Three component coupling, “cation

Three Component Coupling based on the Cation Pool Method... 

Thus, an Af-acyliminium ion pool 4 was allowed to react with an enamine derivative 8 (Scheme 8). The addition of the cation to the carbon-carbon double bond generated the second cation 9, which seemed to exist either as the open form or the cyclic form. In the next step, cation 9 was treated with allyltrimethylsilane to give the final three component coupling product 10. 

Previously, Ohashi and his co-workers reported the photosubstitution of 1,2,4,5-tetracyanobenzene (TCNB) with toluene via the excitation of the charge-transfer complex between TCNB and toluene [409], The formation of substitution product is explained by the proton transfer from the radical cation of toluene to the radical anion of TCNB followed by the radical coupling and the dehydrocyanation. This type of photosubstitution has been well investigated and a variety of examples are reported. Arnold reported the photoreaction of p-dicyanobenzene (p-DCB) with 2,3-dimethyl-2-butene in the presence of phenanthrene in acetonitrile to give l-(4-cyanophenyl)-2,3-dimethyl-2-butene and 3-(4-cyanophenyl)-2,3-dimethyl-l-butene [410,411], The addition of methanol into this reaction system affords a methanol-incorporated product. This photoreaction was named the photo-NO-CAS reaction (photochemical nucleophile-olefin combination, aromatic substitution) by Arnold. However, a large number of nucleophile-incorporated photoreactions have been reported as three-component addition reactions via photoinduced electron transfer [19,40,113,114,201,410-425], Some examples are shown in Scheme 120. 

Other nucleophiles that have been used in this context are acetylides (alkynes). The addition of those to iminium cations generated in situ from aldehydes and secondary amines accomplishes a gold(III)-catalyzed three-component coupling for the synthesis of propargylamines, as can be observed in equation (124). The reactions are performed in water or in tetrahydrofuran (THF) when supported catalysts are employed.Chiral prolinol derivatives as... 

This review article deals with addition and cycloaddition reactions of organic compounds via photoinduced electron transfer. Various reactive species such as exdplex, triplex, radical ion pair and free radical ions are generated via photoinduced electron transfer reactions. These reactive species have their characteristic reactivities and discrimination among these species provides selective photoreactions. The solvent and salt effects and also the effects of electron transfer sensitizers on photoinduced electron transfer reactions can be applied to the selective generation of the reactive species. Examples and mechanistic features of photoaddition and photocycloaddition reactions that proceed via the following steps are given reactions of radical cations with nucleophiles reactions of radical anions with electrophiles reactions of radical cations and radical anions with neutral radicals radical-radical coupling reactions addition and cycloaddition reactions via triplexes three-component addition reactions. 

The key element of this protocol is the initial addition of cationic electrophiles such as rerr-alkyl or acyl cations to the double bond of a DCHC complex of the conjugated enyne 118, which results in the formation of the substituted propargylic cation intermediate 119, Subsequent reaction with pre-selected external nucleophiles, for example allylsilanes or silyl enol ethers, leads to the formation of the final adducts 120. The reaction is carried out as a one-pot, three-component coupling and can be used for the creation of two novel C-C bonds. It is a process somewhat complementary to the stepwise Michael addition described earlier (Scheme 2.31), with a reverse order of E and Nu addition. Oxidative decomplexation of 120 yields the product 121. The overall... 

Sc(OTf)3 and Yb(( ) l r), are quite valuable catalysts of the aza-DA reaction of 102 [204] (Scheme 10.113). Wifh these catalysts, three-component coupling of aldehydes, anilines, and 102 proceeds smoothly [304]. Sc(OSO2C8Fi7)3 enables an efficient aza-DA reaction in supercritical CO2 [305]. Cationic lanthanide complexes, [(C5Me5)2Ce][BPh4] and fhe corresponding Sm and La complexes, have high catalytic activity in the HDA reaction of 102 with aromatic aldehydes [306]. 

The reaction of an N-acyliminium ion pool with an alkene or alkyne followed by trapping of the resulting carbocation by water leads to the formation of the corresponding carbohydroxylation product. Cationic sequential one-pot, three-component coupling reactions of an N-acyliminium ion can also be accomplished using an electron-rich olefin and a suitable nucleophile that traps the thus-generated cationic intermediate as shown in Scheme 5.17. ... 

Suga S, Nishida T, Yamada D et al (2004) Three-component coupling based on the cation pool method. J Am Chem Soc 126 14338-14339... 

Suga S, Yamada D, Yoshida J (2010) Cationic three-component coupling involving an optically active enamine derivative. Prom time integration to space integration of reactions. Chem Lett 39 404 05... 

When the radical cation DX does not undergo fragmentation, as is typical when arising from an olefin, an alternative is found in the attack by a nucleophile Nu". The resulting radical X-D-Nu couples with the aryl radical anion ArZ " and regains aromaticity, yielding again a three-components adduct X-ArD-Nu [the NOCAS (Nucleophile Olefin Combination Aromatic Substitution) process, as shown in Scheme 14.2, path g [14, 15]. In Scheme 14.2, the aromatic compound... 

The reactions initiated by the addition of a carbon-carbon multiple bond to the cation pool bring in unique one-pot transformations otherwise difficult to realize, because the reactive carbocations are existing in the solution in relatively high concentration. For example, a sequential one-pot three-component coupling reactions have been developed (Scheme 5) [9, 10]. [4 -f 2] cyclo addition reactions in which an N-acyliminium ion was used as a hetero diene [11], and cationic carbohydroxylation of alkenes and alkynes using the cation pool method [12] were also accomplished. 

Cation-Pool Method, Scheme 5 One-pot three component coupling... 

Ryu and coworkers reported a highly enantioselective and (Z)-stereocontrolled three-component coupling reaction of a,P-acetylenic esters, aldehydes, and tri-methylsilyl iodide (TMSI) using chiral cationic oxazaborolidinium catalysts (Scheme 31.42) [54]. Both enantiomers of (Z)-P-iodo MBH esters (R/S) could be obtained enantioselectively by using an (S)- or (R)-oxazaboroUdinium salts (143 or 144), which behave as chiral Lewis acids and have been proven to be effective catalysts for Diels-Alder reactions, cyanosilylations, and Michael reactions. These esters can be directly converted into the optically active (Z)-P-branched derivatives... 

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