The roles of Lewis acidic additives in organotransition metal catalysis

Abstract

We present recent advances in prominent organotransition metal-catalysed reactions in which Lewis acid cocatalysts are employed to increase catalyst activity or selectivity. The roles of Lewis acids are discussed.

Catalytic One‐Pot Conversion of Renewable Platform Chemicals to Hydrocarbon and Ether Biofuels through Tandem Hf(OTf)4+Pd/C Catalysis

“…At this stage, TfOH was investigateda sacatalyst to determine whether the observed catalytic reactions were the result of metal triflate hydrolysis. [19] Althoughr esults comparable to those with 0.5 mol %H f(OTf) 4 wereo btained in HAA using 1-2mol %T fOH (Table S1, entries [11][12][13], significantly lower selectivity and carbon balance were observed in the one-pot reactions catalyzed by as eries of TfOH concentrations following either Modality Ao rB ,m imicking partial hydrolysis scenarios (Table S4). [8b] These results demonstrate the distinctive role of Hf(OTf) 4 beyond that of amere Brønsted acid precursor.…”

“…EtOAc also underwent HDO to AcOH in this case. When starting from enals, significant isomerization products are still observed, even with Modality B( Ta ble 2, entries [13][14][15][16][17][18][19]. For entries 15 and 17, target C n could not be distinguished from their isomers by GC.…”

Synthesis of [6,6,m]-Tricyclic Compounds via [4+2] Cycloaddition with Au or Cu Catalyst

“…19 When cyclization reaction was carried out with o-alkynylbenzaldehyde using a gold catalyst, [6,7,5]-tricyclic compound was obtained as major product through Huisgen-type [3+2] cycloaddition. And [6,6,6]-tricyclic compound was obtained by [4+2] cycloaddition reaction. 20 Our group is recently interested in the synthesis of abietane diterpenoid skeleton [6,6,6]-tricyclic compound.…”

“…We reported on the synthesis of 1-oxomiltirone and arucadiol, which belong to the class of abietane diterpenoids, from diyne using gold and copper catalysts. 21 In this paper, we have described the synthesis of various [6,6,6]-tricyclic compounds that can be used as building blocks for natural product abietane diterpenoid skeleton synthesis via transition-metal-catalyzed cyclization reaction. In addition, we have discussed the pathway to synthesize [6,6,7]-tricyclic compounds by increasing the carbon tether of the substrate.…”

“…Diynal substrate 1a was synthesized by palladiumcatalyzed Sonogashira coupling reaction of the diyne obtained from the alkylation of dimethyl malonate and 2-bromobenzaldehyde. 22 The [6,6,6]-tricyclic compound 1b was synthesized by an intramolecular [4+2] cycloaddition reaction using copper and gold catalysts. The product yield was high, when the process was carried out with a gold catalyst at 80 °C for 2 h or with a copper catalyst at 60 °C for 1 h (entry 1).…”