Shimizu reported the synthesis of 2,5-disubstituted pyrroles 235 from 1,2-amino alcohols 233 and secondary alcohols 234 in the presence of heterogeneous carbon-supported platinum as catalyst and a stoichiometric amount of KOt-Bu. 116 Mechanistically, the reaction commences with Pt-catalyzed dehydrogenation of the secondary alcohol to give ketone 236, which condenses with the 1,2-amino alcohol 234 to form imine 237. A second Pt-catalyzed dehydrogenation sequence allows the formation of imine aldehyde 238, which undergoes base-catalyzed dehydrative cyclization to furnish substituted pyrrole 235.…”