Enantioselective Ficini Reaction: Ruthenium/PNNP‐Catalyzed [2+2] Cycloaddition of Ynamides with Cyclic Enones

Abstract

Chiral cyclobuteneamides made easy: Double chloride abstraction from the ruthenium/PNNP complex 1 in the presence of unsaturated β‐keto esters 2 gives the dicationic adducts [Ru(2)(PNNP)]2+ (3) that catalyze the [2+2] cycloaddition of a variety of ynamides 4 to produce cyclobuteneamides 5 with high yield and enantioselectivity (see scheme).

Cyclobutane and Cyclobutene Synthesis: Catalytic Enantioselective [2+2] Cycloadditions

“…In 2011, Mezzetti, reported ac atalytic enantioselective [2+ +2] cycloaddition of the cyclopentenone derivative 87 with ynamides (i.e., Ficini Reaction), [33] and it was promoted by the dicationic ruthenium/PNNP complex 90 (Scheme 13). [34] The [3.2.0] products (89, 91,a nd 92)w ere generally formed in good enantioselectivity and yield. Reactions with cyclohexenone derivatives proceeded with much lower levels of enantioselectivity (78.5:21.5 e.r.…”

Effect of protic additives in Cu-catalysed asymmetric Diels–Alder cycloadditions of doubly activated dienophiles: towards the synthesis of magellanine-type Lycopodium alkaloids

“…1–3 In addition to being extremely reactive Michael acceptors in simple conjugate additions 3,4 and formal 2+2 cycloadditions, 5 their potential as dienophiles in Diels–Alder cycloadditions has been widely exploited, because of the ubiquity of the resulting hydrindane core in various classes of natural products when 5-membered cyclic analogs are used. 2 While many racemic and diastereoselective examples of Diels–Alder cycloadditions using alkylidene β-ketoesters as dienophiles have been reported, successful catalytic asymmetric variants remain scarce and typically lack generality with respect to the structure of the diene and dienophile.…”

A Chiral N,N′‐Dioxide–ZnII Complex Catalyzes the Enantioselective [2+2] Cycloaddition of Alkynones with Cyclic Enol Silyl Ethers

“…[3][4][5][6][7][8][9] However, regarding catalytic asymmetric version, only af ew examples have been reported during the past decades. [12,13] In 2014, Bach [14] and co-workers documented an enantioselective [2+ +2] photo-cycloaddition of 2-pyridones with acetylenedicarboxylates.For chiral Lewis acid promoted [2+ +2] cycloaddition, there are three types of reaction models according to the electronic nature of the substrates (see Scheme 1): Cycloaddition with electron-deficient alkenes and electron-rich alkynes (type I), [15,16] Ficini reaction (type II), [17] and formal cycloaddition between polarized electron-rich alkenes and electron-poor alkynes (type III). [12,13] In 2014, Bach [14] and co-workers documented an enantioselective [2+ +2] photo-cycloaddition of 2-pyridones with acetylenedicarboxylates.For chiral Lewis acid promoted [2+ +2] cycloaddition, there are three types of reaction models according to the electronic nature of the substrates (see Scheme 1): Cycloaddition with electron-deficient alkenes and electron-rich alkynes (type I), [15,16] Ficini reaction (type II), [17] and formal cycloaddition between polarized electron-rich alkenes and electron-poor alkynes (type III).…”

“…[10,11] Chiral transition-metal catalysts were found to be efficient for the [2+ +2] cycloaddition of alkynes with strained bicyclic alkenes. [12,13] In 2014, Bach [14] and co-workers documented an enantioselective [2+ +2] photo-cycloaddition of 2-pyridones with acetylenedicarboxylates.For chiral Lewis acid promoted [2+ +2] cycloaddition, there are three types of reaction models according to the electronic nature of the substrates (see Scheme 1): Cycloaddition with electron-deficient alkenes and electron-rich alkynes (type I), [15,16] Ficini reaction (type II), [17] and formal cycloaddition between polarized electron-rich alkenes and electron-poor alkynes (type III). [18] Fortype Iand type II cycloadditions (Scheme 1a,b), electron-rich alkynes are required, so Sand Natoms are commonly introduced.…”