Synergistic chiral iminium and palladium catalysis: Highly regio- and enantioselective [3 + 2] annulation reaction of 2-vinylcyclopropanes with enals

Abstract

SummaryA cooperative catalytic strategy of chiral iminium catalysis by regioselective activation of the C=C bond in enals and a transition metal promoting to open the 2-vinylcyclopropanes for highly regio- and enantioselective [3 + 2] cycloaddition reaction of 2-vinylcyclopropanes with α,β-unsaturated aldehydes has been developed.

Catalytic Enantioselective Ring-Opening Reactions of Cyclopropanes

“…Employing a closely related catalytic system, a similar transformation was reported by Wang and co-workers using diester-substituted VCPs . In these two first examples, addition of diphosphine ligands led to an improved yield and diastereoselectivity.…”

“…Employing a closely related catalytic system, a similar transformation was reported by Wang and co-workers using diester-substituted VCPs. 115 In these two first examples, addition of diphosphine ligands led to an improved yield and diastereoselectivity. In contrast, Rios and co-workers showed that employing diketo-substituted VCP 256 did not require any ligand on the palladium to deliver cyclopentanes such as 337−340 in good yields and enantioselectivities (Scheme 63A).…”

Synergistic formal ring contraction for the enantioselective synthesis of spiropyrazolones

“…Lately several groups have reported several synergistic cycloadditions for the formation of bicyclic and spiro products. Michelet, 5 Jørgensen, 6 Wei Wang 7 and Rios 8 reported a formal ring expansion of vinyl cyclopropanes with enals for the formation of spiro compounds under Pd(0) and secondary amine catalysis. Later on, Jørgensen reported vinyl aziridine opening 9 and [4 + 2] decarboxylation 10 ( Scheme 1 top) using a synergistic approach with excellent results.…”

Cooperative Palladium/Isothiourea Catalyzed Enantioselective Formal (3+2) Cycloaddition of Vinylcyclopropanes and α,β‐Unsaturated Esters

“…[20] A range of variants have since been developed, with nitroolefins, α,β-unsaturated keto esters and imines, activated indoles and benzofurans, and unsubstituted acrylic esters used as Michael acceptors, with the use of simple α,β-unsaturated esters currently representing a widely accepted limitation. [21] VCPs have also been employed in a dual catalytic setting as showcased by the independent reports from Vitale, [22] Jørgensen, [23] Wang [24] and Rios, [25] detailing the cooperative use of palladium and secondary amine catalysts to facilitate VCP ring opening and formal (3+2) cycloaddition with enals (Figure 1B), with the chiral organocatalyst (S)-1 responsible for enantioinduction. A range of related enantioselective processes have since been developed.…”