Cooperative Pd(0)/Rh(II) Dual Catalysis: Interceptive Capturing of π-Allyl Pd(II) Complexes with α-Imino Rh(II) Carbenoids

Abstract

Extensive effort has been expended to utilize π-allyl palladium-complexes as electrophilic allyl donor intermediates in cooperative dual catalysis, but their counter anions such as carboxylates or alkoxides are almost always discarded as waste. We have developed a cooperative Pd(0)/Rh(II) dual catalysis system that utilizes both the electrophilic allyl and nucleophilic counter anion functionalities inherent in the starting allylic substrates. In this cooperative catalysis, redox compatible Pd(0) and Rh(II) catalysts selectively activate allylic substrates and N-sulfonyl-1,2,3-triazoles to generate π-allyl Pd(II)-complexes and 1,3-ambivalent equivalent aimino Rh(II)-carbenoid intermediates, respectively. The counter anion of the π-allyl Pd(II)-complex acts as a nucleophile transferring to the electrophilic carbenic carbon to form Pd/Rh-associated zwitterionic intermediates, in which the cationic palladium species may coordinate with both counter anion and imine nitrogen in the same plane establishing the (Z)-geometry of the products.

π-Allylpalladium Complexes in Synthesis: An Update

“…The chemo-and stereoselectivity of the coupling is proposed to be due to the coordination of the imine nitrogen with the Lewis acidic -allyl-Pd(II) (Scheme 17). 25…”

Chemo‐selective Rh(II)/Pd(0) Dual Catalysis: Synthesis of All‐Carbon C3‐Quaternary Allylic Oxindoles from N‐Aryl‐α‐Diazo‐β‐Keto‐Amides with Functionalized Allyl Carbonates

“…In their work, Ru(II)‐associated enolate intermediate C , which was obtained by Ru(II)‐catalyzed C−H functionalization of 4‐(trifluoromethyl)‐phenyl‐substituted α ‐diazoamide, has undergone Pd(0)‐catalyzed asymmetric allylic alkylation with simple allyl tert ‐butyl carbonate to afford chiral 3‐allyl‐3‐aryl oxindoles in good ee (Scheme b) . We also presented a series of Rh(II)/Pd(0) dual‐catalyzed allylic substitution involving Rh(II)‐carbenoids and π ‐allyl Pd(II) intermediates –. In recent, we developed a synergistic Rh(II)/Pd(0) dual‐catalysis that promotes the de‐alkylated allylation of Rh(II)‐associated alkylic oxonium ylides D from α ‐diazo‐ β ‐keto‐esters with functionalized π‐ allyl Pd(II) intermediates E , accomplishing the synthesis of highly functionalized dihydrofuran‐3‐one derivatives with an O ‐substituted quaternary carbon center(above, Scheme c) .…”

“…A number of studies have succeeded in controlling the chemo‐selectivity of transition‐metal carbenoid –. In initial studies, we selected N ‐aryl‐ α ‐diazo‐ β ‐ketoamide 1 a and allyl tert ‐butyl carbonate 2 a as model substrates by using a redox‐compatible Rh(II)/Pd(0) dual catalytic system –. Thus, when the reaction was carried out at 50 °C in the presence of 1.0 mol% Rh 2 ( t BuCO 2 ) 4 , 2.0 mol% Pd 2 (dba) 3 , and 4.8 mol% Xantphos.…”

Dual Rh(II)/Pd(0) Relay Catalysis for One‐Pot Synthesis of α‐Quaternary Allylated Indolin‐2‐ones and Benzofuran‐2‐ones

“…Despite considerable recent advances, 2 the dual catalytic systems composed of two‐different transition‐metals are still limited, which may attributed in part to the inherent difficulty in insuring of redox compatibility between the catalysts and balanced kinetics, avoiding catalyst deactivation 3 . In this regards, we have previously demonstrated for the first time the redox‐compatibility between Rh(II) and Pd(0) catalysts through the synergistic cooperative Rh(II)/Pd(0) dual catalytic reaction between N ‐sulfonyl‐1,2,3‐triazoles and allylic substrates 4a . More recently, we have reported a tandem dual Rh(II)/Pd(0) relay catalysis to afford α‐quaternary allylated β‐lactams through the Rh(II)‐catalyzed C(sp 3 )‐H insertion, followed by Pd(0)‐catalyzed allylic alkylation (Scheme 1(b)).…”

“…More recently, we have reported a tandem dual Rh(II)/Pd(0) relay catalysis to afford α‐quaternary allylated β‐lactams through the Rh(II)‐catalyzed C(sp 3 )‐H insertion, followed by Pd(0)‐catalyzed allylic alkylation (Scheme 1(b)). 4b In present work, we extended the tandem dual Rh(II)/Pd(0) relay catalytic reaction for one‐pot synthesis of C3‐quaternary allylated five‐membered heterocyclic compounds through the sequential aromatic C(sp 2 )‐H functionalization/allylation of α‐diazoamides and α‐diazoesters (Scheme 1(c)). 5 …”